NOVEL AVIAN CYTOKINES AND GENETIC SEQUENCES ENCODING SAME

Abstract: The present invention relates generally to recombinant polypeptides having avian cytokine properties or avian cytokine-like properties and to genetic sequences encoding same. More particularly, the present invention is directed to recombinant avian Type II interferon polypeptides and specifically to avian interferon- gamma (IFN- gamma ) and derivatives, homologues and analogues thereof and uses of same as an immune response modulator and as a growth enhancing agent.

Description: NOVEL AVIAN CYTOKINES AND GENETIC SEQUENCES ENCODING SAME The present invention relates generally to recombinant polypeptides having avian cytokine properties or avian cytokine-like properties and to genetic sequences encoding same. More particularly, the present invention is directed to recombinant avian Type II interferon polypeptides and specifically to avian interferon-γ (IFN-γ) and derivatives, homologues and analogues thereof and uses of same as an immune response modulator and as a growth enhancing agent. Bibliographic details of the publications referred to in this specification by author are collected at the end of the description. Sequence Identity Numbers (SEQ ID NOs.) for the nucleotide and amino acid sequences referred to in the specification are defined following the bibliography. Throughout this specification and the claims that follow, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising" will be understood to imply the inclusion of a stated element or integer or group of elements or integers, but not the exclusion of any other element or integer or group of elements or integers. The rapidly increasing sophistication of recombinant DNA technology is greatly facilitating research into the medical and veterinary fields. Cytokine research is of particular importance, especially as these molecules regulate the proliferation, differentiation and function of a great variety of cells, such as cells involved in mediating an immune response. Administration of recombinant cytokines or regulating cytokine function and/or synthesis is becoming, increasingly, the focus of medical research into the treatment of a range of disease conditions in humans and animals. In mammals, interferons (IFN) represent a family of cytokines that share the capacity to inhibit viral replication and to exert effects on immune function. There are two distinct types of IFN. Type I IFN is produced by a variety of cell types in response to viral infection and includes IFN-α and -β. Typically, IFN-α is produced by leukocytes such as monocytes and macrophages while fibroblasts and epithelial cells are the major source of IFN-β. Type I IFNs share a high degree of amino acid homology, bind to the same cell surface receptor and there biological functions are resistant to heat and low pH treatment. (Weissmann and Weber, 1986) In contrast, the production of Type II IFN-γ in mammals is restricted to activated T cells and NK cells and is encoded by a gene that is unrelated to those which express IFN-α or IFN-β. Features that distinguish IFN-γ from -α/β include their binding to different cell surface receptors and that the former is exquisitely sensitive to heat and low pH treatment (Weissmann and Weber, 1986). Another distinction is the ability of IFN-γ, but not IFN-α or IFN-β, to stimulate macrophages to produce reactive nitrogen intermediates such as nitric oxide, nitrate and nitrite (Fast et al, 1993; Huang et al, 1993). Chicken T cells produce IFN following stimulation with antigen or mitogen ( Prowse and Pallister, 1989; Lowenthal et al, 1993; Pusztai et al, 1986; Weiler and von Bulow, 1987; Dijkmans et al, 1990) as measured by the ability to protect chick embryonic fibroblasts (CEF) from virus-mediated lysis. There has been controversy as to whether this IFN activity is the Type I or Type II equivalent of mammalian IFN (Lillehoj et al, 1992). In fact, the existence of IFN-γ in avian species has been questioned (Dijkmans et al, 1990). The gene for chicken Type I IFN (ChlFN-α) has recently been cloned (Sekellick et al, 1994) and when the protein was compared to mammalian IFNs it was shown to have 20- 24% amino acid sequence identity to Type I IFNs, whereas it was unrelated to known inammalian IFN-γ polypeptides. Furthermore, recombinant ChlFN-α was shown to have antiviral activity, but lacked macrophage activating function in that it was unable to induce nitrite secretion in monocytes (Schultz et al, 1995), consistent with the properties of mammalian Type I IFN. In work leading up to the present invention, the inventors have generated several unique chicken T cell lines from reticuloendotheliosis virus (REV)-transformed spleen cell cultures (Lowenthal et al, 1995a,b). These T cell lines were cloned from single cells that expressed the T cell markers CD3 and CD4/CD8. The inventors have shown that some of these T cell clones constitutively produce high levels of an interferon having the properties of IFN-γ as determined by the ability of their supematants to prevent virus-mediated lysis of chicken embryonic fibroblasts (CEF), lability of the IFN activity to heat and low pH and the ability of these supematants to induce nitrite production by chicken macrophages. The inventors have generated a cDNA library from one of the cloned T cell lines producing an interferon-γ activity and successfully isolated and sequenced a nucleic acid molecule which encodes, or is complementary to a nucleic acid molecule which encodes avian IFN-γ (hereinafter referred to as "ChlFN-γ"). Recombinant genetic constructs comprising the isolated nucleic acid molecule of the present invention have been produced and expressed in transformed cells and immunoreactive molecules, in particular polyclonal and monoclonal antibodies have been produced to the recombinant IFN-γ polypeptide produced therefrom. Surpisingly, the IFN-γ of the present invention posseses many useful features, including the ability to promote growth of an avian species or to prevent weight loss during pathogenic infections when administered thereto by any means, in addition to the ability to act as an immunomodulatory molecule across species boundaries. Accordingly, one aspect of the present invention provides an isolated nucleic acid molecule which encodes, or is complementary to a nucleic acid molecule which encodes, an avian cytokine polypeptide or a functional or immunologically-interactive homologue, analogue or derivative thereof, wherein said polypeptide is a Type II interferon or a Type II interferon-like molecule. The term "avian" means a member of the class of vertebrates commonly referred to as birds. As used herein, the term "avian" includes both sexes and all developmental stages of poultry species, domestic birds and game birds selected from the list comprising chickens, turkeys, bantams, quails, guinea fowl, ducks, geese, ostriches, emus, pigeons, canaries, budgerigars, parrots and finches, amongst others. Hereinafter the term "cytokine polypeptide" shall be taken to refer to a polypeptide molecule comprising at least one subunit of a biologically-active protein which possesses one or more of the characteristic biological features of a cytokine, in particular the ability to affect the functions of a cell which functions in the immune system of an animal. Hereinafter the term "Type II interferon polypeptide" or "Type II interferon-like polypeptide" shall be taken to refer to a cytokine polypeptide as hereinbefore defined wherein said cytokine possesses at least one, preferably at least two, more preferably at least three, even more preferably at least four, still even more preferably at least five and most preferably six of the following characteristic properties: (i) It is capable of preventing virus-mediated lysis of an avian cell such as, but not limited to a chicken embryonic fibroblast cell or a turkey embryonic fibroblast cell; (ii)It is sensitive to treatment comprising high temperature, preferably temperatures of at least 50°C, more preferably at least 60°C; (iii)It is sensitive to exposure to low pH, preferably pH values between 1 and 6, more preferably pH values between 1 and 3, in particular a pH value of 2.0; (iv)It is capable of inducing macrophages to secrete reactive nitrogen intermediates such as nitrite, nitrate or nitric oxide, amongst others; (v) It functions as an immunomodulatory molecule in an avian species; and (vi)It functions as a growth-enhancing or growth-promoting agent in an avian species. A Type II interferon-like molecule will further possess characteristics not normally associated with an avian Type II interferon molecule as defined herein, however possesses sufficient similarity to a Type II interferon molecule to be immunologically cross-reactive thereto, or to be at least 40% similar thereto at the amino acid sequence level. References herein to "Type II interferon polypeptide" or "Type II interferon-like polypeptide" shall also be taken to include all possible fusion molecules between a said polypeptide as hereinbefore defined and another polypeptide, in particular a Type I interferon molecule such as IFN-α or IFN-β or, alternatively, a second Type II interferon or Type III interferon-like molecule. In a preferred embodiment however, references contained herein to "Type II interferon polypeptide" or "Type II interferon- like polypeptide" indicate an avian IFN-γ polypeptide or a fusion molecule comprising same or a derivative, homologue or analogue thereof. As used herein, the term "immunomodulatory molecule" shall be taken to refer to a polypeptide, protein or other substance which is at least capable of altering the immune response of an animal to a disease-promoting agent such as an infectious agent or a cancer-inducing agent, amongst others. Accordingly, the present invention is particularly directed to avian Type II interferon polypeptides which are at least capable of altering an immune response in a bird or alternatively a fusion molecule comprising same which is at least capable of altering an immune response in a bird or mammal to an antigen or infectious agent such as, but not limited to infectious bronchitis virus, avian infectious laryngeotracheitis virus, infectious bronchitis virus, Newcastle disease virus, Marek's Disease virus, chicken anemia virus, avian influenza virus, E.coli, Salmonella ssp., Eimeria ssp. or Mycoplasma ssp. amongst others, to alleviate symptoms associated therewith, in particular reduced growth performance. As used herein, the term "growth-enhancing or growth promoting agent" or similar term shall be taken to refer to the capability of a substance to lead to increased weight in an avian species or to prevent weight losses normally detectable during or following pathogenic infection of an avian species, when administered thereto, either in any form such as a vaccine, adjuvant, recombinant polypeptide, synthetic polypeptide, pharmaceutical composition or therapeutic foc*dstuff, amongst others. In a preferred embodiment, the present invention provides an isolated nucleic acid molecule which encodes, or is complementary to a nucleic acid molecule which encodes, an avian cytokine polypeptide a functional or immunologically-interactive homologue, analogue or derivative thereof, wherein said polypeptide is a Type II interferon or a Type II interferon-like molecule and wherein said avian is a species of poultry selected from the list comprising chickens, ducks, geese, turkeys, bantams, quails or guinea fowl, amongst others. In a particularly preferred embodiment, the nucleic acid molecule of the present invention is derived from chickens. As used herein, the term "derived from" shall be taken to indicate that a particular integer or group of integers has originated from the species specified, but has not necessarily been obtained directly from the specified source. In a more particularly preferred embodiment, the present invention provides an isolated nucleic acid molecule which encodes, or is complementary to a nucleic acid molecule which encodes, a chicken IFN-γ or IFN-γ-like polypeptide or a functional or immunologically-interactive homologue, analogue or derivative thereof. The nucleic acid molecule of the present invention most preferably comprises a sequence of nucleotides substantially the same as or complementary to the nucleotide sequence set forth in SEQ ID NO:l or a homologue, analogue or derivative thereof including any single or multiple nucleotide substitutions, deletions and or additions thereto. For the present purpose, "homologues" of a nucleotide sequence shall be taken to refer to an isolated nucleic acid molecule which is substantially the same as the nucleic acid molecule of the present invention or its complementary nucleotide sequence, notwithstanding the occurrence within said sequence, of one or more nucleotide substitutions, insertions, deletions, or rearrangements. "Analogues" of a nucleotide sequence set forth herein shall be taken to refer to an isolated nucleic acid molecule which is substantially the same as a nucleic acid molecule of the present invention or its complementary nucleotide sequence, notwithstanding the occurrence of any non-nucleotide constituents not normally present in said isolated SUBSTΓΓUTE SHEET (Rule 26) nucleic acid molecule, for example carbohydrates, radiochemicals including radionucleotides, reporter molecules such as, but not limited to DIG, alkaline phosphatase or horseradish peroxidase, amongst others. "Derivatives" of a nucleotide sequence set forth herein shall be taken to refer to any isolated nucleic acid molecule which contains significant sequence similarity to said sequence or a part thereof. Generally, the nucleotide sequence of the present invention may be subjected to mutagenesis to produce single or multiple nucleotide substitutions, deletions and/or insertions. Nucleotide insertional derivatives of the nucleotide sequence of the present invention include 5' and 3' terminal fusions as well as intra-sequence insertions of single or multiple nucleotides or nucleotide analogues. Insertional nucleotide sequence variants are those in which one or more nucleotides or nucleotide analogues are introduced into a predetermined site in the nucleotide sequence of said sequence, although random insertion is also possible with suitable screening of the resulting product being performed. Deletional variants are characterised by the removal of one or more nucleotides from the nucleotide sequence. Substitutional nucleotide variants are those in which at least one nucleotide in the sequence has been removed and a different nucleotide or nucleotide analogue inserted in its place. For the purposes of nomenclature, the nucleotide sequence set forth in SEQ ID NO: 1 relates to the chicken IFN-γ cDNA sequence, referred to hereinafter as the "ChlFN-γ gene" , which is expressed in activated T cells and NK cells to produce a polypeptide which is capable of stimulating macrophages to produce reactive nitrogen intermediates such as nitric oxide, nitrate or nitrite. Reference herein to a "gene", including the "ChlFN-γ gene", is to be taken in its broadest context and includes: (i) a classical genomic gene consisting of transcriptional and/or translational regulatory sequences and/or a coding region and/or non-translated sequences (i.e. introns, 5'- and 3'- untranslated sequences); and/or (ii) mRNA or cDNA corresponding to the coding regions (i.e. exons) optionally comprising 5'- or 3 '-untranslated sequences of the gene. The term "gene" is also used to describe synthetic or fusion molecules encoding all or part of a functional product. Synthetic ChlFN-γ genes may be derived from a naturally- occurring ChlFN-γ gene by standard recombinant techniques. Generally, an a ChlFN-γ gene may be subjected to mutagenesis to produce single or multiple nucleotide substitutions, deletions and/or additions. Nucleotide insertional derivatives of the ChlFN-γ cytokine gene of the present invention include 5' and 3' terminal fusions as well as intra-sequence insertions of single or multiple nucleotides. Insertional nucleotide sequence variants are those in which one or more nucleotides are introduced into a predetermined site in the nucleotide sequence although random insertion is also possible with suitable screening of the resulting product. Deletional variants are characterised by the removal of one or more nucleotides from the sequence. Substitution.--, nucleotide variants are those in which at least one nucleotide in the sequence has been removed and a different nucleotide inserted in its place. Such a substitution may be "silent" in that the substitution does not change the amino acid defined by the codon. Alternatively, substituents are designed to alter one amino acid for another similar acting amino acid, or amino acid of like charge, polarity, or hydrophobicity. The present invention extends to the isolated nucleic acid molecule when integrated into the genome of a cell as an addition to the endogenous cellular complement of cytokine genes. Optionally, the integrated nucleic acid molecule contains a promoter sequence derived from the same or another gene, which regulates the expression of the IFN-γ gene sequence contained therein. The subject invention clearly contemplates a related Type II interferon gene or interferon-like gene derived from an avian source in addition to chickens, such as but not limited to, any poultry species, domestic bird or game bird selected from the list comprising turkeys, bantams, quails, guinea fowl, ducks, geese, ostriches, emus, pigeons, canaries, budgerigars, parrots and finches, amongst others. The present invention extends further to said avian Type II interferon genes or Type II interferon-like genes derived from embryo tissues or cultured cells of avian origin. Preferably, the related avian Type II interferon gene, or Type II interferon-like gene, has utility in therapeutic foodstuffs or vaccine compositions as an immunomodulatory molecule or growth-enhancing agent for the treatment of animals such as, but not limited to birds, mamm--ls, or humans. Those skilled in the relevant art will easily be able to isolate one or more related Type II interferon or Type II interferon-like gene sequences without undue experimentation, when provided with the nucleotide sequence set forth in SEQ ID NO:l. As a consequence, the present invention extends to any avian Type II interferon genes or interferon-like genes and any functional genes, mutants, derivatives, parts, fragments, homologues or analogues thereof or non-functional molecules but which are at least useful as, for example, genetic probes, or primer sequences in the enzymatic or chemical synthesis of said gene, or in the generation of immunologically interactive recombinant molecules, subject to the proviso that said avian Type II interferon gene or interferon- like gene is at least 40% related to the nucleotide sequence set forth in SEQ ID NO:l. The present invention clearly encompasses a genomic clone equivalent of the nucleic acid molecule set forth in SEQ ID NO.l wherein said genomic clone comprises at least a part of the ChlFN-γ gene. Accordingly, an alternative embodiment of the present invention provides an isolated nucleic acid molecule which comprises a sequence of nucleotides corresponding or complementary to the sequence of nucleotides set forth in SEQ ID NO:l, or having at least about 40%, preferably at least about 55%, still more preferably at least about 65%, yet still more preferably at least about 75-80% and even still more preferably at least about 85-95% nucleotide similarity to all or a part thereof. In a particularly preferred embodiment, the present invention provides an isolated nucleic acid molecule which encodes or is complementary to a nucleic acid molecule which encodes an avian cytokine polypeptide or a functional or immunologically-interactive homologue, analogue or derivative thereof, wherein said polypeptide is a Type II interferon or a Type II interferon-like molecule and wherein said nucleic acid molecule further comprises a sequence of nucleotides which is at least 40% identical to the nucleotide sequence set forth in SEQ ID NO:l In a most preferred embodiment of the invention, said Type II interferon molecule is IFN-γ, in particular ChlFN-γ. In an alternative embodiment, the present invention provides an isolated nucleic acid molecule which encodes, or is complementary to a nucleic acid molecule which encodes, an avian Type II interferon or avian Type-II interferon-like polypeptide and which is capable of hybridising under at least low stringency conditions to the nucleic acid molecule set forth in SEQ ID NO: 1, or to a complementary strand thereof. Preferably, said nucleic acid molecule is capable of hybridising under at least moderate stringency conditions, even more preferably under at least high level stringency conditions. In a most preferred embodiment of the invention, said Type II interferon is IFN-γ, in particular ChlFN-γ. For the purposes of defining the level of stringency, a low stringency is defmed herein as being a hybridisation and/or a wash carried out in όxSSC buffer, 0.1% (w/v) SDS at 28°C. A moderate stringency is defined herein as being a hybridisation and/or wash carried out in 2xSSC buffer, 0.1% (w/v) SDS at a temperature in the range 45°C to 65°C. A high stringency is defined herein as being a hybridisation and/or wash carried out in O.lxSSC buffer, 0.1% (w/v) SDS at a temperature of at least 65°C. Generally, the stringency is increased by reducing the concentration of SSC buffer, and/or increasing the concentration of SDS and/or increasing the temperature of the hybridisation and/or wash. Those skilled in the art will be aware that the conditions for hybridisation and/or wash may vary depending upon the nature of the hybridisation membrane or the type of hybridisation probe used. Conditions for hybridisations and washes are well understood by one normally skilled in the art. For the purposes of SUBS Γ clarification of the parameters affecting hybridisation between nucleic acid molecules, reference is found in pages 2.10.8 to 2.10.16. of Ausubel et al. (1987), which is herein incorporated by reference. In a further alternative embodiment, the present invention provides an isolated nucleic acid molecule which encodes or is complementary to a nucleic acid molecule which encodes an avian cytokine polypeptide or a functional or immunologically-interactive homologue, analogue or derivative thereof, wherein: (i) said polypeptide is a Type II interferon or a Type II interferon-like molecule; (ii) said nucleic acid molecule comprises a sequence of nucleotides which is at least 40% identical to the nucleotide sequence set forth in SEQ ID NO: 1 ; and (iii) said nucleic acid molecule is capable of hybridising under at least low stringency conditions to the nucleic acid molecule set forth in SEQ ID NO: 1, or to a complementary strand thereof. Preferably, said Type II interferon molecule is IFN-γ, in particular ChlFNγ. A second aspect of the present invention provides a method for identifying an avian Type II interferon genetic sequence, or avian Type II interferon-like genetic sequence or a homologue, analogue or derivative thereof. In one embodiment, said method comprises contacting genomic DNA, or mRNA, or cDNA with a hybridisation effective amount of a Type II interferon genetic sequence, or a functional part thereof, and then detecting said hybridisation. The related genetic sequence may be in a recombinant form, in a virus particle, bacteriophage particle, yeast cell, animal cell, or a plant cell. Preferably, the related genetic sequence originates from an avian species. More preferably, the related genetic sequence originates from an avian species selected from the list comprising chickens, turkeys, bantams, quails, guinea fowl, ducks, geese, ostriches, emus, pigeons, canaries, budgerigars, parrots and finches, amongst others. In a particularly preferred embodiment the related genetic sequences originate from chickens. Preferably, the avian Type II interferon genetic sequence (i.e probe or latter genetic sequence) comprises a sequence of nucleotides or at least 50 nucleotides, more preferably at least 100 nucleotides and even more preferably at least 500 nucleotides derived from the nucleotide sequence set forth in SEQ ID NO: 1 or its complement or a homologue, analogue or derivative thereof. Preferably, the latter genetic sequence is labelled with a reporter molecule capable of giving an identifiable signal (e.g. a radioisotope such as P or S or a biotinylated molecule). An alternative embodiment of the present invention provides a method for identifying an avian Type II interferon genetic sequence, or avian Type II interferon-like genetic sequence or a homologue, analogue or derivative thereof comprising contacting two non- complementary nucleic acid "primer molecules" of at least 12 nucleotides in length derived from the nucleotide sequence of an avian Type II cytokine gene with a nucleic acid template molecule comprising nucleotide sequences related to the primer molecule sequences and amplifying specific nucleic acid molecule copies of the template molecule in a polymerase chain reaction. According to this embodiment, the first primer molecule is preferably derived from the sense strand of an avian IFN-γ gene such as the ChlFN-γ gene and in particular from the nucleotide sequence set forth in SEQ ID NO:l or a homologue, derivative or analogue thereof and the second primer molecule is preferably derived from the antisense strand of an avian IFN-γ gene such as the ChlFN-γ gene and in particular from the complement of the nucleotide sequence set forth in SEQ ID NO:l or a homologue, derivative or analogue thereof. Accordingly, both primers hybridise to said template molecule such that, in the presence of a DNA polymerase enzyme, a cofactor and appropriate substrate, DNA synthesis occurs in the 5' to 3' direction from each primer molecule towards the position on the DNA where the other primer molecule is hybridised, thereby amplifying the intervening DNA. The nucleic acid primer molecule may further consist of a combination of any of the nucleotides adenine, cytidine, guanine, thymidine, or inosine, or functional analogues or derivatives thereof, capable of being incorporated into a polynucleotide molecule provided that it is capable of hybridising under at least low stringency conditions to the nucleic acid molecule set forth in SEQ ID NO:l. The nucleic acid primer molecules may further be each contained in an aqueous pool comprising other nucleic acid primer molecules. More preferably, the nucleic acid primer molecule is in a substantially pure form. The nucleic acid template molecule may be in a recombinant form, in a virus particle, bacteriophage particle, yeast cell, animal cell, or a plant cell. Preferably, the related genetic sequence originates from an avian cell, tissue, or organ. More preferably, the related genetic sequence originates from a chicken cell, tissue or organ. A third aspect of the present invention provides a genetic construct comprising a nucleic acid molecule which encodes or is complementary to a nucleic acid molecule which encodes an avian cytokine polypeptide or a homologue, analogue or derivative thereof, wherein said polypeptide is a Type II interferon or a Type II interferon-like molecule. In a preferred embodiment, said polypeptide is IFN-γ. In a particularly preferred embodiment, the present invention provides a genetic construct comprising the nucleotide sequence set forth in SEQ ID NO: 1 or a homologue, analogue or derivative thereof. The genetic constructs of the present invention are particularly useful for the production of the recombinant cytokine polypeptide encoded therein, when introduced into a cell line or a virus particle and under conditions suitable for gene expression to occur. Such conditions will depend upon the cell line and the expression vector used in each case and would be well-known to the person skilled in the art. Any number of expression vectors can be employed depending on whether expression is required in a eukaryotic or prokaryotic cell or a virus particle. Furthermore, it is well-known in the art that the promoter sequence used in the expression vector will also vary depending upon the level of expression required and whether expression is intended to be constitutive or regulated. For expression in eukaryotic cells, the genetic construct generally comprises, in addition to the nucleic acid molecule of the invention, a promoter and optionally other regulatory sequences designed to facilitate expression of said nucleic acid molecule. The promoter may be derived from a genomic clone encoding an avian Type II interferon molecule, in particular ChlFN-γ or, aletematively, it may be a heterologous promoter from another source. Promoter sequences suitable for expression of genes in eukaryotic cells are well- known in the art. In a preferred embodiment, the promoter is capable of expression in an avian cell. Examples of eukaryotic cells contemplated herein to be suitable for expression include avian, mammalian, yeast, insect, plant cells or cell lines such as COS, NERO, HeLa, mouse C127, Chinese hamster ovary (CHO), WI-38, baby hamster kidney (BHK) or MDCK cell lines. Such cell lines are readily available to those skilled in the art. In connection with this invention, a nucleic molecule comprising the nucleotide sequence set forth in SEQ ID ΝO:l has been cloned into the plasmid vector pCDNA3, which is suitable for expression in eukaryotic COS cells, to produce the plasmid pCDNA3/avian G-IFN. Isolated COS cells containing the pCDNA3/avian G-IFN genetic construct have been deposited on 28 February, 1995 pursuant to and in satisfaction of the Budapest Treaty on the International Recognition of the Deposit of Microorganisms for the Purposes of Patent Procedure, with the Australian Government Analytical Laboratories (AGAL), 1 Suakin Street, Pymble, New South Wales 2073, Australia, under AGAL Accession No. N95/12388. The prerequisite for producing intact polypeptides in E.coli is the use of a strong promoter with an effective ribosome binding site. Typical promoters suitable for expression in bacterial cells such as E. coli include, but are not limited to, the lacz promoter, temperature-sensitive λ L or λ R promoters, T7 promoter or the IPTG-inducible tac promoter. A number of other vector systems for expressing the nucleic acid molecule of the invention in E.coli are well-known in the art and are described for example in Ausubel et al (1987) or Sambrook et al (1989). Numerous plasmids with suitable promoter sequences for expression in bacteria and efficient ribosome binding sites have been described, such as for example, pKC30 (λ L :Shimatake and Rosenberg, 1981), pKK173-3 {tac: Amann and Brosius, 1985), pET- 3 (T7: Studier and Moffat, 1986) or the pQE series of expression vectors (Qiagen, CA), amongst others. Suitable prokaryot'c cells include corynebacterium, salmonella, Escherichia coli, Bacillus sp. and Pseudomonas sp, amongst others. Bacterial strains which are suitable for the present purpose are well-known in the relevant art (Ausubel et al, 1987; Sambrook et α/,1989). In connection with this invention, a nucleic molecule comprising the nucleotide sequence set forth in SEQ ID NO:l has been cloned into a plasmid vector suitable for expression in a bacterial cell and transformed into the bacterium Escherichia coli to produce E.coli strain pQE ChlFN-γ. The E.coli strain pQE ChlFN-γ has been deposited on 16 February, 1996 pursuant to and in satisfaction of the Budapest Treaty on the International Recognition of the Deposit of Microorganisms for the Purposes of Patent Procedure, with the Australian Government Analytical Laboratories (AGAL), 1 Suakin Street, Pymble, New South Wales 2073, Australia, under AGAL Accession No. N96/9464. In an alternative embodiment, the present invention extends to a genetic construct comprising a nucleic acid molecule which encodes or is complementary to a nucleic acid molecule which encodes an avian cytokine polypeptide or a homologue, analogue or derivative thereof, wherein said polypeptide is a fusion polypeptide between a Type II interferon or Type II interferon-like molecule and either a second Type II interferon or interferon-like molecule or a Type I interferon selected from the list comprising IFN-α, IFN-β, Ch IFN-α or Ch IFN-β, amongst others. Preferably, said Type II interferon is IFN-γ, in particular Ch IFN-γ. In order to produce a fusion polypeptide, the nucleic acid molecule which encodes a first coding region comprising an avian cytokine polypeptide or a homologue, analogue or derivative thereof is cloned adjacent to a second coding region, optionally separated by a spacer nucleic acid molecule such that the first coding region and the second coding region are in the same open reading frame, with no intervening stop codons between the two coding regions. When translated, the polypeptide thus produced comprises a fusion between the polypeptide products of the first and second coding regions. A genetic construct which encodes a fusion polypeptide further comprises at least one start codon and one stop codon, capable of being recognised by the cell's translational machinery in which expression is intended. Methods for the production of a fusion polypeptide are well-known to those skilled in the art. A still further aspect of the present invention provides a recombinant avian cytokine polypeptide or a functional or immunologically-interactive homologue, analogue or derivative thereof, wherein said polypeptide is a Type II interferon or a Type II interferon-like molecule. By "recombinant avian cytokine" or related term "recombinant molecule" is meant a glycosylated or unglycosylated polypeptide molecule, including a fusion polypeptide, with or without other associated molecules (eg. lipids) produced by recombinant means such as presence of a DNA molecule in an expression vector in the correct reading frame relative to a promoter and introducing the resultant recombinant expression vector into a suitable host and growing said host under conditions appropriate for expression and, if necessary, transportation of uie recombinant protein or its derivative from said host and then purifying the recombinant molecule. In a particularly preferred embodiment of the present invention, there is provided a recombinant polypeptide comprising a sequence of amino acids which is substantially SUBSTITUTE SHEET Rnle 26 the same as the amino acid sequence set forth in SEQ ID NO:2 or is at least 40% identical to same. The present invention extends to any derivatives of the avian cytokine polypeptide set forth in SEQ ID NO:2. For the purposes of nomenclature, the amino acid sequence set forth in SEQ ID NO:2 is chicken IFN-γ (ChlFN-γ) polypeptide which is expressed in activated T cells and NK cells to produce a polypeptide which is capable of stimulating macrophages to produce reactive nitrogen intermediates such as nitric oxide, nitrate or nitrite. Derivatives of an avian Type II interferon polypeptide or interferon-like polypeptide include single or multiple amino acid substitutions, deletions and/or additions to the molecule. Conveniently, these are prepared by first making single or multiple nucleotide substitutions, deletions and/or additions to the nucleic acid molecule encoding the avian cytokine. Alternatively, once the amino acid sequence is known, amino acids can be chemically added by established techniques and in any sequence required to give the desired mutant. All such derivatives are encompassed by the present invention. Amino acid insertional derivatives of the avian Type II interferon or interon-like polypeptide of the present invention include amino and/or carboxyl terminal fusions as well as intra-sequence insertions of single or multiple amino acids. Insertional amino acid sequence variants are those in which one or more amino acid residues are introduced into a predetermined site in the protein although random insertion is also possible with suitable screening of the resulting product. Deletional variants are characterised by the removal of one or more amino acids from the sequence. Substitutional amino acid variants are those in which at least one residue in the sequence has been removed and a different residue inserted in its place. Typical substitutions are those made in accordance with Table 1. Where a derivative avian cytokine is produced by amino acid substitution, the amino acids are generally replaced by other amino acids having like properties, such as hydrophobicity, hydiυpholicity, electronegativity, bulky side chains and the like. Amino acid substitutions are typically of single residues. Amino acid insertions will usually be in the order of about 1-10 amino acid residues and deletions will range from about 1-20 residues. Preferably, deletions or insertions are made in adjacent pairs, i.e. a deletion of two residues and a corresponding insertion of two residues. For convenience and by way of shorthand notation, reference herein to an avian cytokine, in particular an avian Type II interferon such as IFN-γ, Ch IFN-γ or an avian interferon-like polypeptide includes reference to any derivatives thereof as contemplated above. TABLE 1 Suitable residues for amino acid substitutions Original Residue Exemplary Substitutions Ala Ser Arg Lys Asn Gin; His Asp Glu Cys Ser Gin Asn; Glu Glu Asp Gly Pro His Asn; Gin He Leu; Val Leu He; Val Lys Arg; Gin; Glu Met Leu; He; Val Phe Met; Leu; Tyr Ser Thr Thr Ser Trp Tyr Tyr Tφ; Phe Val He; Leu; Met The amino acid variants referred to above may be readily made using synthetic peptide techniques well known in the art, such as solid phase peptide synthesis and the like, or by recombinant DNA manipulations. Techniques for making substitution mutations at predetermined sites in DNA having known or partially known sequence are well known and include, for example, M13 mutagenesis. The manipulation of DNA sequence to produce variant proteins which manifest as substitutional, insertional or deletional variants are conveniently described, for example, in Ausubel et al (1987) or Sambrook et al (1989). Other examples of recombinant or synthetic mutants and derivatives of the avian Type II interferon polypeptide of the present invention include single or multiple substitutions, deletions and/or additions of any molecule associated with the enzyme such as carbohydrates, lipids and/or proteins or polypeptides. A further aspect of the invention provides a method of producing a recombinant avian Type II interferon or Type II interferon-like molecule in a cell comprising expressing in said cell a nucleic acid molecule which encodes or is complementary to a nucleic acid molecule which encodes said avian cytokine. In a related embodiment, the present invention provides a method of producing a recombinant avian Type II interferon or interferon-like molecule in a cell comprising the steps of: (i) introducing into said cell a genetic construct comprising a nucleic acid molecule which encodes or is complementary to a nucleic acid molecule which encodes said avian cytokine, placed under the control of a suitable promoter sequence; (ii) culturing said cell for a time and under conditions sufficient for said nucleic acid molecule to be expressed; and (iii) optionally isolating from said cell said recombinant cytokine molecule. In a further related embodiment, the present invention extends to a method of producing a recombinant avian cytokine molecule in a cell comprising introducing into said cell a genetic construct comprising a nucleic acid molecule which encodes or is complementary to a nucleic acid molecule which encodes an avian cytokine polypeptide or a homologue, analogue or derivative thereof, wherein said polypeptide is a fusion polypeptide between a first Type II interferon or Type II interferon-like molecule and a second Type II interferon or a Type I interferon selecteu from the list comprising IFN- α, IFN-β, Ch IFN-α or Ch IFN-β, amongst others. Preferably, said method further comprises the step of introducing said genetic construct into said cell prior to the step of obtaining expression thereof. According to the foregoing embodiments described in this aspect of the invention, the recombinant cytokine or Type II interferon or interferon-like molecule is preferably an IFN-γ polypeptide molecule or a f sion molecule comprising same. In a particularly preferred embodiment, the cytokine is the ChlFN-γ polypeptide set forth in SEQ ID NO:2 or a homologue, analogue or derivative thereof or a fusion molecule comprising same. For optimum expression in a particular tissue or under specified conditions, the nucleic acid molecule may be placed operably under the control of a promoter sequence such as those discussed supra. Suitable cells and virus particles for this purpose are also discussed supra. Promoter sequences and culture conditions for cells or virus particles which produce high levels of expression will be well-known to those skilled in the relevant art. A further aspect of the invention provides an isolated cell which expresses an endogenous or recombinant avian cytokine polypeptide or a functional or irnmunologically-interactive homologue, analogue or derivative thereof, wherein said polypeptide is a Type II interferon or a Type II interferon-like molecule. In a preferred embodiment, the present invention provides an isolated cell which expresses an avian cytokine, wherein said cytokine is a Type II interferon or a Type II interferon-like molecule. More preferably, said cytokine is a recombinant molecule, for example a fusion polypeptide between a Type II interferon molecule and a second cytokine molecule. In a most preferred embodiment, the Type II interferon molecule according to this aspect of the invention is IFN-γ, in particular Ch IFN-γ or a homologue, analogue or derivative thereof. The isolated cell may be an isolated eukaryotic cell which expresses a non-recombinant form of said cytokine, Type II interferon or Type II interferon-like molecule. In connection with this invention, an isolated T-cell clone designated as CCδ.lh which expresses the ChlFN-γ gene has been deposited on 10 October, 1994 pursuant to and in satisfaction of the Budapest Treaty on the International Recognition of the Deposit of Microorganisms for the Purposes of Patent Procedure, with the Australian Government Analytical Laboratories (AGAL), 1 Suakin Street, Pymble, New South Wales 2073, Australia, under the Accession No. N94/46035. Alternatively, the isolated cell may be a transformed eukaryotic or prokaryotic cell which expresses a recombinant cytokine, Type II interferon or Type II interferon-like molecule from a genetic construct, such as those discussed supra, which has been introduced thereto. Means for introducing genetic constructs into a cell will be well- known to those skilled in the art. Accordingly, by way of example, there is provided in a most particularly preferred embodiment, an isolated bacterial cell expressing recombinant ChlFN-γ, wherein said cell has been deposited with the Australian Government Analytical Laboratory on 16 February, 1996 under AGAL Accession No. N96/9464. Also by way of example, the present invention provides an isolated eukaryotic cell expressing recombinant ChlFN-γ, wherein said cell has been deposited with the Australian Government Analytical Laboratory on 28 February, 1995 under AGAL Accession No. N95/12388. In a further embodiment, the present invention extends to an isolated cell comprising a genetic construct as hereinbefore defined. Means for isolating a cell which expresses an endogenous or recombinant avian cytokine such as a Type II interferon or interferon-like molecule will be well-known to those skilled in the art. The cells of the present invention are useful as a source of purified avian cytokines, in particular Type II interferon molecules or interferon-like molecules. The recombinant avian Type II interferon or interferon-like molecules contemplated herein or cells expressing same, will find particular application in the intensive livestock industries such as the live animal export trade, feed-lots and intensive rearing industries. In particular, livestock such as poultry, domestic birds and game birds are highly susceptible to infectious diseases, such as those transmitted by viruses, bacteria or mycoplasma. Important viral infectious agents include infectious bursal disease virus, avian infectious bronchitis virus, avian infectious laryngeotracheitis virus, infectious bronchitis virus, Newcastle disease virus, Marek's Disease virus, chicken anemia virus or avian influenza virus, amongst others. Important bacterial agents include E.coli, Salmonella ssp. or Eimeria ssp., amongst others. Whilst not being bound by any theory or mode of action, avian cytokines such as Type II interferons or interferon-like molecules, in particular ChlFN-γ induce macrophages to become activated, as measured by the increased expression of Class II molecules on their surfaces and/or the increased secretion of active nitrogen intermediates such as nitrites, thereby increasing the capacity of the immune system to destroy invading pathogens and to enhance the immune response thereto. Accordingly, in a further aspect of the present invention there is provided a method of treatment or prophylaxis of poultry, domestic birds or game birds exposed to or infected with a pathogenic organism, said method comprising administering to said animal an immunomodulatingly effective amount of an avian cytokine or a derivative thereof for a time and under conditions sufficient to maintain, stimulate or enhance the immmunoresponsiveness of said animal. Preferably, said avian cytokine is a recombinant molecule. As used herein, the term "immunomodulatingly effective amount" is an amount of cytokine sufficient to effect immunomodulation in a target animal, i.e. to enhance the ability of the immune system to develop an effective immune response or to enhance the immunocompetence of the animal or immunogenicity of an antigen administered thereto. According to the foregoing embodiment, it is particularly preferred that said avian cytokine is a Type II interferon molecule or Type II interferon-like molecule, in particular IFN-γ. In a most particularly preferred embodiment, said avian cytokine is ChlFN-γ, such as the ChlFN-γ polypeptide molecule set forth in SEQ ID NO:2 or a homologue, analogue or derivative thereof. The term "poultry, domestic bird or game bird" as used herein extends to chickens, turkeys, bantams, quails, guinea fowl, ducks, geese, ostriches, emus, pigeons, canaries, budgerigars, parrots and finches, amongst others, provided that the avian cytokines are effective in those animals. Particularly preferred poultry, domestic bird or game birds are chickens and related species. The present invention is of particular use in the treatment or prophylaxis of poultry, domestic birds or game birds against infection by pathogens selected from the list comprising infectious bursal disease virus, avian infectious bronchitis virus, avian infectious laryngeotracheitis virus, infectious bronchitis virus, Newcastle disease virus, Marek's Disease virus, chicken anemia virus, avian influenza virus, E.coli, Salmonella ssp., Eimeria ssp. or Mycoplasma ssp. amongst others. The avian cytokine of the present invention may be administered throughout the life cycle of a bird for which treatment or prophylaxis is indicated. The developmental stage of the bird during which treatment or prophylaxis is most effective will vary depending upon the nature of the pathogen against which protection is sought, including its mode cf transmission and period of highest infectivity. By "period of highest infectivity" is meant the developmental stage of the host during which it is most vulnerable to attack by a particular pathogen and or during which there is a greater probaoility of incurring livestock losses or reduced productivity as a result of the pathogen infection. The parameters affecting optimum developmental stages of animals for administration of the subject cytokines will be well-known to those skilled in the art. Accordingly, the method of treatment or prophylaxis of the present invention extends to administration of the subject avian cytokine at any developmental stage in the life cycle of poultry, domestic or game birds for which treatment or prophylaxis is indicated. The cytokine of the invention may be administered by any means including for example, by injection either in ovo or post-hatching by injection such as intra-peritoneal, intra- dermal, intra-muscular, intra-ocular, intra- venous, sub-cutaneous or other injection means, by ingestion as a medicated foodstuff or therapeutic foodstuff or by introducing to said avian an isolated nucleic acid molecule which encodes or is complementary to a nucleic acid molecule which encodes said cytokine or, alternatively, a vector comprising a genetic construct capable of expressing said cytokine in vivo or in ovo, for example a live recombinant viral vector, live recombinant bacterial vector. Wherein the cytokine of the invention is aclministered via the introduction of an isolated nucleic acid molecule encoding said cytokine, such as a DNA or RNA molecule, or a vector comprising a genetic construct capable of expressing said cytokine, the nucleic acid molecule or genetic construct must be transcribed and translated to produce the biologically-active cytokine molecule following its administration to an appropriate avian subject. In an alternative embodiment, the present invention provides a method of treatment or prophylaxis of poultry, domestic birds or game birds exposed to or infected with a pathogenic organism, said method comprising administering to said animal an immunoresponsive effective amount of a first avian cytokine comprising a Type II interferon or Type II interferon-like molecule in combination with a second avian cytokine molecule, for a time in combination and under conditions sufficient to maintain, stimulate or enhance the immunoresponsiveness of said animal. Preferably, said first avian cytokine is an IFN-γ molecule in particular Ch IFN-γ. It is also preferred that said second avian cytokine be selected from the list comprising Type I interferons such as, but not limited to, IFN-α, IFN-β, ChlFN-α, ChlFN-β, or a Type II interferon or any other cytokine or cytokine-like molecule. In a most preferred embodiment, said first avian cytokine and said second avian cytokine are a fusion molecule. According to this embodiment of the invention, the first and second avian cytokines interact with the immune system of an animal to further stimulate or enhance the immunoresponsiveness of the immune system against pathogen attack. Another important application of the cytokines of the present invention is as natural adjuvants for vaccines, particularly for subunit or synthetic peptide vaccines produced by recombinant DNA technology. The term "adjuvant" as used herein shall be taken to mean a substance that, when administered to an animal in combination with a second substance or antigen, enhances the production of immunointeractive molecules, such as antibodies, which recognise the second substance or antigen molecule. An adjuvant may be used therapeutically to produce antibodies against small amounts of antigen or to prolong the period of antibody production or to increase the amount of antibody produced. Whilst not wishing to be bound by any theory or mode of action, adjuvants work by inducing a local influx of antibody-forming cells to the site of administration. Accordingly, a further aspect of the present invention provides an adjuvant comprising an avian cytokine molecule, wherein said cytokine is a Type II interferon or interferon- like molecule or a fusion molecule between said Type II interferon molecule and a second cytokine molecule and optionally, apharmaceutically-acceptable carrier, excipient or diluent. Preferably, said avian Type II interferon molecule is IFN-γ, in particular ChlFN-γ. In a most particularly preferred embodiment, said ChiFN-γ molecule comprises an amino acid sequence which is substantially the same as the amino acid sequence set forth in SEQ ID NO:2 or at least 40% identical thereto. Wherein said avian cytokine is a fusion molecule, said second cytokine may be any cytokine molecule which is functional in avian species, in particular IFN-α, IFN-β, ChlFN-α, ChlFN-γ or a Type II inferon molecule or any other cytokine or cytokine-like molecule. In accordance with the present invention, an avian cytokine such as a Type II interferon or interferon-like molecule, in particular ChlFN-γ, is used in vaccines to enhance the immunogenicity of antigens, particularly in subunit vaccines, leading to increased antibody titre in individual birds, increased protection of birds that are immunised against a specific antigen (i.e. enhanced flock immunity) and/or increased persistence of protective antibodies in immunised birds. A further advantage provided by the present invention is a reduction in the quantity of specific antigen required to effectively immunise animals, thereby leading to reduced production costs. A still further aspect of the present invention provides a method of enhancing and or stimulating an immune response to one or more antigens in an animal, said method comprising administering to said animal an immunoresponsive effective amount of an avian cytokine. In a related embodiment, there is contemplated a vaccine composition for the prophylactic treatment of an avian species comprising an antigen and recombinant avian cytokine or a derivative thereof as described herein. The vaccine may also comprise one or more pharmaceutically acceptable carriers and or diluents. The carriers and/or diluents are also required to be acceptable for veterinary use. According to this embodiment of the invention, said prophylactic treatment is intended to vaccinate said avian against a viral or bacterial pathogen selected from the list comprising infectious bursal disease virus, avian infectious bronchitis virus, avian infectious laryngeotracheitis virus, infectious bronchitis virus, Newcastle disease virus, Marek's Disease virus, chicken anemia virus, avian influenza virus, E.coli, Salmonella ssp. or Eimeria ssp. , amongst others. According to the foregoing embodiments, it is particularly preferred that said avian cytokine is a Type II interferon molecule or interferon-like molecule, in particular IFN-γ or a fusion polypeptide between avian Type II interferon molecule and a second cytokine. In a most particularly preferred embodiment, said avian cytokine is ChlFN-γ, such as the ChlFN-γ polypeptide molecule set forth in SEQ ID NO:2 or a homologue, analogue or derivative thereof. The cytokine or vaccine of the invention described according to these embodiments may be administered by any means including for example, by injection either in ovo or post- hatching by injection such as intra-peritoneal, intra-dermal, intra-muscular, intra-ocular, intra- venous, sub-cutaneous or other injection means, by ingestion as a medicated foodstuff or therapeutic foodstuff. Advances in slow-release technology and the development of live non-pathogenic bacteria and viruses as delivery vectors for these molecules will ensure their cost- effectiveness when aclministered to poultry, domestic birds or game birds. They may also be used in nucleic acid vaccination. Accordingly, the avian cytokine or vaccine of the present invention may also be delivered by genetic means. For example, recombinant avian ChlFN-γ may be encoded by a genetic construct present in a delivery system such as a virus, yeast, bacterium, protozoan, insect, avian or mammalian cell. The expression of such a delivery system in a target animal will enable delivery of the recombinant avian cytokine. According to this embodiment, there is contemplated a genetic construct comprising: (i) a first nucleotide sequence encoding an avian Type II interferon or interferon-like molecule or a fusion cytokine molecule between said Type II interferon and a second cytokine, placed operably under the control of a first promoter sequence; (ii) a second nucleotide sequence defining an antigen against which immunisation is required, placed operably under the control of a second promoter sequence;and (iii) a delivery vehicle comprising genetic sequences which facilitate replication of said genetic construct in a delivery cell such as a bacterial, yeast, insect, a protozoan animal or a mammalian cell. Preferably, said Type II interferon is IFN-γ, in particular ChlFN-γ. It is also preferred that said second cytokine be selected from the list comprising Type I interferons such as IFN-α, IFN-β, ChlFN-α, ChlFN-β or, alternatively, a Type II interferon or interferon-like molecule or any other cytokine or cytokine-like molecule. According to this embodiment, the delivery cell would not in normal use be harmful or pathogenic to the target animal. Conveniently, attenuated delivery cells are employed. Particularly useful delivery vectors are attenuated viruses and recombinant viral and bacterial vectors. For example, an attenuated viral vector is used as a live vaccine. The genetic sequence encoding an avian cytokine such as ChlFN-γ or a derivative thereof is cloned into the viral sequence and the recombinant virus used to infect target animals. The recombinant virus causes infection and replicates in the animal cells resulting in production of the recombinant cytokine. The infecting recombinant virus may subsequently be eliminated after production of an immunomodulatingly effective amount of the recombinant cytokine. A similar protocol is adopted with live bacterial carriers. Alternatively, a non-replicating, non-infectious viral vector may be used. A non-replicating viral vector provides a means of introducing a genetic sequence which is transiently capable of expression of the desired cytokine because the non-replicating viral vector is not capable of cell-to-cell transmission. The present invention provides an opportunity to enhance an immune response in animals and in particular poultry, domestic birds or game birds (such as those described above) by the administration of an avian cytokine, in particular a Type II interferon such as ChlFN-γ or a derivative thereof, either directly or via the expression of recombinant genetic sequences. This is of particular importance since most subunit and synthetic peptide vaccines are only weakly antigenic. The administration of the cytokines may be alone, in combination with an antigen or as a fusion molecule. Administration may be via an attenuated virus, recombinant viral vector or bacterial vector or may be by administration of the cytokine by, for example, injection or oral ingestion (e.g. in medicated foodstuff). The present invention extends to a veterinary pharmaceutical composition for use in poultry, domestic bird or game birds such as to enhance the immune system or accelerate its maturation or improve its immunocompetence or to facilitate immunomodulation in said birds, said composition comprising a recombinant avian Type II interferon or interferon-like molecule or a fusion molecule between a Type II interferon and a second cytokine fused to an antigen or genetic sequences encoding same and one or more carriers and/or diluents acceptable for veterinary use. Preferably, where the composition comprises a recombinant avian cytokine as hereinbefore defined, the composition is injected in ovo or post-hatching, or administered via aerosol or ingestion. Where the composition comprises genetic material, it is administered as part of a viral vector, bacterial vector or as a nucleic acid molecule. Conditions in poultry, domestic bird or game birds for which treatment might be required include infectious disease induced by any viral or bacterial agent such as those discussed supra, cancer, immunosuppression, allergy and to enhance or suppress reproductive systems. Conditions would also include situations where animals are in an immunocompromised state such as during or following stress, due to overcrowding and transport process, changes in climate. The bird to be treated and the cytokine in the composition might be "homologous" in the sense that both are of the same species, or may be "heterologous" where the avian cytokine is effective in another bird species than the species from which it has been derived. The compositions may also contain other active molecules such as antibiotics or antigen molecules. Combinations of cytokine molecules with antigen molecules may increase the efficacy of vaccines. The present invention, therefore, extends to a veterinary pharmaceutical composition comprising an immunomodulatingly effective amount of an avian Type II interferon or Type II interferon-like molecule or a fusion molecule between an avian Type II interferon or interferon-like molecule and a second cytokine or genetic sequences capable of expressing same and one or more carriers and/or diluents acceptable for veterinary use. In a preferred embodiment, said Type II interferon is IFN-γ, in particular ChlFN-γ. Wherein said pharmaceutical composition comprises a fusion molecule, said fusion is preferably a fusion between ChlFN-γ or a homologue, analogue or a derivative thereof and a second cytokine selected from the list comprising Type I interferons such as IFN- α, IFN-β, ChlFN-α, ChlFN-β or a Type II interferon or interferon-like molecule or any other cytokine or cytokine-like molecule. The active ingredient(s) of the pharmaceutical composition is/are contemplated to exhibit excellent activity in stimulating, enhancing or otherwise facilitating an immune response in an animal species and in particular a poultry, domestic bird or game bird when administered in an amount which depends on the particular case. The variation depends, for example, on the cytokine and, in some cases, the antigen involved in stimulating the immune response. For example, from about 0.5 μg to about 20 mg of a particular cytokine which may be combined with other cytokines, per kilogram of body weight per day may be required. Dosage regimen may be adjusted to provide the optimum therapeutic response. For example, several divided doses may be administered in one or more of daily, weekly or monthly or in other suitable time intervals or the dose may be proportionally reduced as indicated by the exigencies of the situation. The active compound may be administered by injection either in ovo or post-hatching or by oral ingestion in any convenient manner or may be administered via a genetic sequence si-ch as in a viral or bacterial vector. The active compounds may also be administered in dispersions prepared in glycerol, liquid polyethylene glycols, and/or mixtures thereof and in oils. Under ordinary conditions of storage and use, these preparations contain a preservative to prevent the growth of microorganisms. The pharmaceutical forms suitable for parenteral administration include sterile aqueous solutions (where water soluble) or dispersions and sterile powders for the extemporaneous preparation of sterile injectable solutions or dispersion. In all cases the form must be sterile and must be fluid to the extent that easy syringability exists. It must be stable under the conditions of manufacture and storage and must be preserved against the contaminating action of microorganisms such as bacteria and fungi. The carrier can be a solvent or dispersion medium containing, for example, water, ethanol, poiyol (for example, glycerol, propylene glycol, and liquid polyethylene glycol, and the like), suitable mixtures thereof, and vegetable oils. The proper fluidity can be maintained, for example, by the use of a coating such as lecithin, by the maintenance of the required particle size in the case of dispersion and by the use of surfactants. The prevention of the action of microorganisms can be brought about by various antibacterial and antifungal agents, for example, antibiotics, parabens, chlorobutanol, phenol, sorbic acid, thimerosal and the like. In many cases, it will be preferable to include isotonic agents, for example, sugars or sodium chloride. Prolonged absorption of the injectable compositions can be brought about by the use in the compositions of agents delaying absorption, for example. Sterile injectable solutions are prepared by incorporating the active compounds in the required amount in the appropriate solvent with various of the other ingredients enumerated above, as required, followed by filter sterilisation. Generally, dispersions are prepared by incorporating the various sterilised active ingredient(s) into a sterile vehicle which contains the basic dispersion medium and the required other ingredients from those enumerated above. In the case of sterile powders for the preparation of sterile injectable solutions, the preferred methods of preparation are vacuum drying and the freeze-drying technique which yield a powder of the active ingredient plus any additional desired ingredient from previously sterile-filtered solution thereof. Carriers and/or diluents suitable for veterinary use include any and all solvents, dispersion media, aqueous solutions, coatings, antibacterial and antifungal agents, isotonic and absorption delaying agents, and the like. The use of such media and agents for pharmaceutically active substances is well known in the art. Except insofar as any conventional media or agent is incompatible with the active ingredient, use thereof in the composition is contemplated. Supplementary active ingredients can also be incorporated into the compositions. The latter is particularly contemplated as far as the present invention extends to multivalent vaccines or multi-component cytokine molecules. The pharmaceutical veterinary compositions of the present invention may comprise in addition to an avian Type II interferon or interferon-like molecule or a fusion molecule comprising same, one or more other active compounds such as antigens and or immune stimulating compounds. The cytokine may also be delivered by a live delivery system such as using a bacterial expression system to express the cytokine protein in bacteria which can be incorporated into gut flora. Alternatively, a viral expression system can be employed or incoφorated into a recombinant vaccine. In this regard, one form of viral expression is the administration of a live vector generally by spray, feed or water where an infecting effective amount of the live vector (e.g. virus or bacterium) is provided to the animal. Another form of viral expression system is a non-replicating virus vector which is capable of infecting a cell but not replicating therein. The non-replicating viral vector provides a means of introducing genetic material for transient expression into a cytokine. The mode of administering such a vector is the same as a live viral vector. The cytokine molecule of the present invention, in particular ChlFN-γ, is also useful as a growth-enhancing or growth-promoting agent and/or maturation-promoting agent when administered to an avian species such as a species of poultry, domestic bird or a game bird. The present invention is particularly useful as a growth performance enhancer and, as the inventors have demonstrated in the Examples described herein, administration of ChlFN-γ to immature birds leads to significant increases in weight, addition to the prevention of weight loss usually associated with various disease states. Accordingly, a further aspect of the invention provides a method of enhancing growth performance of an avian species comprising administering to an avian a Type II interferon or interferon-like molecule. By enhancing growth performance is meant to increase the weight of an avian species or to prevent weight losses therein normally detectable during or following pathogenic infection of an avian species. Preferably, said Type II interferon molecule is IFN-γ. In a particularly preferred embodiment, said IFN-γ molecule is the ChlFN-γ molecule set forth in SEQ ID NO:2 or a homologue, analogue or derivative thereof. The avian species may be a healthy or diseased bird selected from the list comprising chickens, turkeys, bantams, quails, guinea fowl, ducks, geese, ostriches, emus, pigeons, canaries, budgerigars, parrots and finches, amongst others. Methods for the administration of the cytokine of the invention for the pmpose of promoting growth or enhancing growth of an avian species are similar to the methods discussed supra for the administration of a vaccine, adjuvant or veterinary pharmaceutical composition. The recombinant avian Type II interferon or interferon-like molecule of the present invention or a homologue, analogue or derivative thereof, in particular ChlFN-γ, is also useful in the production of immunological interactive molecules such as antibodies or functional derivatives thereof including Fabs or SCABS (single-chain antibodies), antibodies conjugated to an enzyme, radioactive or fluorescent tag, the only requirement being that said immunologically interactive molecules are able to bind to an avian Type II interferon or interferon-like molecule described herein. Accordingly, a further aspect of the present invention provides an immunologically- SUBSTTΓUTE SHEET (Rule 26) interactive molecule which binds to an avian Type II interferon molecule or y ς II interferon-like molecule, or a homologue, analogue or derivative thereof. Preferably, said avian Type II interferon or interferon-like molecule is IFN-γ. More preferably, said avian Type II interferon or interferon-like molecule is ChlFN-γ. In an even more preferred embodiment, said immunologically-interactive molecule binds to a Type II interferon or interferon-like molecule or a homologue, analogue or derivative thereof comprising at least 10 amino acid residues, preferably at least 20 amino acid residues and more preferably at least 50 amino acid residues contained within the amino acid sequence set forth in SEQ ID NO:2 or having at least 40% similarity thereto. In a most preferred embodiment, said immunologically interactive molecule is an antibody molecule. The antibody molecule may be monoclonal or polyclonal and may be used for developing eri--yme-immunosorbent assays for the rapid diagnosis of infectious diseases of poultry, domestic birds or game birds. According to this embodiment, there is provided an antibody preparation comprising antibodies or derivatives thereof, immunointeractive with either an avian Type II interferon or Type II interferon-like molecule or a derivative thereof or with a fusion molecule between an avian Type II interferon and a second cytokine. In a preferred embodiment, said Type II interferon is IFN-γ, in particular ChlFN-γ. Said second cytokine may be a Type I interferon molecule selected from the list comprising IFN-α, IFN-β, ChlFN-α, ChlFN-β or, alternatively, a Type II interferon other than ChlFN-α. Immunoassays are useful in detecting the presence of a cytokine in a target animal, particularly birds, in particular to detect an immune response in which the level of said avian cytokine is altered, for example following infection with a pathogen. As a consequence, such an immunoassay is of particular use in determining whether a bird has been exposed to a pathogen or is currently infected with a pathogen or has a prolonged low-grade pathogenic infection. Immunoassays are also useful for the quantitation of cytokines, in particular for screening genetic stocks for high cytokine- expressing lines with improved disease-resistance to a pathogen. The invention described herein extends to all such uses of immunointeractive molecules and diagnostic assays which require said immunoassays for their performance. A wide range of immunoassay techniques may be such as those described in US Patent Nos. 4,016,043, 4,424,279 and 4,018,653. These methods may be employed for detecting a Type II interferon or interferon-like molecule related to ChlFN-γ. By way of example only, an antibody raised against ChlFN-γ is immobilised onto a solid substrate to form a first complex and a biological sample from an animal to be tested for the presence of cytokine brought into contact with the bound molecule. After a suitable period of incubation, for a period of time sufficient to allow formation of an antibody-cytokine secondary complex, a second ChlFN-γ antibody labelled with a reporter molecule capable of producing a detectable signal is then added and incubated, allowing sufficient time for the formation of a tertiary complex of antibody-cytokine- labelled antibody. Any unreacted material is washed away, and the presence of the tertiary complex is determined by observation of a signal produced by the reporter molecule. The results may either be qualitative, by simple observation of the visible signal or may be quantitated by comparison with a control sample containing known amounts of hapten. Variations of this assay include a simultaneous assay, in which both sample and labelled antibody are added simultaneously to the bound antibody, or a reverse assay in which the labelled antibody and sample to be tested are first combined, incubated and then added simultaneously to the bound antibody. These techniques are well known to those skilled in the art, and the possibility of minor variations will be readily apparent. The antibodies used above may be monoclonal or polyclonal. The solid substrate is typically glass or a polymer, the most commonly used polymers being cellulose, polyacrylamide, nylon, polystyrene, polyvinyl chloride or polypropylene. The solid supports may be in the form of tubes, beads, discs or microplates, or any other surface suitable for conducting an immunoassay. The binding processes are well-known in the art and generally consist of cross-linking covalently binding or physically adsorbing the molecule to the insoluble carrier. By "reporter molecule", as used in the present specification, is meant a molecule which, by its chemical nature, produces an analytically identifiable signal which allows the detection of antigen-bound antibody. Detection may be either qualitative or quantitative. The most commonly used reporter molecule in this type of assay are either enzymes, fluorophores or radionuclide containing molecules (i.e. radioisotopes). In the case of an enzyme immunoassay, an enzyme is conjugated to the second antibody, generally by means of glutaraldehyde or periodate. As will be readily recognised, however, a wide variety of different conjugation techniques exist which are readily available to one skilled in the art. Commonly used enzymes include horseradish peroxidase, glucose oxidase, β-galactosidase and alkaline phosphatase, amongst others. The substrates to be used with the specific enzymes are generally chosen for the production, upon hydrolysis by the corresponding enzyme, of a detectable colour change. It is also possible to employ fluorogenic substrates, which yield a fluorescent product. Alternatively, fluorescent compounds, such as fluorescein and rhodamine, may be chemically coupled to antibodies without altering their binding capacity. When activated by illumination with light of a particular wavelength, the fluorochrome-labelled antibody adsorbs the light energy, inducing a state of excitability in the molecule, followed by emission of the light at a characteristic colour visually detectable with a light microscope. As in the EIA, the fluorescent labelled antibody is allowed to bind to the first antibody-hapten complex. After washing off the unbound reagent, the remaining complex is then exposed to the light of the appropriate wavelength, the fluorescence observed indicates the presence of the hapten of interest. Immunofluorescence and EIA techniques are both very well established in the art and are particularly preferred for the present method. However, other reporter molecules, such as radioisotope, cherniluminescent or bioluminescent molecules, may also be employed. It will be readily apparent to the skilled technician how to vary the procedure to suit the required purpose. The immunologically-interactive molecule is also useful in purifying the recombinant avian cytokine of the present invention. Methods for the affinity purification of proteins using antibodies are well-known to those skilled in the art. The present invention is further described by reference to the following non-limiting Figures and Examples. In the Figures: Figure 1 is a graphical representation showing sensitivity of chicken IFN to heat and low pH treatment. Supernatant from CEF cultured for 24 hr with Semliki Forest virus was used as a source of IFN-β. Adherent (spleen cells depleted of non-adherent cells), non-adherent (spleen cells depleted of plastic-adherent cells) and whole (unseparated spleen cells), spleen cell populations were cultured for 24 hr with concanavalin A (ConA). Supematants were heated to 60°C for 1 hr, exposed to pH2 for 8 hr or kept at 4°C (control) and then assayed for IFN activity using the CEF assay as described. Figure 2 is a graphical representation showing sensitivity of IFN activity to heat. Supematants from ConA activated spleen cells were heated for up to 1 hr as indicated and then tested for activity in the CEF assay. Figure 3 is a graphical representation showing the ability of supematants from the CC8.1 T cell line (AGAL Accession No. N94/46035) to protect CEF from virus mediated lysis and their ability to induce HD11 cells to secrete nitrite. Figure 4 is a graphical representation showing sensitivity of ChlFN-γ activity to heat. Supematants from CC8.1h (AGAL Accession No. N94/46035) and ConA activated spleen cells (CS) were heated to 60°C for various periods of time. Residual (heat resistant) IFN activity was measured using the CEF assay. Figure 5 is a graphical representation showing sensitivity of ChlFN-γ activity to heat, pH 2.0 and 2-mercaptoethanol (2-ME). Supematants from the CCδ.lh (AGAL Accession No. N94/46035) was heated to 60°C for 1 hr, exposed to pH 2.0 for 8 hr or exposed to 0.5% 2-ME or the combinations of these conditions indicated. Residual activity was measured using the CEF assay. Figure 6 is a graphical representation showing induction of nitrite secretion by HD11 macrophages induced by T cells expressing ChlFN-γ. Supe atants from native or heat- inactivated CC8.1h (AGAL Accession No. 94/46035) or SFV-induced CEFs were measured for their ability to induce nitrite secretion. Figure 7 is a graphical representation showing heat sensitivity of nitrite-inducing (ChlFN-γ) activity. Supematants from CC8.1h (AGAL Accession No. N94/46035) and ConA activated spleen cells were heated to 60°C and residual ChlFN-γ activity was measured using the nitrite assay as described in the Examples. Figure 8 provides graphical representations showing biological activity of supematants from transfected COS cells. COS cells were transfected with pools of approximately 100 clones from the CCS. lh cDNA expression library. ChlFN-γ was measured in the CEF assay (Figure 8A) or the nitrite assay (Figure 8B) as described in the Examples. Supernatant from COS cells expressing the ChlFN-γ gene was heated at 60°C for 30 min (148 heat) or not heated (148). Supernatant from CC8.1h was used as a positive control and supernatant from COS cells transfected with a pool lacking the ChlFN-γ gene (58) was used as a negative control. Figure 9 is a graphical representation showing biological activity of supematants from COS cells transfected with single clones of the CC8.1h library. Plasmid pools containing 100 clones were sequentially subpooled into pools of 10 and then into single clones. Clones 148.1.7 and 148.1.9 were transfected into COS cells and ChlFN-γ activity was measured in the supernatant 3 days later. The effect of heating the recombinant ChlFN-γ to 60°C for 30 min is shown. Figure 10 is a graphical representation showing production of recombinant ChlFN-γ. COS cells were transfected with #148 (pool of 100 clones), #148.1 (a pool of 10 clones derived from 148) and #148.1.9 (a single clone derived from 148.1). Supernatant from CC8.1h (AGAL Accession No. N94/46035) is used as a positive control. The effect of heating the supematants to 60°C for 30 min is also shown. Figure 11 is a graphical representation showing heat sensitivity of ChlFN-γ. Supernatant from CC8.1h (AGAL Accession No. N94/46035) or clone 148.1.9 was heated to 60°C for various periods of time and residual ChlFN-γ activity was measured in the nitrite assay. Figure 12 is a diagrammatic representation showing the nucleotide sequence of the ChlFN-γ cDNA with the predicted 164 amino acid sequence of the ChlFN-γ polypeptide shown. Two potential N-Iinked glycosylation sites are underlined. The predicted cleavage site for the mature protein is indicated by the arrow at HIS 1. Figure 13 is a diagrammatic representation showing amino acid sequence homology between the ChlFN-γ polypeptide (avian) and various mammalian IFN-γ proteins. Amino acids conserved in all species are highlighted by asterisks and conservative substitutions by dots. Figure 14 is a diagrammatic representation showing amino acid sequence homology between human and avian IFN-γ polypeptides. Figure 15 is a diagrammatic representation showing a comparison of ChlFN-α (Sekellick et al, 1994) and ChlFN-γ protein sequences. Figure 16 is a graphical representation showing cross-species biological activity of ChlFN-γ, bovine IFN-α and bovine Ii-Nγ. Recombinant chicken and bovine IFNs were β ayed for their ability to protect chicken and bovine fibroblasts from virus mediated lysis. Figure 17 provides graphical representations of F ACS profiles showing the expression of Class II antigen by HD11 cells. Cells were cultured in media alone (Figure 17A), LPS (Figure 17B), native ChlFN-γ (supernatant from CC8.1h; Figure 17C) and recombinant ChIFN-γ_(Figure 17D) and then measured for cell surface expression of Class II molecules. Figure 18 provides diagrammatic representations of polyacrylamide gels showing expression of recombinant ChlFN-γ in E. coli and subsequent purification. In Figure 18 A: S, standard Mr markers; Lane 1, crude sonication supernatant; Lane 2, soluble fraction; Lane 3, Ni column flow through; Lane 4 and 5, column washes; Lane 6, eluted recombinant ChlFN-γ. In Figure 18B: S, standard Mr markers; Lanes 1-4, purified recombinant ChlFN-γ serially diluted 2-fold (lane 1), 4-fold (lane 2), 8-fold (lane 3) or 16-fold (lane 4). Figure 19 provides graphical representations showing biological activity of recombinant ChlFN-γ on chicken (CEF) and turkey cells (TEF). In Figure 19A the capacity of purified recombinant ChlFN-γ (ED: dialyzed to remove imidazole; E: non-dialyzed), to induce nitrite secretion by HD11 chicken macrophages is shown. In Figure 19B; the capacity of purified recombinant ChlFN-γ (ED: dialyzed; E: non-dialyzed) and chicken spleen cell conditioned media (CM) to protect CEFs from virus mediated lysis is shown. In Figure 19C, the capacity of purified recombinant ChlFN-γ (ED: dialyzed; E: non- dialyzed) and recombinant ChlFN-α to protect TEFs from virus mediated lysis is shown. Figure 20 is a graphical representation showing stability of recombinant ChlFN-γ following storage at room temperature [6.2D (RT)] or at 4°C (6.2D) as measured using the nitrite assay. Figure 21 is a diagrammatic representation of a Western Blot showing binding of rabbit anti-ChlFN-γ sera to recombinant ChlFN-γ. Recombinant ChlFN-γ was electrophoresed on an acrylamide gel, blotted onto nitrocellulose which was then cut into strips. Individual strips were incubated in sera; (76 P/B, normal rabbit serum; ITA, serum raised against an irrelevant antigen; 76.79 sera from 4 rabbits immunized with recombinant ChlFN-γ). Figure 22 provides graphical representations showing the ability of rabbit anti- recombinant ChlFN-γ antisera to block the function of both recombinant (r) and native (n) ChlFN-γ as measured using either the nitrite assay Figures 22A, 22B) or using the CEF assay (Figure 22C). Figure 23 provides graphical representations showing the ability of mouse anti- recombinant ChlFN-γ antisera (Figure 23A) and purified rabbit anti-recombinant ChlFN- γ IgG (Figure 23B) to block the function of native ChlFN-γ in the nitrite assay. Figure 24 provides graphical representations showing the ability of ChlFN-γ and ChlFN-α to synergise. In figure 24A, the IFN activity is deteimined using the CEF assay. In Figure 24B and 24C, IFN activity is measured using the nitrite assay. Recombinant ChlFN-γ was serially diluted in the presence of limiting amounts of recombinant ChlFN-α or natural ChlFN-β. Figure 25 is a graphical representation showing the effect of recombinant ChlFN-γ treatment in vivo on the antibody response to SRBC. Groups of birds were injected with 200 μl (Groups 1 and 2) or 20 μl (Groups 3 and 4) of SRBC and re-immunised after 3 weeks. Groups 1 and 3 were treated with recombinant ChlFN-γ (on the day before, on the day of, and on the day after primary immunisation) and Groups 2 and 4 were not treated. HA titres for total lg and for IgG (2 mercaptoethanol-resistant lg titres) were determined weekly for 6 weeks. A, Togal lg HA titres 3 weeks after the primary immunisation; B, Total lg HA titres 3 weeks after secondary immunisation; C, Total lg HA titres (there are significant differences between Group 1 and 2 and between Group 3 and 4: *p<0.02, **p<0.05, ***p<0.005, ****p<0.002); D, IgG HA titres. Figure 26 is a graphical representation showing the effect of recombinant ChlFN-γ treatment in vivo on weight gain. Birds were injected with recombinant ChlFN-γ or with diluent and their body weight was monitored. Figure 27 provides graphical representations showing the effect of recombinant ChlFN-γ treatment in vivo on weight gain. Birds were injected with recombinant ChlFN-γ or with diluent and their body weight was determined at days 6 (Figure 27A) and 12 (Figure 27B). Weight gain between days 6 and 7 is shown in Figure 27C and between days 7 and 10 is shown in Figure 27D. Figure 28 provides graphical representations showing the effect of recombinant ChlFN-γ treatment in vivo on weight gain during infection with E. acervulina. Birds were injected with recombinant ChlFN-γ or with diluent, infected with E. acervulina oocytes and their body weight was deteπnined at days 8 (Figure 28A) and 11 (Figure 28B). Changes in weight between days 4 and 5 is shown in Figure 28C and between days 6 and 8 is shown in Figure 28D. Figure 29 is a graphical representation showing the effect of recombinant ChlFN-γ treatment in vivo on weight gain in non-infected birds and those infected with coccidiosis. Figure 30 is a graphical representation showing the effect of recombinant ChlFN-γ treatment in vivo on the ratio of bursa to body weight 7 days following infection with IBDV. Figure 31 is a graphical representation showing the effect of recombinant ChlFN-γ treatment in vitro on the ability to protect CEFs from infection with IBDV. CEFs were prepared as described for the CEF interferon assay. Recombinant ChlFN-γ and IBDV were added to the cultures together. Cell survival was measured 3 days later on a scale of 0 to 4, where 0 represents the level of cell survival observed in the presence IBDV and the absence of IFN (< 5% cell survival) and 4 represents the level of cell survival observed in the absence of IBDV (> 90 % cell survival). SUBSITTUTE SHEET (Rule 26 EXAMPLE 1 Chickens Specific Pathogen Free (SPF) Hybrid White Leghorn (HWL) chickens produced by the CSIRO SPF poultry unit (Maribymong, Victoria) were raised in flexible plastic isolators and fed fumigated feed and acidified water. EXAMPLE 2 Cell cultures Spleens were aseptically removed from chickens and single cell suspensions were centrifuged for 5 min at 200g. Cells were washed twice in Hanks' balanced salt solution (Flow Laboratories) and resuspended in growth medium consisting of DME medium (Flow) containing penicillin, streptomycin, 2mM glutamine and buffered (pH 7.2) with HEPES and sodium bicarbonate. Cells were incubated at 41 °C in 5% CO2 • 7 in air. Conditioned medium was prepared by culturing spleen cells (1 x 107ml) under serum-free conditions in the presence of Concanavalin A (ConA, 5 ug ml, Sigma). Supematants were collected after 24 hr, centrifuged to remove cell debris and stored at 4°C. Adherent spleen cells were obtained by incubating whole spleen cell populations in plastic petri dishes in growth media at 41 °C. After 4-8 hr, non-adherent cells were removed and the plates were washed once. EXAMPLE 3 Generation of T cell lines REV-transformed T cell lines were generated from spleen as previously reported (Lowenthal et al 1995a, 1995b). Cells were cultured in Hahns' medium containing 1% chicken serum and 5% FBS for several days and their supernatants were assayed for interferon activity. Actively growing cell lines were stained with anti-T cell monoclonal antibodies (Mabs) CD3, CD4, CD8 and analysed by llow cytometry. Cell clones were obtained by c turing single cells in wells of 96 well microtiter plates. Actively growing clones were tested for IFN production and stained with T cell Mabs and analysed as above. Non-transformed ConA activated spleen cells failed to grow for more than 7 days and could not be cloned from single cells. EXAMPLE 4 Chicken embryonic fibroblast (CEF) interferon assay IFN was measured by the ability to protect CEF and turkey embryonic fibroblasts (TEF) from virus-mediated as described by Prowse and Pallister (1989), Lowenthal et al (1995a) and Lowenthal et al (1995b). Secondary fibroblasts were seeded into 96 well microtiter plates (5 x 10 /well) and grown in the presence of 10% FBS at 41°C. After 24 hr the culture medium was replaced with 100 μl of serum-free growth medium and 2-fold serial dilutions of test supematants were made in duplicate. Control wells contained cells cultured in medium alone or cultured in the presence of a reference supernatant of known IFN activity. After overnight incubation at 37°C, the culture medium was replaced with 100 μl of medium containing Semliki Forest virus or Vesicular Stomatitis virus (10 3 tissue culture infective dose / ml) and the cells were incubated at 37°C. After 24 hr, cell viability was measured by uptake of neutral red dye and absorbance at 540 nm was quantitated using an ELISA reader. EXAMPLE 5 Treatment of IFN Supematants were heated at 60 β C in Eppendorf tubes for various periods of time and immediately placed on ice. Supematants were exposed to low pH treatment as follows: a sufficient quantity of 2M HC1 was added to attain a pH of 2.0. After 8 hr at 4°C, the pH was adjusted to pH7.0 using 5M NaOH. Sensitivity of IFN to reducing agents was measured by adding 0.5% (V/V) 2-mercaptoethanol (2-ME) to supematants. All supe atants were then stored at 4°C. EXAMPLE 6 Nitrite assay Production of nitric oxide by HD11 chicken macrophages (Beug et al, 1979) was quantitated by accumulation of nitrite in the culture medium (Sung et al, 1991) and was used as a measure of IFN-γ activity . Two-fold serial dilutions of test supematants were made in duplicate wells of 96 well plates in a volume of 100 μl of growth medium containing 5% FBS. HD11 cells were added to each well (10 5 in 100 μl) and the plates were incubated at 37°C. After 24 hr, 50 μl of culture supernatant was added to 100 μl of Griess reagent (1:1 mixture of 1% sulfanilamide and 0.1% naphthylethylene diamine in 2.5% H3PO4) and absorbance was read at 540 nm. The level of nitrite was determined using sodium nitrite as a standard. EXAMPLE 7 cDNA library production and transfection of COS cells PolyA + RNA from the CC8.1h T cell clone (AGAL Accession No. N94/46035) was directionally cloned into the eucaryotic expression vector pcDNAI (Clontech, Palo Alto, CA). Pools of 100 clones were transfected into COS cells by the DEAE-dextran method as follows: 1 μg of DNA was mixed with 10 μl of DEAE-dextran (10 mg/ml, Sigma) and added to 1 X 10 6 cells in 0.5 ml of media containing 1% FBS. Cells were incubated in Eppendorf tubes at 37°C. After 30 min, 0.5 ml of 25% (v/v) DMSO in DME was added and mixed. After 5 min the cells were washed in media and resuspended in 5 ml of DME with 2% FBS and cultured for 3 days at 37°C. Supematants were tested for IFN activity as described in Example 4 and Example 6. E. coli were then transformed with positive plasmid pools and new plasmid preparations were made from pools of 10 individual colonies. COS cell transfection and supernatant screening was repeated and positive pools were identified. The process was repeated until single positive clones were isolated. The insert was subcloned into Bluescript IKS and the nucleotide sequence of both strands was determined using an automated gene sequencer. EXAMPLE 8 Expression of ChlFN-γ in E coli. The mature coding region of ChlFN-γ was cloned into the pQE expression vector {QIAexpress Type IV construct, Qiagen, CA) according to manufacturers instructions. The sequence of the oligonucleotides used to PCR the mature region of the gene is as follows: sense 5' ACTAGATCTCATACTGCAAGTCTAAAT 3' antisense 5' ACTAAGCTTTTAGCAATTGCATCTCCTCTG 3' All procedures used for the expression of recombinant ChlFN-γ using Ni columns and purification was according to manufacturers instructions. EXAMPLE 9 Preparation of antibodies to ChlFN-γ Rabbit antisera was raised against purified recombinant ChlFN-γ protein. Rabbits were immunized three times with 400 μg of protein and sera was collected 10 days after the final injection. Specific reactivity of the sera to ChlFN-γ was confirmed using immune and pre-immune sera in Western blots and in assays measuring the ability to inhibit the release of nitrite by HD11 cells. Monoclonal antibodies (Mabs) were raised by immunising mice 4 times with 10 μg of recombinant ChlFN-γ and screening was performed using Western blots. EXAMPLE 10 Expression of Class II molecules HD11 cells were cultured at 41 °C in the presence of recombinant and native ChlFN-γ for 48 hrs and were then analysed for the cell surface expression of Class II. Cells were washed twice and incubated for 20 min with monoclonal anti-Class II antibody (MUI 78 ) followed by incubation with FITC-sheep anti-mouse lg (Fab 2). They were then washed three times and fixed by resuspending in PBS containing 1% paraformaldehyde. Cell suspensions were analysed using a FACScan (Becton Dickinson, Mountain View, CA). with a total of 10 4 cells analysed for each sample. EXAMPLE 11 ChlFN-γ as an adjuvant Four Groups (n = 10) of 3-week old SPF chickens were injected intramuscularly with either 0.2 or 0.02 ml of sheep red blood cells (SRBC). One group at each dose was also injected intra-peritoneally with 500 Units of recombinant ChlFN-γ the day before and on the day of immunization. Birds were bled weekly and haemaglutination titres of the sera were determined. EXAMPLE 12 Effect of recombinant ChlFN-γ on infection with Infectious Bursal Disease Virus in vivo One group (n = 10) of three-week old SPF chickens was injected intraperitoneally with 500 Units of recombinant ChlFN-γ on 2 consecutive days and another group of control birds (n =10) was injected with diluent alone. Both groups of birds were infected intra- ocularly with Infectious Bursal Disease Virus (IBDV). Birds were sacrificed 7 days later and the bursa and whole body weights were determined. EXAMPLE 13 Production of IFN Spleen cells were cultured at 41 °C in the presence of a variety of mitogens and the supematants were tested after 24 hr for the presence of IFN activity using the CEF assay. The results are summarized in Table 2. Preliminary experiments showed that olturing the cells at 41°C resulted in approximately 5-fold higher levels of interferon compared to 37°C. The optimal cell concentration was 5 X 10 6 leukocytes/ml. Kinetic experiments revealed that IFN was first detected 4 hr after stimulation and reached maximal levels at 24 hr (data not shown). Recombinant IFN (-α, -β or -γ) from human, murine, bovine, avian and porcine species were all inactive in the CEF assay at concentrations of up to 10 U/ml ( Digby and Lowenthal, 1995). EXAMPLE 14 Characterisation of IFN types Supematants collected from CEF infected with Semliki Forest virus were used as a source of IFN-β (Sekellick and Marcus, 1986) and treated as described in Example 5. In agreement with previously published results (von Bulow et al, 1984; Thacore et al, 1985) interferon produced by CEF is resistant to heating at 60°C and to pH2.0 treatment (Fig. 1). Spleen cell populations were either enriched for adherent cells (mostly monocytes), enriched for non-adherent cells or left as whole spleen populations. IFN production was induced by culturing the cells for 24 hr in the presence of ConA or LPS. Approximately 95% of the IFN activity produced by adherent cells was resistant to heating at 60°C for 1 hr and exposure to pH2.0 (Fig. 1), consistent with IFN-α/β activity. In contrast, only 25% of the IFN activity produced by ConA activated non- adherent spleen cells was resistant to heat or pH2.0 treatment. These results indicate that this T cell-enriched population produced predominantly IFN-γ, but that a significant amount of IFN-α/β is also present. Whole spleen populations produced a mixture of resistant and labile IFN. Supernatants from whole spleen cell populations were heated for various periods of time as described in Example 5 and subsequent loss of IFN activity was measured. Kinetic experiments confirmed that supernatants from ConA induced whole spleen cell populations (CS) contained a mixture of heat-sensitive and heat-resistant IFN. About 60% of IFN activity was lost within 1-2 min of heating to 60°C while the resistant fraction lost activity much more slowly with a half-life of >2 hr (Fig. 2). Exposure to higher temperatures increased the rate of loss of activity fur the resistant but not the sensitive IFN. EXAMPLE 15 Production of chicken T cell lines The phenotype of some representative REV-transformed chicken T cell lines are shown in Table 3. Supernatants from these cell lines were measured for the presence of IFN-γ. The CC8.1 cell line and its clones were found to produce high levels of IFN activity (Table 3). Clones were analysed 7-8 days after cloning and were clearly positive for CD3 and CD4 surface markers. Clones kept continuously in culture for 6 months continued to secrete high levels of IFN-γ. We refer to this type of IFN as chicken IFN- γ (ChlFN-γ) ChlFN-γ production is constitutive because exposure of these cell lines to various stimuli (ConA, PHA, CD3 Mabs, TCR Mabs or combinations of these) increased ChlFN-γ levels by less than 2-fold (Table 2). Several clones were obtained from the CC8.1 cell line and were measured for their ChlFN-γ production using the CEF assay described in Example 4 or the nitrite assay described in Example 6. There was a considerable variation in the amount of ChlFN-γ produced by individual clones, however, the ratio of IFN titer as measured in the CEF assay to that of the nitrite-inducing activity remained constant (Fig. 3). When ChlFN-γ present in the supernatant from a chicken T cell clone (CCδ.lh) was heated to 60°C it was shown to be labile. (Fig. 4). EXAMPLE 16 Characterisation of ChIFN-7 In order to further characterize ChlFN-γ produced by chicken T cells, supernatants from CC8.1h were treated in various ways including exposure to pH2 and 2-ME as described in Example 5. The majority ( - 80%) of the ChlFN-γ activity was sensitive to either heat or pH2 treatment when measured in the CEF assay as described in Example 4 (Fig. 5). The combination of heat and pH2 treatment did not result in a further loss of activity. The majority of ChlFN-γ activity also was resistant to exposure to 2-ME and this 2-ME-resistant IFN was heat-labile. The properties of ChlFN-γ is highly consistent with the physio-chemical profile reported for mammalian IFN-γ. In mammals, IFN-γ can be distinguished from IFN-α/β by its ability to stimulate nitrite production by macrophages. In order to confirm that this also held true for ChlFN-γ, T cell supematants were assayed for their ability to induce HD11 macrophages to produce nitrite. CC8.1h supernatant contains approximately 2400 U/ml of IFN activity when measured by the CEF assay (Example 4) and 640 U/ml of IFN as measured by the nitrite assay (Example 6). When heated for 30 min at 65°C, the IFN titer of this supernatant was reduced to 10 U/ml (Fig. 6), indicating that the heat labile ChlFN-γ was responsible for the nitrite-inducing activity. On the other hand, supernatants with 4000 U/ml of IFN-β (as measured by the CEF assay of Example 4) contain only low levels of nitrite-inducing activity which is not heat labile (Fig. 6). Furthermore, the nitrite- inducing activity produced by these T cells was found to be heat-labile, with ~ 90% of the activity lost within 5 min of heating to 60°C (Fig. 7). These results indicate that avian IFN-β, like its mammalian counteφart, is very inefficient in inducing nitrite secretion when compared to IFN-γ. Table 4 summarizes the production of IFN by CEF and CC8.1h T cells. It compares the CEF IFN titers and the nitrite-inducing titers for supematants of both cell types. The ratio of CEF to nitrite titers for T cell-derived ChlFN-γ is 5 compared to 480 for CEF derived IFN-β. This result is consistent with that found in mammals where IFN-γ is superior to IFN-β in its ability to induce nitrite secretion. EXAMPLE 17 Identification of the ChlFN-γ gene. A cDNA expression library was generated from the CC8.1h chicken T cell line as described in Example 7. Pools of 100 cDNA clones were transfected into COS cells and supernatants were tested for IFN bioactivity 2 to 4 days later. Several supernatants were found to be active in both the CEF (Fig. 8A) and nitrite (Fig. 8B) assays. The IFN activity was sensitive to heat and pH 2 treatment, indicating the presence of a functional IFN-γ gene in the plasmid pool. Positive pools were individually transformed into E. coli and plasmid preparations were generated from pools of 10 clones. Several of these plasmid pools were positive for the IFN-γ gene and the process was repeated until single positive clones (eg. 148.1.7 and 148.1.9) were isolated (Fig. 9). EXAMPLE 18 Characterization of recombinant ChlFN-γ. COS cells transformed with plasmid preparations from individual positive clones produced very high levels of recombinant ChlFN-γ (Fig. 10). Recombinant ChlFN-γ showed the same degree of heat sensitivity (Fig. 11) and pH 2 sensitivity (data not shown) as that shown by natural ChlFN-γ. Nucleotide sequences of several cDNA clones were determined as described in Example 7 and found to be identical. The ChlFN-γ nucleotide and derived amino acid sequences are shown in Fig. 12 and SEQ ID Nos: 1 and 2. The ChlFN-γ cDNA codes for a predicted protein of 164 amino acids with a signal peptide of 19 amino acids. The predicted mature protein is 145 amino acids in length with a molecular mass of 16.8 kD. Two potential N-glycosylation sites are predicted, the most likely site is at position 42- 44, with the other at position 23-25. Like other IFN-γ proteins, ChlFN-γ contains few cysteine residues. The mature protein has only two cysteines which are located at the C-teπninus (Fig. 12). EXAMPLE 19 Comparison to mammalian IFN-γ. Comparison of the predicted amino acid sequence of ChlFN-γ to a number of mammalian IFN-γ protein sequences revealed that although the sizes are similar, the overall level of homology is relatively low (Fig. 13). When compared to a single mammalian species the ChlFN-γ protein shows a higher degree of amino acid identity (it is 32% identical to human IFN-γ) and several highly conserved short sequences are evident (Fig. 14). ChlFN-γ shares a low degree of identity (15%) with ChlFN-α as shown in Fig.15. Furthermore, recombinant ChlFN-γ did not protect bovine fibroblasts from virus mediated lysis and likewise bovine IFN-α and -γ failed to protect CEF (Fig. 16). EXAMPLE 20 Expression of Class II molecules. HDl l cells cultured in the presence of recombinant or native ChlFN-γ for 48 hr as described in Example 10 showed enhanced levels of cell surface expression of Class II molecules relative to cells grown in media alone (88% and 52% increase in expression, respectively). In contrast, the presence of another macrophage stimulator, LPS, induced only an 8% increase in Class II expression (Fig. 17). EXAMPLE 21 Expression of recombinant ChIFN-γ in E coli. and biological function. Recombinant ChlFN-γ (r ChlFN-γ) bearing a poly-HIS tag was expressed in E coli using the pQE expression system and purified using a Ni affinity column (Fig. 18A). Two forms of recombinant ChlFN-γ were produced (Mr 16 and 18 kDa). The activity of recombinant ChlFN-γ was deteπriined using the CEF assay (Example 4), nitrite assay (Example 6) or a Turkey Embryonic Fibroblast (TEF) protection assay. Recombinant ChlFN-γ was active in the nitrite assay (Fig. 19A), in the CEF assay (Fig. 19B) and in a Turkey TEF protection assay (Fig. 19C). The stability of recombinant ChlFN-γ was also monitored over various time intervals. Data provided in Figure 20 indicate that recombinant ChlFN-γ is stable when stored at 4°C or at room temperature. The inventors have shown further that recombinant ChlFN- γ can be stored for several months. Antisera to recombinant ChlFN-γ were raised in 4 rabbits as described in Example 9. Sera from each rabbit recognised recombinant ChlFN-γ as shown by Western blots (Fig. 21). Some of these rabbit sera also inhibit the biological function of native and recombinant ChlFN-γ in vitro but did not block the function of ChlFN-β (Fig. 22). Mice were also immunised with recombinant ChlFN-γ as described in Example 9 and there sera were found to inhibit the ability of ChlFN-γ to induce nitrite secretion by HDl l cells (Fig. 23 A). Furthermore, protein G-purified rabbit anti-recombinant ChlFN-γ antibodies also inhibit the function of recombinant ChlFN-γ (Fig. 23 B). EXAMPLE 22 Synergy between type I and type II ChlFNs ChlFN-γ shows synergy with ChlFN-α and ChlFN-β in both the CEF and nitrite assays. CEFs were cultured in the presence of ChlFN-γ that had been serially diluted in a limiting amount of recombinant ChlFN-α. The combination of the two IFNs was up to 5 times more effective than either type of IFN alone (Fig. 24A). A similar level of synergy was shown in the nitrite assay (Fig. 24B). Native ChlFN-β was also able to synergise with ChlFN-γ (Fig. 24C). EXAMPLE 23 ChIFN-7 as an adjuvant Chickens were injected with SRBC (with or without recombinant ChlFN-γ) and weekly haemaglutination (HA) titres of the sera were determined as described in Example 11. Results are shown in Figure 25. Treatment with recombinant ChlFN-γ resulted in a higher mean HA titre, a prolonged antibody response and increased the effectiveness of the low dose of antigen. This indicates that recombinant ChlFN-γ is an effective adjuvant. SUBSTITUTE SHEET (RULE 26; EXAMPLE 24 Effect of ChlFN-γ on weight gain One group (n = 10) of one-day old SPF chickens was injected intraperitoneally with 500 Units of recombinant ChlFN-γ on 2 consecutive days and another group of control birds was injected with diluent alone. Birds were weighed over a 12 day period. Birds injected with recombinant ChlFN-γ displayed enhanced weight gain (Fig. 26 and 27). The increase in body weight was from 5.8 to 9.0% (Table 5). These data indicate that recombinant ChlFN-γ was effective in enhancing growth performance. EXAMPLE 25 Effect of ChlFN-γ on weight gain during infection with E. acervulina One group (n = 10) of one-day old SPF chickens was injected intraperitoneally with 500 Units of recombinant ChlFN-γ on 2 consecutive days (day 0 and day 1) and another group of control birds was injected with diluent alone. All birds were infected with 5 x 10 oocytes on day 1 and then weighed over a 12 day period. Birds injected with recombinant ChlFN-γ displayed enhanced weight gain (Fig. 28A and B). Infection with coccidiosis normally results in weight loss between day 4 and 6 of infection. Treatment with ChlFN-γ reduced the weight loss (Fig. 28C) and enhanced the rate of weight gain following natural recovery from infection (Fig. 28D). Treatment with ChlFN-γ resulted in a 7.3 to 12.5% increase in weight (Tables 6 and 7 and Fig. 29). This indicates that recombinant ChlFN-γ was effective in reducing the effect of coccidiosis on growth performance. EXAMPLE 26 Effect of recombinant ChlFN-γ on infection with Infectious Bursal Disease Virus SPF chickens were injected with either recombinant ChlFN-γ or diluent on 2 consecutive days and then infected with IBDV. 7 days later their bursa and whole body weights were determined as described in Example 12. Birds injected with recombinant ChlFN-γ displayed an enhanced ratio of body:bursa weight from a mean of 1.36 to 1.51 (Fig. 30), indicating that recombinant ChlFN-γ was effective in reducing virus growth in vivo. The effect of recombinant ChlFN-γ to protect CEFs from infection with IBDV in vitro was also measured. CEFs were prepared as described for the CEF interferon assay and recombinant ChlFN-γ and IBDV were added to the cultures together. Cell survival was measured 3 days later on a scale of 0 to 4, where 0 represents the level of cell survival observed in the presence IBDV and the absence of IFN (< 5% cell survival) and 4 represents the level of cell survival observed in the absence of IBDV (> 90 % cell survival). As shown in Fig. 31, recombinant ChlFN-γ was effective in protecting CEFs from infection with IBDV in vitro. In conclusion, recombinant ChlFN-γ has been shown to effective in the prevention of infection by IBDV both in vivo and in vitro. EXAMPLE 27 Discussion Previous studies in chickens have identified only Type I IFN and cast doubts over whether chicken T cells are able to produce Type II interferon molecules. The inventors have shown herein that chicken T cells produce the Type II interferon molecule, IFN-γ. The inventors further address the nature of T cell-derived IFN directly by generating novel chicken T cell lines that produce high levels of ChlFN-γ. Such T cell lines have not been previously reported. The presence of Type II IFN in avian species was supported herein by the suφrising finding that supernatants from these T cells are capable of inducing high levels of nitrite production by macrophages, a property of IFN-γ but not IFN-α/β in mammals (Fast et al, 1993; Huang et al, 1993). In mammals, IFN-α from different species share a high degree of homology which allows functional cross reactivity to occur between most species. Similarly, IFN-β from one species will often react with cells from another species. IFN-α and -β also share a significant degree of homology and it is likely that their genes originated from a single gene (Weissmann and Weber, 1986). In contrast, IFN-γ produced by chicken T cells fails to function lly cross react with mammalian cells. There is also only limited homology between avian IFN-γ (i.e. ChlFN-γ) and mammalian IFN-γ molecules (see below. A chicken homologue of the mammalian Type I IFN gene has been cloned from virus- induced primary chicken embryo cells aged in vitro. ChlFN-α was shown to lack nitrite-inducing activity. Furthermore, antibodies raised to this protein failed to inhibit the nitrite-inducing activity of supematants from ConA induced chicken spleen cell cultures. A novel chicken T cell clone (CC8.1h) was used to clone the gene for ChlFN-γ. ChlFN- γ is unrelated to ChlFN-α. ChlFN-γ induced high levels of nitrite production by macrophages, a property of IFN-γ but not IFN-α/β in mammals. In contrast, Schultz et al (1995) recently reported that recombinant ChlFN-α could not induce the secretion of nitric oxide from chicken monocytes. The ChlFN-γ gene codes for a predicted mature protein of 145 amino acids with a molecular mass of 16.8 kD. ChlFN-γ protein is only 35% and 32% identical to the equine and human IFN-γ molecules, respectively. A C-terminal Lys-Arg-Lys-Arg motif may represent the point of pH 2 sensitivity observed for ChlFN-γ. Furthermore, the ChlFN-γ protein shares only 15% identity with the recently reported ChlFN-α, which is similar to the level of homology found when mammalian Type I and II IFNs are compared. Furthermore, ChlFN-γ is smaller in size than ChlFN-α and contains only two rather than seven cysteine residues. In mammals, IFN-α proteins are highly conserved at the amino acid level, which allows functional cross reactivity to occur between a number of species. Similarly, IFN-β from one species will usually react with cells from another species. IFN-α and -β also share a significant degree of homology to each other and it is likely that their genes originated from a single ancestral gene. In contrast, the level of homology between different mammalian IFN-γ proteins is relatively low and as a consequence functional activity only rarely crosses the species barrier. The degree of homology between the ChlFN-γ polypeptide and mammalian IFN-γ polypeptides is only 32-35%. ChlFN-γ does not function on cells from mammalian species. However, the inventors have demonstrated herein that ChlFN-γ does react with cells from other avian species in particular to turkey cells. Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications, the invention also includes all of the steps, features, compositions and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations or any two or more of said steps or features. Table 2: Production of IFN by chicken spleen cells and T cell clones. Interferon titer (U/ml in CEF assay) Stimulus: None ConA PHA CD3 TCR2 TCR3 Spleen* < 5 340 360 220 270 60 CC4.1 b < 5 < 5 < 5 - - CC4.3 C 220 160 240 180 - CC8.1 b 480 640 640 560 480 640 CC8.1h d 2400 4800 3200 3200 2400 CC8.1x d 1800 . • Spleen cells were cultured for 24 hr as described with or without stimulus b REV transformed T cell line (CD3 + , CD4 + ) c REV transformed T cell line (CD3 + , CD8 + ) d Cloned line (from CC8.1)59 Table 3: Phenotype of REV-transformed chicken T cell lines. Cell line: CD3 a CD4 a CD8 a TCR b IFN 0 CC4.1 97 48 25 2 < 5 CC4.2 97 23 54 2 120 CC4.3 94 14 58 2 80 CC7.1 93 22 37 3 60 CC7.2 98 29 45 2 120 CC7.3 98 21 39 2,1 80 CC8.1 97 81 4 2,3 160 CC8.1x d 95 nd nd nd 320 CC8.1h e 0 0 0 nd 320 CC8.1x e 0 0 0 nd 280 Spleen 60 18 45 2 < 5 a Percent of cells positive for surface marker Predominant phenotype of T cell receptor (TCR1,2,3) c IFN titer of supernatant (Nitrite assay, U/ml) Cloned from CC8.1 and analyzed 7 days post cloning e Cloned from CC8.1 and analyzed 4 weeks post cloning Spleen leukocytes from a 6 week old chicken Table 4: Relationship between IFN titers measured by CEF assay versus nitrite assay CEF a Nitrite b CEF:Nitrite c CC8.1h 3200 d 640 5 CEF 4800 10 480 a IFN titer measured by the CEF assay IFN titer measured by the nitrite assay c Ratio of CEF titer to nitrite-inducing titer d IFN (U/ml) Table 5: Effect of recombinant ChIFN-7 on weight gain in broilers. Day Body weight (g) a % Increase recombinant ChIFN-y p Control 0 3 154.0 ± 18 143.5 ± 24 7.3 4 204.9 ± 23 188.2 ± 35 9.0 5 235.4 ± 26 217.0 ± 40 8.5 6 262.3 ± 28 244.3 ± 47 7.4 7 290.1 ± 30 269.5 ± 49 7.6 10 390.8 ± 39 360.1 ± 62 8.6 12 475.6 ± 43 449.5 ± 75 5.8 a Mean weight of chickens (n=10) ± standard deviation Birds injected intra peritoneal with 500 U of recombinant ChlFN-γ on days 0 and 1 c Birds injected intra peritoneal with diluent on days 0 and 1 Table 6: Effect of recombinant ChlFN-γ on weight gain in broilers following infection with E. acervulina. ___ Body wei Rht (tf > a % Increase recombinant ChlFN ■ γ b Control 0 4 198.7 ± 26 185.1 ± 30 7.3 5 195.2 ± 26 176.8 ± 29 10.2 6 202.2 ± 23 185.4 1 31 9.1 8 248.4 ± 35 220.9 ± 42 12.5 11 353.6 ± 52 315.6 1 56 12.0 a Mean weight of chickens (n=10) 1 standard deviation Birds injected intra peritoneal with 500 U of recombinant ChlFN-γ on days 0 and 1 and infected with 5X10^ oocysts on day 1 c Birds injected intra peritoneal with diluent on days 0 and 1 and infected with 5X105 oocysts on day 1 Table 7: Effect of recombinant ChlFN-γ on weight gain in broilers following infection with E. acervulina. Dav Body weieht {_.. Increase (er recombinant ChlFN- Y b Control 0 1-4 52.0 a 52.1 -0.1 4-5 -3.5 -8.3 4.8 5-6 7.0 8.6 -1.6 6-8 46.2 35.5 10.7 8-11 105.2 94.7 10.5 1-11 206.9 182.6 24.3 a Mean weight gain of chickens (n=10) 1 standard deviation between the indicated days b Birds injected intra Deritoneal with 500 U of recombinant ChlFN-γ on days 0 and 1 and infected with 5X10^ oocysts on day 1 0 Birds injected intra peritoneal with diluent on days 0 and 1 and infected with 5X10 oocysts on day 1 Increase in body weight due to recombinant ChlFN-γ REFERENCES 1. A ann and Brosius (1985).Gene 40, 183 2. Ausubel, F.M. et al. (1987) In: Current Protocols in Molecular Biology, Wiley Interscience (ISBN 047140338). 3. Beug, H. et al (1979). Cell 18, 375-390. 4. Digby, M.R. and Lowenthal, J.W. (1995). J. Interferon Cytokine Res. 15, 939- 945. 5. Dijkmans, R. et al (1990). Vet. Immunol. Immunopathol. 26, 319-332. 6. Fast, D.J. et al (1993). J. Interferon Res. 13. 271-277. 7. Huang, S. et al (1993). Science 259, 1742-1745. 8. Lillehoj, H.S. et al (1992). Poult. Sci. Rev. 4, 67-85. 9. Lowenthal, J.W. et al (1993). Immunol. Cell Biol. 72, 1 15-122. 10. Lowenthal, J.W. et al (1995a). In: Advances in Avian Immunology Research. (Eds. Davison T.F., Bumstead N. and Kaiser P.) Carfax, Oxford. ppl79- 186. 1 1. Lowenthal, J.W. et al (1995b). J. Interferon Cytokine Res. 15, 933-938. 12. Prowse, S.J. and Pallister, J. (1989). Avian Pathol. 18, 619-630. 13. Pusztai, R. et al ( 1986). A eta Virol. , 30, 131-136. 14. Sambrook, J. et al (1989). In: Molecular Clorύng: A Laboratory Manual. Cold Spring Harbor Laboratory Press. 15. Schultz, V.et al (1995). Eur. J. Immunol. 25, 847-851. 16. Sekellick, M.J. and Marcus, P.I. (1986). Methods Enzymol. 119, 1 15-125. 17. Sekellick, M.J.e/ al (1994). J. Interferon Res. 14, 71-79. 18. Shimatake and Rosenberg (1981) Nature 292, 128 19. Studier and Moffat (1986) J. Mol. Biol. 189, 1 13 20. Sung, Y.-J.et al (1991 ). J. Leukocyte Biol 50. 49-56. 21. Thacore, H.R. e/ σ/ (1985). Interferon Res. 5, 279-288. 22. Von Bulow, V. et al (1984). Avian Pathol. 13. 621-637. 23. Weiler, H. and Von Bulow, V. (1987). Avian Pathol. 16. 439-452. 24. Weissmann, C, and Weber, H. (1986). Prog. Nucleic Acid Res. 33, 251-300. SEQUENCE LISTING (1) GENERAL INFORMATION: (i) APPLICANT: Commonwealth Scientific and Industrial Research Organisation (ii) TITLE OF INVENTION: Novel avian cytokines and genetic sequences encoding same (iii) NUMBER OF SEQUENCES: 2 (iv) CORRESPONDENCE ADDRESS: (A) ADDRESSEE: Davieβ Collison Cave, Patent Attorneys (B) STREET: 1, Little Collins Street (C) CITY: Melbourne (D) STATE: Victoria (E) COUNTRY: AUSTRALIA (F) ZIP: 3000 (v) COMPUTER READABLE FORM: (A) MEDIUM TYPE: Floppy disk (B) COMPUTER: IBM PC compatible (C) OPERATING SYSTEM: PC-DOS/MS-DOS (D) SOFTWARE: PatentIn Release #1.0, Version #1.25 (vi) CURRENT APPLICATION DATA: (A) APPLICATION NUMBER: PCT INTERNATIONAL (B) FILING DATE: 06-MAR-1996 (C) CLASSIFICATION: (vii) PRIOR APPLICATION DATA: (A) APPLICATION NUMBER: AU PN15 2 95 (B) FILING DATE: 06-MAR-199S (viii) ATTORNEY/AGENT INFORMATION: (A) NAME: Hughes h, E j (ix) TELECOMMUNICATION INFORMATION: (A) TELEPHONE: 61-3-9254 2777 (B) TELEFAX: 61-3-9254 2770 (2) INFORMATION FOR SEQ ID Nθ:l: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 1079 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: cDNA (vi) ORIGINAL SOURCE: (A) ORGANISM: Chicken (Callus sp . ) (G) CELL TYPE: T-cell (H) CELL LINE: CCΘ.lh (vii) IMMEDIATE SOURCE: (A) LIBRARY: CCβ.lh (B) CLONE: ChiFN- amma (ix) FEATURE: (A) NAME/KEY: CDS (B) LOCATION: 134..625 (ix) FEATURE: (A) NAME/KEY: mat_peptide (B) LOCATION: 191..625 (ix) FEATURE: (A) NAME/KEY: S'UTR (B) LOCATION: 1..133 (ix) FEATURE: (A) NAME/KEY: 3'UTR (B) LOCATION: 626..1079 (xi) SEQUENCE DESCRIPTION: SEQ ID Nθ:l: GGATCCACTA GTAACGGCCG CCAGTGTGGT GGAATTCAGA AGACATAACT ATTAGAAGCT 60 GAAGCTCACT GAGCTTATAT CTGACATCTC CCAGAAGCTA TCTGAGCATT TGAACTGAGC 120 CATCACCAAG AAG ATG ACT TGC CAG ACT TAC AAC TTG TTT GTT CTG TCT 169 Met Thr Cys Gin Thr Tyr Asn Leu Phe Val Leu Ser - 19 - 15 - 10 GTC ATC ATG ATT TAT TAT GGA CAT ACT GCA AGT AGT CTA AAT CTT GTT 217 Val He Met He Tyr Tyr Gly His Thr Ala Ser Ser Leu Asn Leu Val - 5 1 5 CAA CTT CAA GAT GAT ATA GAC AAA CTG AAA GCT GAC TTT AAC TCA AGT 265 Gin Leu Gin Asp Asp He Asp Lys Leu Lys Ala Asp Phe Asn Ser Ser 10 15 20 25 CAT TCA GAT GTA GCT GAC GGT GGA CCT ATT ATT GTA GAG AAA CTG AAG 313 His Ser Asp Val Ala Asp Gly Gly Pro He He Val Glu Lys Leu Lys 30 35 40 AAC TGG ACA GAG AGA AAT GAG AAA AGG ATC ATA CTG AGC CAG ATT GTT 361 Asn Trp Thr Glu Arg Asn Glu Lys Arg He He Leu Ser Gin He Val 45 50 55 TCG ATG TAC TTG GAA ATG CTT GAA AAC ACT GAC AAG TCA AAG CCG CAC 409 Ser Met Tyr Leu Glu Met Leu Glu Asn Thr Asp Lys Ser Lys Pro His 60 65 70 ATC AAA CAC ATA TCT GAG GAG CTC TAT ACT CTG AAA AAC AAC CTT CCT 457 He Lys His He Ser Glu Glu Leu Tyr Thr Leu Lys Asn Asn Leu Pro 75 80 85 GAT GGC GTG AAG AAG GTG AAA GAT ATC ATG GAC CTG GCC AAG CTC CCG 505 Asp Gly Val Lys Lys Val Lys Asp He Met Asp Leu Ala Lys Leu Pro 90 95 100 105 ATG AAC GAC TTG AGA ATC CAG CGC AAA GCC GCG AAT GAA CTC TTC AGC 553 Met Asn Asp Leu Arg He Gin Arg Lys Ala Ala Asn Glu Leu Phe Ser 110 115 120 ATC TTA CAG AAG CTG GTG GAT CCT CCG AGT TTC AAA AGG AAA AGG AGC 601 He Leu Gin Lys Leu Val Asp Pro Pro Ser Phe Lys Arg Lys Arg Ser 125 130 135 CAG TCT CAG AGG AGA TGC AAT TGC TAATGGCATC TTATGACCTt CTGTGCTCAA 655 Gin Ser Gin Arg Arg Cys Asn Cys 140 145 CTATTTTAAA TTTTACAATG CACAATTTTT ATGTTGTGAT TTTTTAACTG AGTTTATATA 715 CATTTATTTA TTAATATTTA AGTATTTTAA ATAATTATTT ATATTAAAAA AAAACCAGGC 775 AAACAATGAA AGTATTTATA CCTCCTACTG CTGTGTAAGA J.ACGGATTGT GGTCTTAAAA 835 TACTGTCTAT CTGTTGTGTG TGGGTTGACT GAAAATACCG AATGAGGTGG ATGTTTACCA 895 GTTTCTGTGT GGGAAATACT GAATTGGAGG TGGATCTGTA CTCAAGAAAA CCCACTCATC 955 CCGGTCAGTC TAGTATTTCT AAATCCAAAT CAAGGAGTGG CTTGTTTAAA GGGAAAAAAT 1015 GTGAGCACTC TCTGACTGGG TCTTAGAGAT TTTACTGATG GTTTGGCATG ACTAAGAATT 1075 TAGG 1079 (2) INFORMATION FOR SEQ ID NO:2: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 164 amino acids (B) TYPE: amino acid (D) TOPOLOGY: linear (ii) MOLECULE TYPE: protein (xi) SEQUENCE DESCRIPTION: SEQ ID Nθ:2: Met Thr Cys Gin Thr Tyr Asn Leu Phe Val Leu Ser Val He Met He -19 -15 -10 -5 Tyr Tyr Gly His Thr Ala Ser Ser Leu Asn Leu Val Gin Leu Gin Asp 1 5 10 Asp He Asp Lys Leu Lys Ala Asp Phe Asn Ser Ser His Ser Asp Val 15 20 25 Ala Asp Gly Gly Pro He He Val Glu Lys Leu Lys Asn Trp Thr Glu 30 35 40 45 Arg Asn Glu Lys Arg He He Leu Ser Gin He Val Ser Met Tyr Leu 50 55 60 Glu Met Leu Glu Asn Thr Asp Lys Ser Lys Pro His He Lys His He 65 70 75 Ser Glu Glu Leu Tyr Thr Leu Lys Asn Asn Leu Pro Asp Gly Val Lys 80 85 90 Lys Val Lys Asp He Met Asp Leu Ala Lys Leu Pro Met Asn Asp Leu 95 100 105 Arg He Gin Arg Lys Ala Ala Asn Glu Leu Phe Ser He Leu Gin Lys 110 115 120 125 Leu Val Asp Pro Pro Ser Phe Lys Arg Lys Arg Ser Gin Ser Gin Arg 130 135 140 Arg Cys Asn Cys 145

Claims: THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. An isolated nucleic acid molecule which encodes or is complementary to a nucleic acid molecule which encodes, an avian cytokine polypeptide or a f nctional or immunologicaily-interactive homologue, analogue or derivative thereof, wherein said polypeptide is a Type II interferon or a Type II interferon-like molecule. 2. An isolated nucleic acid molecule according to claim 1, wherein said Type II interferon is IFN-γ. 3. An isolated nucleic acid molecule according to claim 2, wherein said IFN-γ is derived from a species of poultry selected from the list comprising chickens, ducks, geese, turkeys, bantams, quails or guinea fowl, amongst others. 4. An isolated nucleic acid molecule according to claim 3, wherein said IFN-γ is the ChlFN-γ. 5. An isolated nucleic acid molecule according to claim 4, further comprising a sequence of nucleotides substantially as set forth in SEQ ID NO:l or a homologue, analogue or derivative thereof including any single or multiple nucleotide substitutions, deletions and/or additions thereto. 6. An isolated nucleic acid molecule comprising a sequence of nucleotides corresponding or complementary to the sequence of nucleotides set forth in SEQ ID NO:l, or at least 40% identical thereto. 7. An isolated nucleic acid molecule according to claim 6, wherein said nucleic acid molecule further encodes or is complementary to a nucleic acid molecule which encodes an avian cytokine polypeptide or a functional or immunologically- interactive homologue, analogue or derivative thereof, wherein said avian cytokine polypeptide is a Type II interferon or a Type II interferon-like molecule. 8. An isolated nucleic acid molecule according to claim 7, wherein said Type II interferon is IFN-γ. 9. An isolated nucleic acid molecule which encodes or is complementary to a nucleic acid molecule which encodes, an avian Type II interferon or Type II interferon- like molecule, wherein said nucleic acid molecule is capable of hybridising under at least low stringency conditions to the nucleic acid molecule set forth in SEQ ID NO:l or a complementary strand thereof. 10. An isolated nucleic acid molecule according to claim 9, further comprising a sequence of nucleotides which is at least 40% identical to the nucleotide sequence set forth in SEQ ID NO: 1. 11. An isolated nucleic acid molecule according to claim 9 or 10 wherein said Type II interferon is IFN-γ. 12. An isolated nucleic acid molecule according to claim 11 wherein said IFN-γ is a ChlFN-γ molecule. 13. A method of identifying an avian Type II interferon genetic sequence or Type II interferon-like genetic sequence or a homologue, analogue or derivative thereof, said method comprising contacting genomic DNA, mRNA or cDNA with a hybridisation- effective amount of a probe comprising at least 50 nucleotides in length isolated from the nucleotide sequence set forth in SEQ ID NO:l and then detecting said hybridisation. 14. A method according to claim 13, wherein said avian Type II interferon genetic sequence originates from an avian species selected from the list comprising chickens, turkeys, bantams, quails, guinea fowl, ducks, geese, ostriches, emus, pigeons, canaries, budgerigars, parrots and finches, amongst others. 15. A method according to claim 14, wherein said probe is labelled with a reporter molecule. 16. A method according to claim 15, wherein the reporter molecule is a radioisotope or a biotinylated molecule. 17. A method of identifying an avian Type II interferon genetic sequence or Type II interferon-like genetic sequence or a homologue, analogue or derivative thereof, said method comprising contacting two non-complementary nucleic acid primer molecules of at least 12 nucleotides in length derived from the nucleotide sequence of an avian Type II interferon gene with a nucleic acid template molecule to which said primers are capable of hybridising and amplifying specific nucleic acid molecule copies of the template molecule in a polymerase chain reaction. 18. A method according to claim 17, wherein said primer molecules are derived from an avian Type II interferon gene which is an IFN-γ gene. 19. A method according to claim 18 wherein said IFN-γ gene is ChlFN-γ. 20. A method according to claim 19 wherein said ChlFN-γ gene comprises a sequence of nucleotides set forth in SEQ ID NO:l or a homologue, analogue or derivative thereof. 21. A method according to claim 20, wherein one of said primer molecules comprise a sequence of nucleotides substantially the same as the sequence of the sense primer set forth in Example 8. 22. A method according to claim 20, wherein one of said primer molecules comprise a sequence of nucleotides substantially the same as the sequence of the antisense primer set forth in Example 8. 23. A genetic construct including but not limited to z viral vector or plasmid molecule for expression of an avian cytokine in a prokaryotic or eukaryotic cell, said genetic construct comprising a nucleic acid molecule which encodes an avian cytokine polypeptide or a homologue, analogue or derivative thereof operably linked to a promoter sequence, wherein said polypeptide is a Type II interferon or Type II interferon-like molecule. 24. A genetic construct according to claim 23 wherein said Type II interferon is IFN- γ. 25. A genetic construct according to claim 24 wherein said IFN-γ is ChlFN-γ. 26. A genetic construct according to claim 25 wherein said ChlFN-γ comprises a sequence of amino acids substantially as set forth in SEQ ID NO:2, or is at least 40% identical thereto. 27. A genetic construct according to any one of claims 23 to 26 suitable for expression in a prokaryotic cell including but not limited to bacteria. 28. A genetic construct according to claim 27 designated pQE ChlFN-γ. 29. A genetic construct according to any one of claims 23 to 26 suitable for expression in a eukaryotic such as yeast cell or mammalian cell cell selected from the list comprising COS, VERO, HeLa, mouse C127, Chinese hamster ovary (CHO), WI-38, baby hamster kidney (BHK) or MDCK cells, amongst others. 30. A genetic construct according to claim 29 designated pcDNA3/avian G-IFN. 31. A genetic construct comprising a nucleic acid molecule which encodes or is complementary to a nucleic acid molecule which encodes an avian cytokine polypeptide or a homologue, analogue or derivative thereof, wherein said polypeptide is a fusion polypeptide between a first Type II interferon or Type II interferon-like molecule and a second Type II interferon or a Type I interferon selected from the list comprising IFN- α, IFN-β, Ch IFN-α or Ch IFN-β, amongst others. 32. A genetic construct according to claim 31, wherein said first Type II interferon is IFN-γ. 33. A genetic construct according to claim 32 wherein said IFN-γ is a ChlFN-γ molecule. 34. A genetic construct according to claim 33, wherein said ChlFN-γ comprises a sequence of amino acid residues substantially as set forth in SEQ ID NO:2 or is at least 40% identical thereto. 35. A recombinant avian cytokine polypeptide or a functional or immunologically- interactive homologue, analogue or derivative thereof, wherein said cytokine is a Type II interferon or interferon-like molecule. 36. A recombinant avian cytokine according to claim 35 wherein said Type II interferon or interferon-like molecule is IFN-γ. 37. A recombinant avian cytokine according to claim 36 wherein said IFN-γ is ChlFN-γ. 38. A recombinant avian cytokine according to claim 37 wherein said ChlFN-γ molecule comprises a sequence of amino acids which is substantially the same as the amino acid sequence set forth in SEQ ID NO:2 or is at least 40% identical to all or a part thereof. 39. A method of producing a recombinant avian cytokine in a cell comprising expressing in said cell a nucleic acid molecule according to any one of claims 1 to 12. 40. A method of producing a recombinant avian Type II interferon or Type II interferon-like molecule in a cell comprising the steps of: (i) introducing into said cell a genetic construct according to any one of claims 23 to 34; and (ii) culturing said cell for a time and under conditions sufficient for said nucleic acid molecule to be expressed. 41. A method of producing a recombinant avian Type II interferon or Type II interferon-like molecule in a cell according to claim 40, wherein said method further comprises the step of isolating said Type II interferon or Type II interferon-like molecule from said cell. 42. A method of producing a recombinant avian cytokine in a cell comprising the steps of: (i) introducing into said cell a genetic construct comprising a nucleic acid molecule which encodes or is complementary to a nucleic acid molecule which encodes an avian cytokine polypeptide or a homologue, analogue or derivative thereof, wherein said polypeptide is a fusion polypeptide between a first Type II interferon or Type II interferon-like molecule and a second Type II interferon or a Type I interferon selected from the list comprising IFN-α, IFN-β, Ch IFN-α or Ch IFN-β, amongst others or any other cytokine or cytokine-like molecule; and (ii) culturing said cell for a time and under conditions sufficient for said nucleic acid molecule to be expressed. 43. A method of producing a recombinant avian cytokine in a cell according to claim 42, wherein said first Type II interferon and said second Type II interferon have different amino acid sequences. 44. A method of producing a recombinant avian cytokine in a cell according to claim 43, wherein said first Type II interferon is IFN-γ 45. A method of producing a recombinant avian cytokine in a cell according to claim 44, wherein said IFN-γ is ChlFN-γ. 46. A method of producing a recombinant avian cytokme in a cell according to claim 45, wherein said ChlFN-γ comprises a sequence of amino acid residues substantially as set forth in SEQ ID NO:2 or is at least 40% identical thereto. 47. An isolated cell which expresses an avian cytokine, wherein said cytokine is a Type II interferon or Type II interferon-like molecule. 48. An isolated cell according to claim 47, wherein said Type II interferon is IFN-γ. 49. An isolated cell according to claim 48, wherein said IFN-γ is ChlFN-γ. 50. An isolated cell according to claim 49, wherein said ChlFN-γ comprises a sequence of amino acids substantially as set forth in SEQ ID NO:2, or is at least 40% identical thereto. 51. An isolated cell according to any one of claims 47 to 50, wherein said cell is a eukaryotic cell. 52. An isolated cell according to claim 51, wherein said eukaryotic cell is an avian cell. 53. An isolated cell according to claim 52, wherein said avian cell is a T cell. 54. An isolated cell according to claim 53, wherein said T cell is the CC8. lh cell line (AGAL Accession No. N94/46035). 55. An isolated cell according to claim 51, wherein the avian cytokine is a recombinant molecule and said eukaryotic ceil is a mammalian, yeast, insect or plant cell or a cell line selected from the list comprising COS, VERO, HeLa, mouse C127, Chinese hamster ovary (CHO), WI-38, baby hamster kidney (BHK) or MDCK cells, amongst others. 56. An isolated cell according to claim 55, wherein said cell is the COS cell line containing the pCDNA3/avian G-IFN plasmid (AGAL Accession No. N95/12388). 57. An isolated cell according to any one of claims 47 to 50, wherein said cell is a prokaryotic cell and the cytokine is a recombinant molecule. 58. An isolated cell according to claim 57, wherein said cell is a bacterium. 59. An isolated cell according to claim 58, wherein said bacerium is Escherichia coli. 60. An isolated cell according to claim 59, wherein said Escherichia coli cell is E.coli strain pQE ChlFN-γ (AGAL Accession No. N96/9464). 61. An isolated cell which expresses a nucleic acid molecule which encodes or is complementary to a nucleic acid molecule which encodes an avian cytokine polypeptide or a homologue, analogue or derivative thereof, wherein said polypeptide is a fusion polypeptide between a first Type II interferon or Type II interferon-like molecule and a second Type II interferon or a Type I interferon selected from the list comprising IFN- α, IFN-β, Ch IFN-α or Ch IFN-β, amongst others. 62. An isolated cell according to claim 61, wherein said first Type II interferon is IFN-γ. 63. An isolated cell according to claim 62, wherein said IFN-γ is ChlFN-γ. 64. An isolated cell according to claim 63, wherein said ChlFN-γ comprises a sequence of amino acids substantially as set forth in SEQ ID NO:2 or is at least 40% identical thereto. 65. An isolated cell comprising a genetic construct according to any one of claims 23 to 34. 66. A method of treatment or prophylaxis of an avian animal exposed to or infected with a pathogenic organism, said method comprising administering to said avian animal an immunoresponsive effective amount of an avian cytokine or a derivative thereof for a time and under conditions sufficient to maintain, stimulate or enhance the irnmmunoresponsiveness of said animal. 67. A method of treatment or prophylaxis of an avian animal according to claim 66, wherein said avian cytokine is a Type II interferon or Type II interferon-like molecule or a fusion polypeptide between a first Type II interferon and either a second Type II interferon or Type I interferon selected from the list comprising IFN-α, IFN-β, ChlFN-α or ChlFN-β. 68. A method of treatment or prophylaxis of an avian animal according to claim 67, wherein said Type T I interferon, and said first Type II interferon but not said second Type II interferon, is IFN-γ. 69. A method of treatment or prophylaxis of an avian animal according to claim 68, wherein said IFN-γ is ChlFN-γ. 70. A method of treatment or prophylaxis of an avian animal according to claim 69, wherein said ChlFN-γ comprises a sequence of amino acids substantially the same as the amino acid sequence set forth in SEQ ID NO:2, or is at least 40% identical thereto. 71. A method of treatment or prophylaxis of an avian animal according to any one of claims 66 to 70, wherein said avian animal is a species of poultry, a domestic bird or a game bird selected from the list comprising chickens, turkeys, bantams, quails, guinea fowl, ducks, geese, ostriches, emus, pigeons, canaries, budgerigars, parrots and finches, amongst others. 72. A method of treatment or prophylaxis of an avian animal according to any one of claims 66 to 71, wherein said pathogenic organism is a viral infectious agent. 73. A method of treatment or prophylaxis of an avian animal according to claim 72, wherein said viral infectious agent is selected from the list comprising infectious bronchitis virus, avian infectious laryngeotracheitis virus, infectious bronchitis virus, Newcastle disease virus, Marek's Disease virus, chicken anemia virus and avian influenza virus, amongst others. 74. A method of treatment or prophylaxis of an avian animal according to any one of claims 66 to 71, wherein said pathogenic organism is a prokaryote selected from Exoli, Salmonella ssp., Eimeria ssp. or Mycoplasma ssp. amongst others. 75. A method of treatment or prophylaxis of an avian animal according to any one of claims 66 to 71, wherein said avian cytokine is administered by injection in ovo or post-hatching. 76. A method of treatment or prophylaxis of an avian animal according to claim 75, wherein said injection is by an intra-peritoneal, intra-dermal, intra-muscular, intra-ocular, intra- venous or sub-cutaneous route. 77. A method of treatment or prophylaxis of an avian animal according to any one of claims 66 to 71, wherein said avian cytokine is administered by ingestion. 78. A method of treatment or prophylaxis of an avian animal according to claim 77, wherein said avian cytokine is administered further as a medicated foodstuff or therapeutic foodstuff. 79. A method of treatment or prophylaxis of an avian animal according to any one of claims 66 to 71, wherein said avian cytokine is administered by genetic means. 80. A method of treatment or prophylaxis of an avian animal according to claim 79, wherein said genetic means comprises administering to said avian an isolated nucleic id molecule which encodes or is complementary to an isolated nucleic acid molecule which encodes said cytokine and is capable of being expressed therein. 81. A method of treatment or prophylaxis of an avian animal exposed to or infected with a pathogenic organism according to claim 79 wherein said genetic means comprises administering an attenuated live viral vector or attenuated live bacterial vector or non-replicating viral vector or plasmid molecule comprising a genetic construct capable of expressing said cytokine in said avian animal. 82. An adjuvant comprising an avian cytokine molecule, wherein said cytokine is a Type II interferon or interferon-like molecule or a fusion molecule between said Type II interferon molecule and a second cytokine molecule and optionally, a pharmaceutically-acceptable carrier, excipient or diluent. 83. An adjuvant according to claim 82, wherein said Type II interferon is IFN-γ. 84. An adjuvant according to claim 83, wherein said IFN-γ is ChlFN-γ. 85. An adjuvant according to claim 84, wherein said ChlFN-γ comprises a sequence of amino acids substantially as set forth in SEQ ID NO:2, or is at least 40% identical thereto. 86. An adjuvant according to claim 82, wherein said second cytokine molecule is a Type I interferon including IFN-α, IFN-β, ChlFN-α or ChlFN-γ or any Type II interferon molecule. 87. A vaccine composition for the prophylactic treatment of an avian species comprising an adjuvant according to any one of claims 82 to 86 in combination with an antigen such as a live infectious organism, a killed organism, recombinant vaccine or a recombinant subunit vaccine derived therefrom and optionally, one or more pharmaceutically acceptable carriers or diluents acceptable for veterinary use. 88. A vaccine composition according to claim 87, wheiein said antigen is derived from a viral or bacterial or other pathogen selected from the list comprising infectious bursal disease virus, avian infectious bronchitis virus, avian infectious laryngeotracheitis virus, infectious bronchitis virus, Newcastle disease virus, Marek's Disease virus, chicken anemia virus, avian influenza virus, E.coli, Salmonella ssp. or Eimeria ssp, amongst others. 89. A method of enhancing and/or stimulating an immune response to one or more antigens in an avian animal, said method comprising administering to said animal an immunomodulatingly effective amount of an avian cytokine. 90. A method according to claim 89, wherein said avian cytokine is a Type II interferon or interferon-like molecule or a fusion molecule between said Type II interferon molecule and a second cytokine molecule and optionally, a pharmaceutically- acceptable carrier, excipient or diluent. 91. A method according to claim 90, wherein said Type II interferon is IFN-γ. 92. A method according to claim 91, wherein said IFN-γ is ChlFN-γ. 93. A method according to claim 92, wherein said ChlFN-γ comprises a sequence of amino acids substantially as set forth in SEQ ID NO:2, or is at least 40% identical thereto. 94. A method according to any one of claims 89 to 93, wherein said avian animal is a species of poultry, a domestic bird or a game bird selected from the list comprising chickens, turkeys, bantams, quails, guinea fowl, ducks, geese, ostriches, emus, pigeons, canaries, budgerigars, parrots and finches, amongst others. 95. A method according to any one of claims 89 to 94, wherein said avian cytokine is administered by injection, ingestion, aerosol or genetic means as hereinbefore defmed, either in ovo or post-hatching. 96. A veterinary pharmaceutical composition for use in the treatment of poultry, domestic birds or game birds to enhance the immune system, accelerate maturation, improve immunocompetence or facilitate immunomodulation, wherein said pharmaceutical composition comprises a recombinant avian Type II interferon or interferon-like molecule or a fusion molecule between a Type II interferon and a second cytokine and one or more pharmaceutically acceptable carriers and or diluents suitable for veterinary use. 97. A veterinary composition according to claim 96, further comprising a second cytokine molecule which is capable of acting in synergy with said recombinant Type II interferon or said fusion molecule. 98. A veterinary composition according to claims 96 or 97, wherein said second cytokine is IFN-α, IFN-β, ChlFN-α, ChlFN-β or a Type II interferon different from said Type II interferon molecule. 99. A veterinary composition according to any one of claims 96 to 98, wherein said Type II interferon is IFN-γ. 100. A veterinary composition according to claim 99, wherein IFN-γ is ChlFN-γ. 101. A veterinary composition according to claim 100, wherein said ChlFN-γ comprises a sequence of amino acids substantially the same as the amino acid sequence set forth in SEQ ID NO:2, or is at least 40% identical thereto. 102. A method of enhancing the growth performance of an avian species comprising administering thereto an avian Type II interferon or interferon-like molecule or a fusion polypeptide between an avian Type II interferon and a second cytokine molecule. 103. A method according to claim 102, wherein said second cytokine is IFN-α, IFN-β, ChlFN-α, ChlFN-β or any Type II interferon molecule. 104. A method according to claim 102 or claim 103, wherein said Type II interferon or interferon-like molecule is IFN-γ. 105. A method according to claim 104, wherein said IFN-γ is ChlFN-γ. 106. A method according to claim 105, wherein said ChlFN-γ comprises a sequence of amino acids substantially the same as the aπ-ino acid sequence set forth in SEQ ID NO:2 or is at least 40% identical thereto. 107. A method according to any one of claims 102 to 106, wherein said Type II interferon or fusion molecule is administered by injection, ingestion, aerosol or genetic means as hereinbefore defined. 108. An immunologically- interactive molecule which is capable of binding to an avian Type II interferon or Type II interferon-like molecule or a homologue, analogue or derivative thereof. 109. An immunologically-interactive molecule according to claim 108, wherein said Type II interferon or interferon-like molecule is IFN-γ. 110. An immunologically-interactive molecule according to claim 109, wherein said IFN-γ is ChlFN-γ. 111. An immunologically-interactive molecule according to claim 110, wherein said ChlFN-γ comprises a sequence of amino acids substantially the same as the amino acid sequence set forth in SEQ ID NO:2 or is at least 40% identical thereto. 112. An immunologically-interactive molecule according to any one of claims 108 to 111, further defined as an antibody molecule. 113. A medicated or therapeutic foodstuff comprising a recombinant avian cytokine molecule according to any one of claims 35 to 38 in a form suitable for ingestion by a poultry species, domestic bird or game bird. 114. An immunologically-interactive molecule according to any one of claims 108 to 112 when used to assay the amount of avian Type II interferon or Type II interferon-like molecule, in particular IFN-γ, in a bird species. 115. An immunologically-interactive molecule according to claim 114 wherein said assay is used for the selection of genetic stocks of birds which express or can be induced to express high levels of an avian cytokine, in particular a Type-II interferon or interferon-like molecule such as IFN-γ. 116. An immunologically-interactive molecule according to claim 115, wherein said assay is used for the selection of a selected genetic stock of birds which further exhibits improved disease-resistance. 117. An immunologically-interactive molecule according to claim 116, wherein said disease-resistance is to viral, bacterial or other pathogen selected from the list comprising infectious bursal disease virus, avian infectious bronchitis virus, avian infectious laryngeotracheitis virus, infectious bronchitis virus, Newcastle disease virus, Marek's Disease virus, chicken anemia virus, avian influenza virus, E.coli, Salmonella ssp. or Eimeria ssp., amongst others. 118. An immunologically-interactive molecule according to claim 114, wherein said assay is to determine the magnitude of an immune response in said bird. 119. An immunologically-interactive molecule according to claim 118, wherein said immune response is an immune response to a viral, bacterial or other pathogen selected from the list comprising infectious bursal disease virus, avian infectious bronchitis virus, avian infectious laryngeotracheitis virus, infectious bronchitis virus, Newcastle disease virus, Marek's Disease virus, chicken anemia virus, avian influenza virus, E.coli, Salmonella ssp. or Eimeria ssp., amongst others. 120. An immunologically-interactive molecule according to any one of claims 108 to 112 when used in the purification of an avian Type II interferon or Type II interferon- like molecule. 121. A diagnostic assay for measuring the level of avian Type II interferon or interferon-like molecule in a bird comprising the steps of contacting a biological sample obtained from said bird with an antibody raised against an avian Type II interferon molecule for a time and under conditions sufficient to allow the formation of an antibody-cytokine complex and then detecting said complex formation. 122. A diagnostic assay according to claim 121, wherein said assay is an immunoassay. 123. A diagnostic assay according to claim 122, wherein said immunoassay is for the selection of genetic stocks of birds which express high levels of an avian cytokine, in particular a Type II interferon or interferon-like molecule such as IFN-γ. 124. A diagnostic assay according to claim 122, wherein said immunoassay is to determine the presence of or to quantitate the magnitude of an immune response in a bird species. 125. A diagnostic assay according to claim 124, wherein said immune response is to a viral, bacterial or other pathogen selected from the list comprising infectious bursal disease virus, avian infectious bronchitis virus, avian infectious laryngeotracheitis virus, infectious bronchitis virus, Newcastle disease virus, Marek's Disease virus, chicken anemia virus, avian influenza virus, E.coli, Salmonella ssp. or Eimeria ssp., amongst others. 126. A diagnostic assay according to any one of claims 121 to 125, wherein said immunoassay is used to measure the level of cell-mediated immunity following vaccination of a bird with an antigen.

Inventors: DIGBY MATTHEW ROBERT, LOWENTHAL JOHN WILLIAM, O'NEIL TERRI ELLEN, RHODES STEPHEN, YORK JENNIFER JOY, DIGBY, MATTHEW, ROBERT, LOWENTHAL, JOHN, WILLIAM, O'NEIL, TERRI, ELLEN, RHODES, STEPHEN, YORK, JENNIFER, JOY
Applicants: COMMW SCIENT IND RES ORG, DIGBY MATTHEW ROBERT, LOWENTHAL JOHN WILLIAM, NEIL TERRI ELLEN O, RHODES STEPHEN, YORK JENNIFER JOY, COMMONWEALTH SCIENTIFIC AND INDUSTRIAL RESEARCH OR, DIGBY, MATTHEW, ROBERT, LOWENTHAL, JOHN, WILLIAM, O'NEIL, TERRI, ELLEN, RHODES, STEPHEN, YORK, JENNIFER, JOY
Application year: 1996
Main classification: C12N15
IPC codes: A61K38, A61K39, C07K14, C07K16, C12N15