EQUINE HERPESVIRUS GLYCOPROTEINS

Abstract: Disclosed are serological assays based on unique sequence type-specifice gG proteins and polypeptides capable of distinguishing the closely related EHV4 and EHV1 viruses. The assays are capable of clearly and unambiguously distinguishing animals infected with EHV4 or EHV1 and thereby distinguishing the EHV4 infection: equine rhinopheumonitis, causing "snotty noses" from the more dramatic consequences of EHV1 infection; equine abortion, which often results in an "abortion storm" and high loss of livestock. Further disclosed are the unique type-specific epitopes of EHV4 and EHV1, recombinantly derived novel nucleic acid sequences and proteins which are useful in providing assay reagents, antibodies, vaccines, probes and associated peripherals for diagnosis and control.

Description: TITLE EQUINE HERPESVIRUS GLYCOPROTEINS INTRODUCTION TO INVENTION This invention relates to Equine Heφesvirus and in particular to type-specific glycoproteins thereof and diagnostic tests and clinical applications associated with the characterization of such glycoproteins. BACKGROUND OF INVENTION Equine rhinopheumonitis and equine abortion are commonly recognised diseases of horses caused by two distinct but antigenically related viruses that are designated equine heφesvirus 4 and equine heφesvirus 1, known as EHV4 and EHVl respectively. Because the viruses are related antigenically it has not been possible to date by serological examination (blood test), to determine whether a horse has been infected with either or both EHV4 or EHVl. For example, if a horse had been infected with EHV4 as a foal it would develop antibodies in its serum that would react with not only EHV4 but with EHVl as well, so one would not know that such a foal had been infected with only EHV4. However, since 1981 it has been repeatedly shown that the restriction endonuclease fingeφrints of the two viruses are distinctly different with respiratory isolates and fetal isolates almost invariably typing as EHV4 and EHVl respectively. The availability of specific monoclonal antibodies (MAbs) directed to either EHV4 or EHVl has also allowed consistent and specific typing of isolates of the two viruses. The major significance in developing a specific antibody test relates to the fact that both these heφesviruses are believed, after primary infection, to establish a persistent, latent and life-long infection. Either virus may from time to time be reactivated from the latent state (just as is the case with recurrent cold sores in humans infected with heφes simplex virus); the virus, reactivated from the latent state, will usually cause recurrent disease in the host horse but more importantly such a horse will either directly or indirectly by contact act as a source of infection for other horses. In this way, for EHV4, there is usually in the annual foal crop born on a farm an annual round of respiratory disease ("snotty" noses). Such an occurrence is almost an accepted part of breeding horses. Occasionally foals become severely affected and require treatment or die because of severe secondary complications such as bacterial pneumonia. While the natural history of EHVl is less clearly understood, there is an assumption that the virus does establish persistent, lifelong latent, infections. Upon reactivation there may be a further bout of respiratory disease. However, a far more serious consequence for other horses infected by contact with the first horse (index case) occurs on breeding farms when a pregnant mare in a paddock reactivates the virus and transmits it to other in-contact pregnant mares. The index case mare may herself abort or cause abortion in one or more in contact mares. An aborted foetus and the foetal membranes and fluids are heavily infected with EHVl and contaminate the site where abortion occurs. Other mares in the paddock, being naturally curious, come to the site of abortion and sniff the foetus and membranes. In this way, often close to 100% of the mares in the paddock become infected and abort within 10 or 20 days causing what is commonly known as an "abortion storm". Such outbreaks of EHVl abortion are of considerable economic importance to the equine, particularly thoroughbred and standardbred, industries worldwide. There is a need for accurate, type-specific serological surveillance of horses for the presence of EHV4 and/or EHVl antibodies to assist in our understanding of the epidemiology of these viruses, particularly EHVl. Presently, however, EHVl or EHV4 antibodies in polyclonal serum cannot be differentiated because of the extensive antigenic cross-reactivity between the two viruses. The availability of such a specific serological test would also have profound implications in the control, perhaps eradication, of EHVl and in the selection of candidate horses for vaccination. The antibody responses of the horse to these viruses is largely directed to the envelope glycoproteins. EHVl homologues to nine of the ten recognized heφes simplex virus 1 (HSN1) glycoproteins have been identified from DΝA sequence analyses; gB, gC, gD, gE, gG, gH, gl, gK, and gL. The remaining HSN1 glycoprotein- gJ, has a positional counteφart in the US region of EHN1, gene 71, although these two genes do not show any significant homology. Also, EHVl possesses at least three other glycoproteins designated gp2, gplO, which are the homologues of the HSN1 tegument proteins NP13/14 and gp21/22a. In the case of EHN4, which unlike EHN1 has only been partially sequenced, glycoprotein genes encoding gB, gC, gG and gH homologues have been identified which show amino acid identities of 89%, 79%, 58% and 85% respectively with their EHVl counteφarts. Homologous EHN4 and EHVl genes map to collinear positions in their respective genomes. EHVl glycoproteins gp2, gplO, gC (gpl3), gB (gpl4), gD (gpl8) and gp21/22a have been definitively identified by SDS-PAGE as have EHN4 glycoproteins gp2, gplO, gC (gpl3), gB (gpl4), gD (gpl8) and gG. Using combinations of EHN1 EHN4 MAbs and polyclonal post-EHNl only or post-EHV4 only horse sera it has been shown that each of the glycoproteins possesses both type-common and type-specific epitopes The two exceptions are gp21 22a which has been relatively poorly studied and EHN4 gG which appears to elicit a type-specific serological response. To date, glycoprotein G (gG) homologues of other heφesviruses have been used as a basis for diagnostic testing and clinical application. In particular, gG (alternatively called gX) of pseudorabies virus (PRN) has been used in the development of gG deletion mutant vaccines linked to a diagnostic test for PRV of pigs. Also gG of human heφes simplex viruses (HSV) 1 and 2 are different enough to allow tests such as ELISA to be developed for the detection of antibodies to either HSV1 or 2 in the serum of humans. However, in spite of these data for PRV and HSN 1 and 2 it could not have been predicted that the same glycoprotein, namely glycoprotein G of EHV4 and EHVl, would serve a role in diagnosis and vaccine development. For PRN, only a single virus is involved, so the question of distinguishing between two viruses is not relevant. For HSN 1 and 2, while two viruses are involved, the gG proteins are different in very different ways from EHV4 and EHVl gGs. In particular, the molecular sizes of unglycosylated HSN1 and HSN2 gGs differ greatly with HSN1 at 26K and, HSV2 at 77K, whereas the sizes of unglycosylated EHN4 and EHN1 gG differ only slightly at 44K and 45K respectively. It is reasoned that the type-specificity of the entire HSN1 and 2 gG proteins resulted from a major deletion in the case of the HSN1 gG gene whereby some 1383 nucleotides have been "lost" from a total gene (in the case of HSN2) of 2097 nucleotides. The loss of more than half the coding sequence of HSN1 gG results in a non glycosylated protein of only 26K vs 77K for HSN2 gG. While it is recognised that a positive ELISA is required for the differentiation of humans infected with either HSV1 or 2 it could have been reasoned that if the two genes were of approximately the same size then the two gGs would be cross-reactive. For EHN4 and EHN1 it is shown that while the two gGs are approximately the same size they are still type-specific. This could not have been predicted from prior art (HSN) material or from sequence data alone. On the later point the fact that EHN4 and EHN1 gG are 58% similar at the amino acid level it could in fact have been predicted that cross-reactive epitopes would almost certainly have existed and hence gG could not have been used in the concurrently described invention to differentiate the two equine viruses. The findings of the current invention are based on the analysis of a specifically selected set of horse serums for which the previous infection/vaccination history of particular horses was known * Detailed analysis of these serums show that cross-reactive epitopes are either not present or are not important in eliciting an antibody response in the natural host. Such a highly distinctive property of these epitopes was quite unexpected and has allowed the development of the instant invention. OBJECTAND STATEMENTOFINVENTION One object of this invention is to characterize a protein or protein set or derivatives thereof that are capable of applications in the diagnosis and differentiation of EHV4 and EHVl. A second object of this invention is to provide immunological agents associated with the control of EHN4 and EHVl. A third object of this invention is to provide diagnostic methods, tests, reagents and peripherals associated with the diagnosis and differentiation of EHN4 and EHVl. Accordingly the invention provides, in one broad aspect, envelope glycoproteins of equine heφesvirus capable of distinguishing equine heφesvirus 4 and equine heφesvirus 1. The glycoproteins are preferably type-specific to EHV4 and EHVl invoking minimal or negligible cross-reaction and incoφorating minimal or negligible type-common epitopes between EHN4 and EHNl. The glycoproteins most preferably belong to the glycoprotein set G, known as gG, being EHN4 gG pertaining to EHN4 and EHVl gG pertaining to EHVl. EHV4 gG is secreted into the medium of infected cell cultures. EHN1 gG has not been observed as a secretion into the medium of infected cells. The EHN4 gG glycoprotein preferably comprises a 405 amino acid sequence corresponding to an unglycosylated Λfr value of 44 kilodaltons. The EHN1 gG glycoprotein preferably comprises a 411 amino acid sequence corresponding to an unglycosylated Mr value of 45 kilodaltons. The EHN4 gG is preferably characterized by the following amino acid sequence: MLAVGATLCLLSFLTGATGRLAPDDLCYAEPRKTGPMPRSKPKHQPLLFEAPKVALTA ESKGCQLILLDPPIDMGYRLEDKIΝASIAWFFDFGΝCRMPIAYREYYDCVGΝAIPSPE TCDGYSFTLVKTEGWEFTIVΝMSLLLQPGIYDSGSFIYSALLDMDV TGRVILΝVEΝ DTΝYPCGMTHCLTADGΝIΝVDETTHTTPHPRAVGCFPELIΝFDA EΝVTFEEMGIPDP ΝSFLDDESDYPΝT DCYSWDLYTYPKSLKQAEGPQTLLIGAVGLRILAQAWKFVEΝET YSQHTRTYTRDAKEVDVTQPSPVQADSVLAKKRTSMKΝΝPIYSEGKPHAKPFSTIDSI HTEGMKΝΝPVYSESLMLΝVQHSDSITTGGV HGLQDCDΝQLKTVYICLALIGLAHVP or subsequences thereof capable of eliciting a type-specific response including naturally occurring derivatives, variants, genetically engineered derivatives, glycosylated forms of the proteins or synthetically made derivatives. The EHV4 gG gene is characterized by a coding region comprising the following nucleotide sequence:- ATTTGGGGTGGAGACGGCGTGGGCCGATACTGTATAAAGTTGTACTACTTACCAGCCC AGTCAGTGTGCTGTAGTGCCACCACCTGTAAAGCTGTGATAAGCTGCAGGCATATGTT GGCTGTGGGAGCAACTCTGTGTTTACTGAGTTTCCTAACTGGCGCTACTGGACGGCTA GCTCCTGACGACCTCTGCTATGCAGAACCCCGCAAAACCGGTCCCATGCCCCGCTCAA AACCTAAACACCAACCCCTACTATTTGAAGCCCCAAAGGTTGCTCTTACGGCAGAGTC AAAGGGTTGTCAACTAATATTGTTAGACCCTCCAATAGACATGGGCTATCGCTTAGAG GACAAGATAAACGCTTCCATTGCTTGGTTTTTTGACTTTGGTAATTGTCGAATGCCCA TCGCATACAGAGAGTACTATGATTGCGTTGGCAACGCAATCCCATCTCCAGAAACATG TGATGGTTACTCATTTACACTTGTTAAAACAGAGGGTGTAGTTGAGTTTACCATCGTA AACATGAGCTTACTGTTGCAGCCTGGAATATACGACAGTGGAAGTTTTATATACAGCG CCCTTCTAGATATGGATGTATTGACTGGACGCGTAATTTTGAACGTGGAGAACGACAC TAACTATCCATGCGGAATGACTCACGGCCTCACTGCGGATGGCAACATCAACGTAGAT GAAACCACGCACACAACCCCACATCCACGTGCTGTCGGGTGTTTTCCAGAACTCATTA ACTTCGATGCATGGGAAAACGTTACATTCGAAGAAATGGGGATACCAGACCCAAACTC ATTTCTTGATGATGAGAGTGATTACCCGAATACAATGGACTGTTACTCGTGGGATTTA TACACATATCCCAAAAGCCTGAAGCAGGCAGAGGGGCCCCAAACCTTGTTAATAGGTG CAGTTGGACTCAGAATACTCGCGCAAGCATGGAAGTTTGTTGAAAATGAAACCTACAG CCAGCATACACGTACGTACACACGTGATGCTAAGGAAGTTGATGTTACACAGCCAAGT CCTGTACAGGCTGATTCTGTCCTCGCCAAGAAACGCACATCTATGAAGAATAACCCTA TTTATTCAGAGGGGAAGCCTCATGCTAAACCGTTCAGCACGATAGACAGCATCCACAC GGAAGGGATGAAGAATAACCCTGTTTATTCAGAGAGCCTCATGCTAAACGTCCAGCAC AGTGACAGCATCACCACCGGGGGTGTGTTGCATGGCCTCCAAGACTGCGACAACCAGC TCAAAACTGTGTATATTTGCCTAGCTCTTATTGGACTCGCACATGTGCCATGATAGGA CTAATAGTTTACATTTTTGTGCTAAGGTCAAAAATATCTTCCCACAATTTATCGCGCT CACAAAATGTAAAACATAGAAACTATCATCGACTTGAGTACGTTGCATAATACATGTC AAAATAAAAGTTAAAAATTAAACATTGTTGTCTGTAATAACTGAGTGTGGTTTTAAAA AATACTAAATCGCGGCAATGTT or degeneracy equivalents or subsequences thereof coding for amino acid sequences or epitopes capable of eliciting a type-specific response. The EHVl gG is preferably characterized by the following amino acid sequence:- MLTVLAALSLLSLLTSATGRLAPDELCYAEPRRTGSPPNTQPERPPVIFEPPTIAIKA ESKGCE ILLDPPIDVSYRREDKVNASIAWFFDFGACR PIAYREYYGCIGNAVPSPE TCDAYSFTLIRTEGIVEFTIVNMSLLFQPGIYDSGNFIYSVLLDYHIFTGRVTLEVEK DTNYPCGMIHGLTAYGNINVDETMDNASPHPRAVGCFPEPIDNEAWANVTFTELGIPD PNSFLDDEGDYPNISDCHSWESYTYPNTLRQATGPQTLLVGAVGLRILAQAWKFVGDE TYDTIRAEAKNLETHVPSSAAESSLENQSTQEESNSPEVAHLRSVNSDDSTHTGGASN GIQDCDSQLKTVYACLALIGLGTCAMIGLIVYICVLRSKLSSRNFSRAQNVKHR YQR EYVA or subsequences thereof capable of eliciting a type-specific response including naturally occurring derivatives, variants, genetically engineered derivatives, glycosylated forms of the proteins or synthetically made derivatives. Preferably the epitopes responsible for eliciting the type-specific response are encompassed by EHV4 gG amino acids 287-382 and EHVl gG amino acids 288-350 (as herein defined). Most preferably the EHV4 epitope is characterized by the following amino acid sequence: ENETYSQHTRTYTRDAKEVDVTQPSPVQADSVLAKKRTSMKNNPIYSEGKPHAKPFST IDSIHTEGMKNNPVYSESLMLNVQHSDSITTGGVLHGL or subsequences thereof capable of eliciting a type-specific response including naturally occurring derivatives, variants, genetically engineered derivatives, glycosylated forms of the proteins or synthetically made derivatives. An alternative EHV4 epitope is characterized by the following amino acid sequence KTGPMPRSKPKHQPLLFEAPKVALT or subsequences thereof capable of elicitmg a type-specific response including naturally occurring derivatives, variants, genetically engineered derivatives, glycosylated forms of the proteins or synthetically made derivatives. The invention further provides EHV4 discontinuous epitopes characterized by a discontinuous combination of the above detailed epitopes or derivatives of these 2 regions, either alone or together, with other regions of the EHV4 gG molecule. The invention further provides plasmid vector pEG4var (as herein defined). Most preferably the EHVl epitope is characterized by the following amino acid sequence GDETYDTIRAEAKNLETHVPSSAAESSLENQSTQEESNSPEVAHLRSVNSDDSTHTGG ASNGI or subsequences thereof capable of eliciting a type-specific response including naturally occurring derivatives, variants, genetically engineered derivatives, glycosylated forms of the proteins or synthetically made derivatives. An alternative EHVl epitope is characterized by the following amino acid sequence. RTGSPPNTQPERPPVIFEPPTIAIK or subsequences thereof capable of eliciting a type-specific response including naturally occurring derivatives, variants, genetically engineered derivatives, glycosylated forms of the proteins or synthetically made derivatives. The invention further provides EHVl discontinuous epitopes characterized by a discontinuous combination of the above detailed epitopes or derivatives of these 2 regions, either alone or together, with other regions of the EHVl gG molecule. The invention further provides a plasmid vector pEGlvar (as herein defined). The invention further provides vaccines for the immunization of horses against EHV4 and/or EHVl. Among the various vaccine types possible are deletion mutant vaccines characterized by the deletion of EHV4 gG amino acids 287-382 and/or deletion of EHVl gG amino acids 288-350 or subsequences thereof or amino acids located elsewhere in the gG that are either directly or indirectly capable of eliciting a type-specific response. The vaccine may alternatively be an insertion mutant vaccine utilizing the promotor of gG. In a preferred form DNA coding for equine influenza virus haemagglutinin antigen or other equine virus antigens including equine influenza neurimidase or nucleoprotein antigens or derivatives thereof are inserted into EHV4 or EHVl "downstream" of the gG promotor. In another preferred form DNA coding for any one, or a combination of, equine arteritis vims, equine rhinovirus and equine adenovirus is inserted into the EHV4 or EHVl "downstream" of the gG promotor. Alternatively, the gG deleted gene location could be used for insertion and expression of foreign genes driven by other foreign promoters. Numerous alternative vaccine products are included in the scope of the invention. The invention further provides an immunological test kit characterized by antigens in the form of envelope glycoproteins capable of distinguishing horses infected with equine heφesvirus 4 and equine heφesvirus 1. The antigens can be any of the envelope glycoproteins or epitopes as hereinbefore described but are most preferably EHV4 gG amino acids 287-382 and EHVl gG amino acids 288-350. Any subsequences of the above epitopes capable of eliciting type- specific responses are also particularly preferred as capture antigens. The invention further provides numerous immunological tests and methods utilizing the unexpected highly distinctive properties of the above described EHV4 and EHVl epitopes. In particular the invention provides an immunological test method comprising at least the following steps: - a) Antibody contained in horse serum is added to a filter paper disc and allowed to react with EHV4 gG or EHVl gG capture antigens; b) Following washing a second anti-species antibody conjugated to an enzyme marker is added to the filter paper and allowed to react with any speci ically bound horse antibody; c) After a further washing, an enzyme substrate capable of generating a signal is added. The invention further provides a method of testing for EHV4 and EHVl infected horses comprising the detection of wild type EHV4 and/or EHVl characterized by the presence of EHV4 gG and/or EHVl gG. The method also allows the testing for a horse vaccinated against EHV4 and/or EHVl by the detection of EHV4 and/or EHVl characterized by the absence of EHV4 gG and or EHVl gG. The method also allows the testing for a horse not infected with or vaccinated against EHV4 or EHVl by the detection of the absence of EHV4 gG and EHVl gG antibodies. The testing methods may use EHV4 gG and EHVl gG antigens in combination with other equine heφesvirus glycoproteins. In another aspect, the invention provides antibodies to the above described envelope glycoproteins capable of distinguishing equine heφesvirus 4 and equine heφesvirus 1. The antibodies are most preferably monoclonal and raised against the EHV4 gG epitope comprising the amino acid sequence 287 - 382, or subsequences thereof capable of eliciting a type-specific response. Similar monoclonal antibodies may be raised against the EHVl gG epitope comprising the amino acid sequence 285 - 350, or subsequences thereof capable of eliciting a type-specific response. In yet another aspect, the invention provides nucleic acid hybridization probes to the EHV4 and EHVl gG epitope nucleotide sequences. DETAILED DESCRIPTION OF THE INVENTION The invention will now be more fully described with reference to Figures 1 to 13 as follows: - Figure 1 Identification and characterisation of proteins found in the supernatant (S/N) of EHV4 and EHVl infected cell cultures, (a) EHV4 S/N proteins (E4 S/N) or EHV4 purified virion proteins (E4 VP) were separated on a 10% polyacrylamide gel and transferred to PVDF membranes. Mock infected cell culture supernatant (Mo S/N) was included as a control. The S/N proteins were probed with either a pool of monospecif ic, polyclonal post-EHV4 horse sera or a pool of 4 monoclonal antibodies (MAbs) directed to EHV4 gp2, gplO, gpl4 or pl8. The lane to the far right represents an flourograph of a PVDF membrane containing [ 14 C]glucosamine labelled EHV4 virion proteins. The EHN4 secreted proteins detected by the polyclonal sera are indicated by arrows and the major EHN4 glycoproteins are indicated at the right, (b) Flourographs of [ 1 C]glucosamine labelled E4 NP or S/Ν proteins after separation on a large polyacrylamide gel (16 x 16 x 0.75cm). Labelling of the major glycoproteins and the secreted products is as above, (c) Western blot of EHV4 S/Ν proteins probed with sera derived from SPF foals that were either immunized with EHVl (SPF foal 1), experimentally infected with EHNl (SPF foal 2a) and later cross-challenged with EHV4 (SPF foal 2b) or immunized with EHN4 (SPF foal 3) and with sera from two previously seronegative horses that were experimentally infected with EHV4 (post-EHN4 infection horses 1 and 2; E4 Abl and E4 Ab2). A pool of sera taken from the three SPF foals prior to immunization or infection is included (pre), (d) Western blot of S/Ν from cell line grown EHNl (El S/Ν) or mock infected cell cultures (Mo S/Ν) both probed with either a pool of post-EHNl sera which includes sera from foal 1 and foal 2a (El) or a pool of post-EHN4 sera which includes sera from foal 3 and post-EHN4 infection horse 2 (E4). Figure 2 Strategy for determining the nucleotide sequence of the US region EHN4 DΝA located near the internal repeat structure, (a) EHN4 genome showing unique long (UL) and unique short (US) regions as well as the internal and terminal repeat sequences that bracket the US region (IRs and TRs respectively), (b) Eco Rl retriction endonuclease map of the EHN4 genome, (c) Expansion of the Eco Rl G fragment showing Sma I (S) and Hind III (H) cleavage sites. The approximate locations of sequences covered by deletion clones are indicated by the arrows, (d) Location and orientation of the five major open reading frames (ORFs). The ORFs are given HSN designations (in brackets) if homology Was established. Figure 3 Nucleotide sequence and predicted amino acid sequence of ORF4 and flanking regions. Amino acids are given in single letter code and are numbered, from the first methionine residue, on the right. The TATA box, Pst 1 site, polyadenylation signal and GT-rich region following the polyadenylation signal are underlined sequentially. Potential asparagine (N)-linked glycosylation sites (N-X-S T) are indicated by asterisks (*) and the proposed proteolytic cleavage site at amino acid residue 19 is indicated by a slash (/). Figure 4 Expression of EHV4 gG in E. coll (a) Western blots of EHV4 glycoprotein G-glutathione S-transferase fusion protein (gG) which was produced in E. coli transformed with a EHV4 gG pGEX-3X recombinant plasmid and prepared by purification using glutathione-agarose beads. GST only (gst) was included as a control and was prepared by transformation of E. coli with parental plasmid pGEX. The PVDF membranes were probed with either a pool of post- EHV4 sera (E4-Ab) which included sera from an SPF foal immunized with EHV4 (SPF foal 3) and a previously seronegative horse that was experimentally infected with EHN4 (post-EHV4 infection horse 2) or a pool of post-EHNl sera (El-Ab) which included sera from SPF foals that were either immunized (SPF foal 1) or experimentally infected with EHNl (SPF foal 2a). The 70K gG-GST fusion protein is arrowed, (b) Western blots of gG-GST fusion protein (gG), GST only (gst) and EHN4 secreted proteins derived from the supernatant of EHN4 infected cell cultures (S/Ν) probed with antibody from post-EHV4 infection horse 2 that had been affinity purified from selected portions of Western blots that contained either the gG-GST fusion protein (gG-Ab) or the 63K EHN4 secreted protein (63K-Ab). The 70K gG-GST fusion protein and the 63K secreted protein are arrowed. Figure 5 (A) Alignment of the amino acid sequences of EHV4.405/76 gG with EHVl.Ab4p gG as determined by Telford et al (1992). The amino acid numbers are indicated on the right. Predicted signal sequence and transmembrane sequence at the Ν- and C-termini respectively are indicated by the dashed lines. Potential Ν-linked glycosylation sites (Ν-X-S/T) are indicated by the balloons with the filled balloon indicating a site conserved in the gG homologues of PRV, HSN2 and ILTN. The cysteine residues conserved between EHN4 gG and EHNl gG and also in the gG homologues of PRV, HSN2 and ILTN are boxed. A near perfect repeated sequence in EHN4 gG is indicated by the arrows. (B) Hydropathic analysis of EHV4 gG (top panel) and EHVl gG (bottom panel) amino acids according to the algorithm by Hopp and Woods (28). The -axis represents the amino acid number and the Y-axis considered hydrophilic and likely to comprise antigenic sites. The most variable regions of the two sequences are overlined and the amino acid numbers shown. Figure 6 Strategy for cloning EHN4 gG (A) and EHNl gG (B). The Eco Rl restriction endonuclease map of the EHN4 genome and the Bam HI restriction endonuclease map of the EHNl genome are shown at the top of panels (A) and (B) respectively. The Eco Rl G fragment of the EHN4 genome and the Bam HI D fragment of the EHNl genome are expanded. Sma I (S), H d III (Η) and Pst I (P) cleavage sites are indicated for EΗN4 Eco Rl G while Pst I (P) cleavage sites are indicated for EHNl Bam HI D. The location and orientation of the known open reading frames contained within these fragments are indicated by the arrows. The EHNl ORFs are numbered according to the designations of Telford et al while their EHN4 homologues are given the same numbers but distinguished using a prime. HSV designations are given (in brackets) if homology has been established. The bottom of each panel shows a schematic representation of the various gG molecules expressed by the recombinant plasmids pEG4.1 and pEG4var (A) and pEGl.l, pEG1.2 and pEGlvar (B). Predicted signal sequences and transmembrane domains are indicated by the open and closed boxes respectively and the C-terminal variable regions of EHN4 gG (amino acids 287-382) and EHVl gG (amino acids 288-350) are shown by the cross-hatching. Figure 7 Coomassie brilliant blue staining of GST-gG fusion proteins expressed in E. coli transformed with parental pGEX, pEG4.1, pEGl.l or pEG1.2 following SDS-PAGE. Two samples were prepared for each clone comprising the pellet remaining after solubilization of the E. coli (left strip) and the purified GST-fusion protein (right strip). The location of the GST-fusion proteins at 27K (pGEX), 70K (pEG4.1), 60K (pEGl.l) and 72K (ρEG1.2) are indicated by the asterisks. Figure 8 Western blot of GST-gG fusion proteins expressed in E. coli transformed with parental pGEX, pEG4.1, pEGl.l or pEG1.2. Membranes were probed with pooled SPF foal 3 and post-EHN4 Νo.2 horse sera (post-EHV4-Ab) or pooled SPF foal 1 and SPF foal 2a horse sera (post-EHVl-Ab). All samples were run on the same SDS-PAGE gel. Approximate Mr values of GST-gG fusion proteins produced by pEG4.1 (EHV4 gG), pEGl.l (EHVl gG (aal-310)) or pEG1.2 (EHVl gG) are indicated to the right. Figure 9 Coomassie brilliant blue (Coomassie) and Western blot of GST-gG fusion proteins expressed in E. coli transformed with parental pGEX, pEG4var or pEGlvar. Membranes were probed with pooled SPF foal 3 and post-EHV4 No.2 horse sera (EHV4 only-Ab) or pooled SPF foal 1 and SPF foal 2a horse sera (EHVl only-Ab) and pooled SPF foal preexposure sera (preexposure-Ab). Approximate Mr values of GST fusion proteins produced by pGEX (GST only), pEG4var (E4 gG aa287-382) or pEGlvar (El gG aa288-350) are indicated to the right, lμm gm of fusion protein was loaded to each lane. Figure 10 Titration curves showing reactivity in ELISA of SPF foal 1, SPF foal 2a, SPF foal 3 and post-EHN4 Νo.2 horse sera with the recombinant proteins GST only (open circles), GST-EHV4 gG (amino acids 287-382; open squares) and GST- EHV1 gG (amino acids 288-350; closed squares) produced by E. coli transformed with pGEX, pGE4var, or pEGlvar respectively. Figure 11 The four numbered circles are spots on the filter paper impregnated with the designated antigen. In this format a horse immunized with an EHV4 and/or EHNl gG gene deleted virus would not contain antibody to either gG so there would be no colour change in the upper two dots. However, the horse would contain antibody to many (all) other antigens of EHN4 and EHVl and hence the lower left whole EHN4 (or EHNl) spot would give a colour change- indicative of a vaccinated but not an infected horse. An example of this type of test is marketed by Agritech Systems Inc under the trade mark "CITE". Figure 12 This test could also be formatted in, for example, the familiar 96-well microprocedure plate (four wells of which are represented) in which alternate triplet wells would contain EHV4 gG, EHNl gG and either EHV4 or EHVl whole virus absorbed to the bottom of the well. Appropriate other negative and positive control wells or spots, in the case of the filter paper test, could be included to further validate the test. The fourth well shown contains an uninfected cell lysate as an example of a negative control. An example of this type of test is marketed by Agritech Systems Inc under the trade mark "PETCHEK". SUMMARY OF DETAILED DESCRIPTION Equine heφesvirus 4 (EHV4) glycoproteins of Mr 63K and 250K were identified in the supernatant of infected cell cultures. The 63K glycoprotein was type-specific, that is, it reacted with monospecific sera from horses that had been immunized or infected with EHN4, but not with monospecific sera from horses immunized or infected with EHNl, a closely related alphaheφesvirus. It was proposed that the secreted protein may, in fact, be the homologue of similarly secreted glycoproteins of heφes simplex virus 2 glycoprotein G (HSN2 gG) and pseudorabies virus (PRN) gX, which is the homologue of HSN2 gG notwithstanding the highly similar nature of EHN4 and EHNl glycoprotein when compared to the HSN and PRN glycoproteins which would teach away from the expectation of such a result. The US region of the EHN4 genome, toward the internal repeat structure, was sequenced. Four open reading frames (ORFs) were identified of which ORF4 showed 52% similarity to the gene encoding PRN gX in a 650 nucleotide region. ORF4 coded for a primary translation product of 405 amino acids which has a predicted size of 44 kilodaltons (K). The amino acid sequence of ORF4 showed 28% identity with PRN gX and 16% identity with HSN2 gG, although significantly greater identity was observed in the Ν-terminal region including the conservation of 4 cysteine residues. Accordingly, we designate ORF4 as EHV4 gG. The predicted amino acid sequence of the EHN4 gG showed characteristics of an envelope glycoprotein. Expression of the entire EHV4 gG gene in the bacterial expression vector pGEX-3X produced a type-specific fusion protein of Mr 70K of which the gG portion comprises 43K. Antibody that was affinity purified from selected portions of Western blots containing the 70K gG fusion protein reacted with the 63K secreted glycoprotein. Conversely, antibody affinity purified to the 63K secreted product reacted with the 70K gG fusion protein. These results showed that the EHV4 63K secreted glycoprotein was EHV4 gG, the third alphaheφesvirus gG homologue known to be, at least in part, secreted. The antigenicity of full and partial length EHV4 gG and EHNl gG molecules expressed in E. cø/i ' .was determined. Fusion proteins comprising full length EHN4 gG (405 amino acids) or EHNl gG (411 amino acids) reacted strongly and type-specifically with pooled post-EHN4 only or -EHVl only horse sera respectively. A fusion protein containing amino acids 1-310 of EHVl gG was not immunoreactive with the post-EHNl horse sera thereby localising the immunoreactive epitope(s) to the C- terminal portion of the molecule. It was postulated that the type-specific epitopes were located within the highly variable regions comprising amino acids 287-382 of EHN4 gG and 288-350 of EHVl gG. Fusion proteins expressing these variable regions reacted strongly and type-specifically with a panel of post-EHN4 and/or post-EHNl horse sera. These fusion proteins, which were easily purified and produced in large amounts, provided the basis for the development of diagnostic serological assays such as ELISA to distinguish EHV4-, EHNl- and dual-infected horses. MATERIALS AND METHODS Cells and viruses Virus strains EHV4.405 76 and EHVl.438/77 at passages 5 and 3 were grown in equine fetal kidney (EFK) cells respectively as described elsewhere. Purification of virions was also carried out as described previously. Infected cell culture supernatant was prepared by infecting cells as described previously except that after virus adsoφtion the cells were washed twice with Hank's balanced salt solution before the addition of serum free maintenance medium. The supernatant was collected at 16h post infection, clarified at 2,500 X g for lOmins then centrifuged at 100,000 X g for 60mins and stored at -20°C until required. Antibodies MAbs 1G12, 13A9, 3F6 and 20C4, directed against EHN4 gp2, gplO, gpl4 (gB, large subunit) and gpl8 (gD) respectively, were provided by G. P. Allen (University of Kentucky, Lexington, KY, USA). Monospecific antisera to EHN4 and EHVl were obtained from colostrum-deprived, SPF foals after a series of immunizations and challenges with either EHVl (foal 1) or EHN4 (foal 3). Post-EHN4 only and post- EHNl only horse sera were obtained from colostrum-deprived, specific-pathogen-free (SPF) foals after a series of immunizations and challenges with either EHVl (foal 1 serum) or EHN4 (foal 3 serum). Another post-EHNl only horse serum was obtained from a third SPF foal that was experimentally infected with EHNl (foal 2a serum). This foal was later cross-challenged with EHN4 (foal 2b serum). Post-EHV4 only sera were also obtained from three previously seronegative horses that were experimentally infected with EHN4, termed post-EHN4 Νos. 1, 2 and 3. Sera were also obtained from two mares that had aborted as a result of EHNl infection either 5 weeks (post abortion mare 1) or 1 year (post abortion mare 2; see Table 2). A serum was also obtained from a foal which had been experimentally infected intrauterinally with EHN2 and which possessed high antibody titers to this virus. Western blots Sodium doedecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and electrophoretic transfer of viral proteins to Immobilon polyvinylidene fluoride (PVDF; Milipore) membranes were carried out as described previously . The PVDF membranes were cut into strips and probed in either 2ml wells or small trays, depending on the size of the membrane strip, with either, MAbs diluted 1/1000 in antibody diluent (phosphate-buffered saline (pH 7.5) containing 0.05 % (v/v) Tween- 20 (PBST) with 5 mg ml bovine serum albumin (BSA 5 ) and 5% goat serum), polyclonal sera diluted 1/100 or affinity purified antibody (as described below) for 1 h at room temperature. Membranes were then washed for 15mins with PBST. The primary antibody was detected with either a 1/1000 dilution of affinity purified rabbit anti-mouse IgG (Dako Immunoglobulins) or a 1/300 dilution of an affinity purified goat anti-horse IgG (Kirkegaard and Perry Laboratories Inc.), both conjugated with horseradish peroxidase, where appropriate. The blots were washed again with PBST and developed using a 3'3'diaminobenzidine (DAB) substrate (Sigma). ELISA ELISA's were carried out in 96 well polyvinyl chloride microtitre plates (Nunc- Immunoplate Maxisoφ). The plates were washed 4 times between each step with PBST and incubated with volumes of lOOμl/well on a shaker for lh unless otherwise stated. Wells were coated with approximately lOμg ml purified virus, 0.5μg/ml glutathione-S transferase (GST; see below) fusion protein or cell culture supernatant diluted 1/5 in 0.05 M carbonate-bicarbonate buffer (pH 9.6) overnight at 4°C. Unoccupied sites were blocked by incubation for 2h with BSA j PBS containing 5% goat serum (200 μl/well). Serial dilutions of polyclonal horse sera were then made in the wells using BSA j PBST containing 5% goat serum as diluent. Horseradish peroxidase-conjugated affinity purified goat anti-horse IgG (Kirkegaard and Perry Laboratories Inc.), diluted 1/1000 in antibody diluent, was added to each well. Plates were developed using a soluble TMB substrate (Sigma) and read spectrophotometrically, after 15mins incubation at room temperature without shaking, at 450 nm using a Titertek Multiskan MC3 (Flow Laboratories). DNA cloning and sequencing Cloning of the subfragments of the EHV4 Eco Rl G fragment has been described previously. E. coli strain DH5α was used to maintain the clones HS (2 kb) and G19 (3.4 kb). In order to determine the complete sequence of the clones a nested set of deletions was generated for each strand using the Erase-a-base system (Promega). After religation, the deleted plasmid DNA was used to transform competent E. coli (DH5α). The relevant deletion clones were selected and sequenced using the dideoxy chain termination method using modified T7 DNA polymerase (Pharmacia, Uppsala, Sweden) and [ 35 S]-dATP (Amersham). Sequencing reactions were electrophoresed in 6% polyacrylamide wedge gels. In addition, internal oligonucleotide sequencing primers were synthesized and used to fill in gaps in the sequence. DNA sequence analysis DNA sequence data analysis was performed using the Geneworks software package (IntelliGenetics, Mountain View, California, USA). Sequence similarity searches were made in the GenBank database using the FAST A programs of Pearson and Lipman (1988). Preparation of EHV4 gG and EHVl gG recombinant plasmids. The bacterial expression plasmids pGEX-3X or pGEX-2T (AMRAD, Hawthorn Australia) were used to express the EHV4 gG and EHNl gG genes from strains 405/76 and 438/77 respectively. Restriction endonuclease digestion and ligation of DΝA as well as CaCl 2 transformation of competent E. coli were carried out according to Sambrook et al. For the derivation of clones pEG4var and pEGlvar (see below) transformation was performed using the Gene-Pulser Electroporator (Bio-Rad). The EHVl.438/77 Bam HI D fragment, which encompasses much of the EHNl US region (Fig. 6), was cloned into pUC-19 following purification of the fragment from an agarose gel slice using Prep A Gene matrix and buffers (Bio-Rad). The nucleotide sequence of the first and last 200-300 bases of each recombinant expression plasmid was determined to ensure correct identity, orientation and frame of the cloned gene (data not shown). The following recombinant plasmids (see also Fig. 6) were constructed: (i) pEG4.1 which was derived from a pUC-18 deletion clone, designated 18S/E, which was derived in the course of DNA sequencing by utilizing a Pst I site located just upstream from the start of the gG gene. The plasmid contained a 1.4 kilobase pair insert within which was the entire EHV4 gG gene (1,215 nucleotides) plus three nucleotides upstream from the gG initiation codon and 201 nucleotides downstream from the gG gene (Figs. 2, 3 and 6). After digestion of 18S/E with Bam HI and Eco Rl, the insert was excised from an agarose gel following electrophoresis, purified using Prep A Gene matrix and buffers (BioRad), and ligated into the Bam HI/Ec Rl site of the bacterial expression plasmid pGΕX-3X such that the 5'-end of the gG gene was adjacent to and in frame with the 3'-end of the fusion protein glutathione S- transferase (GST). (ii) pEGl.l contains a 933bp insert encompassing the first 930bp of the EHVl gG gene plus three base pairs upstream from the initiation codon. This plasmid was derived from an EHVl.438/77 Bam HI D clone utilizing Pst I sites located at either end of the insert, creating blunt ends with Klenow enzyme and dNTP's and ligating into the Sma I site of pGEX-3X. (iii) pEG1.2 contains the entire EHVl gG gene of l,233bp. The insert was derived by polymerase chain reaction (PCR) amplification of the EHNl gG gene using Vent polymerase (New England Biolabs) at 35 cycles of 94° x 20sec, 48° x 20sec, 72° x 2min. The EHNl.438/77 Bam HI D plasmid which includes the entire gG gene (Fig. 6) was used as template DΝA and the synthetic oligonucleotide primers, which encompassed the first and last 17 nucleotides the EHNl gG gene and included Bam HI sites (in bold type below) plus a 2 base overhang, were as follows: forward 5'- cgggatccatgttgactgtcttagc-3 1 ; reverse 5'-cgggatcctaagcaacgtactcaag-3'. It was not possible to clone the 1.23 kb PCR product directly into the Bam HI site of pGEX-2T presumably because the Bam HI recognition sites close to the end of the fragment were not readily digested. As a result, the fragment was blunt ended using Klenow DNA polymerase (Pharmacia) and dNTP's followed by phosphorylation using polynucleotide kinase and then cloned into the Sma I site of pUC-19 . Digestion of the pUC-19/EHVl gG clone with Bam HI released the 1.23kb fragment which was then cloned into the Bam HI site of pGEX-2T. (iv) pEG4var contains nucleotides encoding EHV4 gG amino acids 287 to 382 and was constructed by PCR amplification (35 cycles of 94° x 20sec, 50° x 20sec, 72° x 30sec) using pEG4.1 DNA as template and the following primers: forward 5'- gaaaatgaaacctacag-3'; reverse 5'-tggaggccatgcaacac-3'. The fragment obtained was cloned directly into the Sma I site of pGEX-3X. (v) pEGlvar contains the nucleotides encoding EHNl gG amino acids 288-350 and was constructed by PCR amplification as described above for pEG4var except that EHNl Bam HI D was used as template DΝA and the primers were as follows: forward 5 ' -ggtgacgaaacatacga-3'; reverse 5'-tggatgccgttcgacgc-3'. GST-fusion protein preparations • The pGEX plasmid was chosen for expression because of the ease with which the GST-fusion protein can be affinity purified by utilizing agarose beads coated with covalently attached reduced glutathione (Sigma), a strong ligand for GST. Several colonies containing the recombinant plasmid were isolated and protein was prepared by a small-scale GST-fusion protein purification method based on that of Smith and Johnson (1988). Briefly, single colonies were inoculated into 5ml broth cultures and incubated for 4h at 37°C after which time 5μl of a 1M IPTG stock solution was added and the cultures further incubated for 2h. The bacteria (1.5ml of culture) were pelleted by centrifugation at 12, OOOg for 2mins, washed once with 1.5ml PBS and made up to 0.5ml with PBS containing 1% Triton X-100. The cells were sonicated at a low setting (2 x lOsecs) and centrifuged as above. Glutathione agarose beads (75μl of a 50% suspension in PBS; Sigma) were then added to the supernatant and the mixture left at 4°C for 15mins with intermittent mixing. The beads were centrifuged at 12, OOOg for 30secs, washed 3 times with 1.5 ml of PBS and finally resuspended in 200μl of sample buffer prior to SDS-PAGE. Affinity purification of antibody from selected portions of Western blots Antibody was affinity purified from selected portions of Western blots by eluting antibody at low pH based on the method of Beall and Mitchell (1986). Briefly, proteins were separated by SDS-PAGE after first loading either EHN4 supernatant, diluted 1/2 in double strength reducing buffer (200μl), or recombinant gG protein (200μl) into a 5cm well. Following the transfer of proteins to PVDF membranes, selected portions of the membranes were cut such that the protein of interest was contained in the cut out portion. To isolate the 63K secreted protein a section containing proteins from 50K-70K was cut out and to isolate the 70K recombinant GST-gG protein a section containing proteins from 65K-75K was cut out. Cut out membrane portions were blocked to prevent non-specific binding by incubating for lh in BSAjPBST containing 5% goat serum. EHN4 antiserum diluted 1/10 in BSA 5 PBST containing 10% goat serum and 10% fetal bovine serum (with total volume of 2ml) was then added to the cut out membrane for 2h with constant rocking. The membranes were washed extensively for 30mins with PBST. Antibody was eluted from each membrane using 2ml of 0.1M glycine, 0.15M ΝaCl (pH 2.6) for 3 mins. The eluate was adjusted to pH7.5 by addition of 300μl Tris-HCl (pH 7.5), diluted 2-fold in BSA^BST containing 5% goat serum and either stored at -70°C or used immediately, with no further dilution, to probe Western blots. EXAMPLE ONE Identification of secreted, type-specific glycoproteinζs) of EHV4 EHN4 and EHNl infected cell culture supernatants were examined for the presence of secreted viral proteins. Fig. la shows a Western blot of EHN4 infected cell culture supernatant and mock infected cell culture supernatant probed with a pool of post- EHV4 horse sera. An immunodominant region is evident in the EHN4 supernatant at approximately 200K and 63K while no such proteins were seen in the mock supernatant. The supernatant proteins were also probed with a pool of MAbs directed to gp2, gplO, gpl4 (large gB subunit) and gpl8 (gD) (Fig. la). Only when the membranes were left in TMB substrate for a prolonged period could these proteins be visualized in the supernatant, indicating that they were all present in low abundance. Nevertheless, gp2 appeared co-migratory with the larger of the secreted products while none of the other three glycoproteins was co-migratory with the 63K secreted product. The small subunit of the gB heterodimer (62K), a major EHN4 glycoprotein which migrates to a position on an SDS-PAGE gel just above gpl8 (56K), has a Mr similar to the smaller secreted product (Fig. la). To examine the relationship between these two proteins and to determine if the secreted products were glycoproteins, [ 1 C]glucosamine labelled virion proteins and supernatant proteins were subjected to SDS-PAGE on a large (16 cm X 16 cm X 0.75 mm), 10% polyacylamide gel (Fig. lb). Glycoproteins at approximately 250K and 63K were evident in the EHN4 supernatant. A small amount of a glycoprotein co-migrating with gpl3 was also observed in the EHN4 supernatant suggesting either that this glycoprotein was also secreted, albeit at low levels, or that low levels of all the glycoproteins were present in the infected cell culture supernatant possibly as a result of lysis of some infected cells and that gpl3, being the most heavily labelled, was the only glycoprotein easily observed. Both the 250K and 63K products did not appear to exactly co-migrate with viral glycoproteins gp2 and small gB subunit (Fig. lb). Unlike the small gB subunit, the 63K secreted product was identified as a rather diffuse glycoprotein band that did not label particularly well with [ 1 C]glucosamine. Furthermore, as the EHV4 gB heterodimer is derived from a single gene and is covalently linked by disulphide bonds, it is unlikely that the small gB subunit would be secreted in the absence of the large gB subunit. It appeared likely, therefore, that both the 250K and 63K secreted products were previously undefined glycoproteins of EHN4. The type-specificity of the secreted products was examined. In Western blot the smaller product (63K) was shown to be completely type-specific as it reacted strongly with monospecific horse sera from SPF foals or previously seronegative horses that were either immunized or infected with EHN4 but not with sera from SPF foals that were either immunized or infected with EHNl (Fig. lc). Of particular note was the seroconversion of foal 2 from a negative to positive reaction in Western blot to the 63K secreted product after this foal, which was initially infected with EHNl (foal 2a serum), was cross-challenged with EHN4 (foal 2b serum). The 250K secreted product appeared less immunodominant than the 63K secreted product. However, this may be misleading as the 250K secreted product may not have transferred to the PVDF membranes as efficiently as the 63K secreted product. The ELISA data presented in Table 1 shows that: (a) The monospecific horse sera, mostly obtained from SPF-foals (described above), showed significant ELISA titres of between 10 3 - 6 (4,000) and 10 4 - 3 (20,000) when tested against the virus to which they were exposed; either EHNl or EHN4. (b) Each serum contained antibody which was cross-reactive with the heterologous virus such that its ELISA titre against either virus was very similar, (c) The EHN4 secreted produces) produced an EHN4 specific response in ELISA i. e. } when the EHN4 supernatant was used to coat the wells of ELISA plates post-EHN4 sera showed titres of between 500 and 1000 whereas post- EHNl sera showed titres of between 20 and 40. This not only confirmed the Western blot results (Fig. lc) but indicated that any discontinuous epitopes on the secreted produces), that would be presented in this type of assay but not in Western blot, were also type specific; (d) The EHNl supernatant did not react significantly with any serum indicating that EHVl did not secrete a protein that was detectable with these immune reagents. DNA sequence analysis Clones carrying fragments of the US region close to the internal repeat region of the EHV4 genome were sequenced (Fig. 2). Analysis of 5451 nucleotides showed four complete major ORFs, two rightward and two leftward, and one partial ORF in the rightward orientation (Fig. 2). Similarity searches of the GenBank database revealed that ORF2 was most homologous to HSV1 US2, ORF3 to PRV US1 (protein kinase) and its homologue HSV1 US3, ORF4 to PRV US2 (gX), and ORF5 to HSV1 US5 (gJ). No statistically significantly homologous gene was observed for ORF1. Analysis of ORF4, the gene showing similarity to the PRV gX gene, is described below while the other genes are not discussed further in this manuscript. The sequence of ORF4 and flanking regions is shown in Fig. 3. Examination of the flanking sequences of the ORF4 gene revealed: (a) A TATA box, TATAAA, beginning 79 nucleotides upstream from the initiation codon (position -79) aligns well with the PRV gX TATAAA which is at position -65 (Rea et al., 1985) (b) A poly (A) signal AATAAA located 124 nucleotides downstream from the termination codon (c) A GT-rich region beginning 168 nucleotides downstream from the termination codon. The coding region comprises 1215 nucleotides coding for 405 amino acids. The N- terminus of the predicted amino acid sequence has some features characteristic of a membrane insertion (signal) sequence including hydrophobic amino acids from Leu-2 to Gly-19 (Fig. 3) followed by a potential peptidase cleavage site between Gly-19 and Arg-20 (Fig. 3). However, there is no positively charged residue(s) to the left of the hydrophobic amino acids which is common for heφesvirus glycoprotein signal sequences. The predicted cleavage site is preceded by a helix breaking residue, Gly- 16, which is usual for signal sequences. Further evidence for this location of the cleavage site is shown by comparison of the 9 amino acids of ORF4 which directly follow the predicted cleavage site with the corresponding 9 amino acids of PRN gX, the protein which showed most similarity to ORF4 (see below), in which 6 amino acids directly align including Cys-27 (EHN4) with Cys-28 (PRV). The C-terminal 18 amino acids are hydrophobic in nature and this region may comprise the glycoprotein transmembrane domain (Fig. 3). The sequence contains 5 potential asparagine-linked (Ν-linked) glycosylation sites, which require the motiff Asn-X- Ser/Thr where X is not a proline residue, occurring at positions 83, 138, 174, 221 and 288 (Fig. 3). Only two proteins in the GenPept protein database showed significant identity with the predicted amino acid sequence of ORF4, PRN gX (the HSN gG homologue) and HSN2 gG. ORF4 showed 28% overall amino acid identity with PRN gX although significantly greater identity was apparent toward the Ν-terminus. The similarity of the two sequences was further evidenced by the conservation of 5 cysteine residues, 4 located in the Ν-terminal region, and by the occurrence of 8 separate regions of 4 to 6 identical residues. There was also a limited identity (16%) observed between ORF4 and HSN2 gG but again greater identity was observed toward the Ν-terminus including conservation of the same 4 cysteine residues as conserved with PRV gX. The EHV4 gG Ν-linked glycosylation site at position 138 was conserved in both PRV gX and HSN2 gG, suggesting that this site at least is probably utilized, while those at positions 83 and 221 were conserved in PRV gX only. On a basis of the similarity observed between ORF4 with PRV gX and with HSV2 gG, ORF4 was designated EHN4 gG. Expression of the EHV4 gG gene to identify 63K secreted product as EHV4 gG A 1.4 kilobase pair subfragment which contained the entire gG gene (1215 base pairs) as well as five base pairs upstream and 201 base pairs downstream of the gG gene was cloned into pGEX-3X ensuring that the gG gene was in frame with the GST fusion protein gene. The resulting pGEX-EHV4-gG recombinant clone was termed pEG4.1. The fusion protein subsequently expressed by pEG4.1 transformed cells was, after purification on glutathione-agarose beads, identified in Western blot using a pool of post-EHN4 horse sera (Fig. 4a). This protein had a Mr of 70K; the gG portion constitutes 43K as the Mr of GST is 27K. The 70K fusion protein did not react in Western blot with a pool of post-EHNl SPF-foal sera (Fig. 4a). A corresponding band was not observed in the control preparations from cells transformed with pGEX only. To determine if the EHV4 63K secreted product described earlier was in fact gG, antibody was affinity purified from selected portions of Western blots that contained either the 63K secreted product or the 70K EHN4 GST-gG fusion protein. Using these two affinity purified antibody preparations to probe Western blots it was shown that both antibody preparations reacted strongly with the 63K EHV4 secreted product and the 70K EHV4 gG fusion protein (Fig. 4b). This confirmed that gG was the 63K product found in the cell culture medium of infected cells. It was also apparent that the 250K secreted product was not related to the 63K secreted product as neither antibody preparation reacted with this glycoprotein (Fig. 4b). A glycoprotein at 63K was also detected on Western blots of purified EHV4 virions using both affinity purified antibody preparations (data not shown). Comparison of the sequences of EHV4 gG and EHVl gG. The nucleotide sequences of EHNl gG from two different strains, EHNl.Ab4p, and EHNl.KyA, and the EHV4 gG sequence of strain EHN4.405/76 (described here) and have not been compared. The two EHNl gG sequences differed from each other in three nucleotides all located toward the 3'-terminus of the gene and all resulting in frame shifts (data not shown). A missing guanosine at the first position of codon 335 in EHNl.KyA gG results in a different codon usage from EHNl.Ab4p gG until an additional adenosine in EHVl.KyA gG at the first position of codon 356 restores the two sequences to identical codon usage. Also, a missing cytidine at the third position of codon 374 in EHVl.KyA gG produces a stop codon whereas EHNl.Ab4p gG reads to codon 411. Therefore the two published sequences of EHVl gG not only differ in their amino acids at positions 335-356 but are of different lengths with EHNl.KyA gG possessing 373 and EHVl.Ab4p gG 411 amino acids. In an attempt to reconcile these differences we determined the nucleotide sequence of the 5'- and 3'-termini (approximately 300 nucleotides at each end) of recombinant plasmid pEG1.2 which contains the entire EHNl gG gene derived from our prototype EHV1 strain 438/77 (data not shown). The sequence obtained, which covered all the ambiguous nucleotides, was identical to that of the EHNl.Ab4p gG sequence. Furthermore, the size of the GST-fusion protein produced by pEG1.2 (72K) was slightly larger than the GST-fusion protein produced by pEG4.1 (70K), an expression plasmid containing the entire EHN4.405/76 gG gene which codes for a protein of 405 amino acids (Fig. 3). This is consistent with EHV1.438/77 gG, like its EHVl.Ab4p counteφart, comprising 411 amino acids. A comparison of the predicted amino acid sequences, of EHN4.405/76 gG and EHVl.Ab4p gG is shown in Fig. 5a. These glycoproteins show an overall identity of 58% with the C-terminal region generally showing considerably more divergence than the Ν-terminal region. Amino acids 1-286 of EHV4 gG and 1-287 of EHNl gG show an identity of 75% whereas the apparently corresponding C-terminal regions of EHN4 gG, amino acids 287-382, and EHVl gG, amino acids 288-350, have diverged widely and exhibit little amino acid identity (Fig. 5a). Another region of considerable diversity is a 25 amino acid region, residues 32-57 of both viruses, in which only 9 amino acids (36%) are identical. The nucleotide sequences of EHN4 gG and EHNl gG also show considerable divergence in the two above mentioned variable regions (data not shown). Using the protein algorithm of Hopp and Woods both divergent regions are predicted to encompass antigenic sites (Fig. 5b). EHV4 gG and EHVl gG each has 9 cysteine residues in their respective predicted extracellular domains all which are conserved between the two viruses. Four cysteine residues located toward the Ν-terminus are conserved with pseudorabies virus (PRV) gG (gX), HSV2 gG and infectious laryngotracheitis virus (ILTV) gG (gX) (Fig. 5a). The predicted extracellular domain also contains five and six potential N-linked glycosylation sites for EHV4 gG and EHVl gG respectively. The three N-linked glycosylation sites at positions 83, 138 and 221/222 (EHV4/EHV1) that are conserved between EHV4 gG and EHVl gG are also conserved in PRN gG (gX) while the site at position 138 is also conserved in HSV2 gG and ILTV gG (gX) (Fig. 5a). The C-terminal variable region of EHN4 gG (amino acids 287-382) also possesses a repeated sequence of 9 amino acids MKΝΝPXYSE, where X is an isoleucine in the first repeat and a valine in the second, which is separated by 18 amino acids (Fig. 5a). Expression of EHV4 gG- and EHVl gG-fusion proteins. E. coli transformed with recombinant pGEX plasmids pEG4.1, pEGl.l or pEG1.2 express GST-fusion proteins associated with either entire EHN4 gG (405 amino acids), partial EHVl gG (amino acids 1-310) or entire EHNl gG (411 amino acids) respectively (Figs. 6, 7 and 8) . The fusion proteins were purified and assessed for their capacity to bind to antibody in pools of post-EHN4 only or post-EHVl only horse sera (Figs. 7 and 8; Table 2). It was evident from Coomassie Brilliant Blue stained SDS-PAGE gels that pEG4.1, pEGl.l and pEG1.2 produced stable fusion proteins of approximately 70K, 60K and 72K respectively (Fig. 7). However, unlike GST alone these recombinant GST-fusion proteins were largely insoluble and remained in the cell pellet after solubilization (Fig. 7). Nevertheless, adequate amounts of the fusion proteins were purified for Western blot analysis. Pooled post-EHN4 only horse sera reacted strongly with pEG4.1 fusion protein but not with pEGl.l or pEG1.2 fusion proteins (Fig. 8). Conversely, pooled post-EHNl only horse sera showed strong reactivity with pEG1.2 but not with pEGl.l or pEG4.1. Therefore, it was apparent that EHN4 gG- and EHNl gG-fusion proteins possessed strong type-specific, presumably continuous epitope(s). It also appeared as though these epitope(s) were located in the C-terminal regions of the glycoproteins as pEGl.l, which expressed amino acids 1-310 of EHNl gG, was not antigenic whereas pEG1.2, which expressed amino acids 1-411 of the same protein, was a strong antigen. The insolubility of pEG4.1, pEGl.l and pEG1.2 fusion proteins meant that relatively large amounts (approximately 50μl (1/4) of one small-scale fusion protein preparation) of purified GST-fusion protein was required. As a result some contaminating E. coli protein bands were evident in the Western blot shown in Fig. 8. It was considered most likely that these type-specific, continuous epitope(s) were located in the C-terminal variable regions of EHN4 gG (amino acids 287-382) and EHVl gG (amino acids 288-350). To show this as well as to produce more soluble antigens that are able to be purified in large amounts two pGEX-3X clones, termed pEG4var and pEGlvar, which express the corresponding variable regions of EHV4 gG and EHNl gG respectively were constructed. The GST-gG fusion proteins produced by pEG4var and pEGlvar were highly soluble as reflected by the ease of purification from E. coli lysates (Fig. 9). These antigens were also strongly type-specific in Western blot using pooled post-EHN4 only or post-EHNl only horse sera thereby confirming that the location of type-specific epitopes was within these variable regions (Fig. 9). An ELISA was developed using the recombinant gG antigens produced by pEG4var and pEGlvar. Fig. 10 shows the titration curves obtained for the four polyclonal horse sera used as the pooled sera to produce the Western blots described above. Post-EHN4 only (foal 3 and post-EHN4 No. 2) or post-EHVl only (foal 1 and foal 2a) horse sera showed a type-specific serological response against the GST-EHV4 gG or -EHVl gG fusion proteins respectively. The slight reactivity observed at low dilutions for foal 3 and post-EHV4 No. 2 sera against GST-EHVl gG and GST-only was probably due to reactivity against contaminating E. coli proteins which would be present at low (and variable) levels in the antigen preparations as no cross -reactivity was observed for these sera with GST-EHVl gG or GST-only in Western blot (Fig. 9). Several other horse sera were tested in ELISA for reactivity to the GST-gG fusion proteins produced by pEG4var or pEGlvar and the titres obtained are shown in Table 2. From the data shown in Table 2 it was evident that: (a) The post-EHV4 or post-EHVl only horse sera showed significant ELISA titres of between 4,000 and 21,000 when tested against the virus to which the horses were exposed, (b) Each serum contained antibody which was cross -reactive with the heterologous whole virus such that its ELISA titer against either virus was very similar, (c) The GST-EHV4 gG and -EHVl gG fusion proteins reacted type-specifically against all the known post-EHV4 only and post-EHVl only sera tested; low levels of cross-reactivity were not significantly different from the reactivity to GST-only, (d) SPF foal 2, which was initially experimentally infected with EHVl (foal 2a serum) and consequently reacted against GST-EHVl gG only , seroconverted after cross challenge with EHV4 (foal 2b serum) to become reactive against both GST-EHN4 gG and GST-EHVl gG. It was also noted that cross-challenge with EHN4 did not boost the response to GST-EHVl gG, indeed antibody to GST-EHN1 gG actually showed a 4-fold decrease, (e) The two post-EHVl abortion mare sera, which were obtained 5 weeks (abortion mare 1) and one year (abortion mare 2) after abortion, reacted strongly against both GST-EHVl gG and GST-EHV4 gG. (f) Exposure to different virus strains of EHV4 and EHNl did not affect the serological response to their respective GST-gG antigens, which is particularly relevant in the case of EHNl.849/89 which was isolated from abortion mare 2 and which is an intratypic variant EHNl .IB electropherotype As can be seen from the above description, examination of the supernatant of EHN4 infected cell cultures revealed the presence of two previously unidentified, secreted glycoproteins, one at 250K and the other at 63K. The 63K product was shown to unexpectedly elicit a type-specific antibody response in the horse, the first EHV4 or EHVl antigen known to produce such a response. There were two lines of evidence suggesting the 63K secreted product may be the EHV4 homologue of HSV gG: (a) gG homologues in PRV and HSV2 are also, at least in part, secreted into the cell culture medium and (b) gG homologues of other heφesviruses have proved to be relatively divergent glycoproteins and therefore perhaps more likely to produce a type-specific antibody response than other glycoproteins. These data led us to sequence the US region of the EHV4 genome adjacent to the internal repeat structure, the location of gG homologues in PRV, HSN1 and HSN2. The nucleotide sequence of four complete ORFs and one partial ORF were determined: ORF1 for which no homologue was found, ORF2 which showed similarity to HSN1 US2 which codes for an as yet unidentified protein, ORF3 which showed similarity to PRN US1 and HSN1 US3 genes which code in both cases for a protein kinase and ORF4 which showed most similarity to PRN US2 which codes for gX, the homologue of HSV gG. Although the predicted amino acid sequence of ORF4 showed only 28% and 16% identity PRN gX and HSN2 gG respectively, significantly greater identity was apparent toward the Ν-terminus including the conservation of 4 cysteine residues across the three glycoproteins. PRV gX and HSV2 gG were the only two sequences in the GenPept database to show significant similarity to ORF4. This gene was, therefore, considered to code for EHN4 gG. Evidence is accumulating that glycoprotein G homologues have some unusual features not found in other alphaheφesvirus glycoproteins. Perhaps the most striking of these is their considerable heterogeneity, particularly toward the C-terminus of the molecules. It is apparent that the genes have diverged widely both by point mutation and by the deletion and/or insertion of segments of DΝA. HSV1 gG in particular appears to have suffered a large internal deletion. Consequently the sizes of the predicted amino acids sequences are widely disparate compared to other alphaheφesvirus glycoprotein gene homologues; HSV1 gG comprises 238 amino acids, HSV2 gG 699, PRV gG (gX) 498, EHV4 gG 405, EHVl gG 411 and ILTN gG (gX) 298. The gG homologues of EHN4 and EHNl show only 58% amino acid identity; considerably less than the next most divergent of the sequenced EHV4/EHV1 glycoproteins, gC, which shows 79% identity and which possess both shared and unique epitopes It is perhaps not suφrising then that EHV4 gG and EHVl gG have proved to be the only EHN4/EHN1 antigens that are type-specific. Significantly, the epitopes responsible for eliciting a strong type-specific response in the natural host are localized to the apparently corresponding, C-terminal variable regions of EHN4 gG (amino acids 287-382) and EHNl gG (amino acids 288-350), regions which appear to have few constraints on either the number or -type of amino acid except perhaps that the amino acids in this region tend to be hydrophilic. Discontinuous epitopes, that are probably not formed in the E. coli expressed products, may be present on native gG molecules. Indeed another variable region comprising amino acids 32-57 of both EHN4 gG and EHNl gG, which does not appear to be antigenic in the E. coli expressed molecules, may comprises part of a discontinuous epitope. Such epitopes are largely type-specific since secreted ΕHV4 gG, as present in cell culture supernatant, reacts type-specifically with polyclonal horse sera in ELISA. Another feature of the gG homologues is that all, except HSV1 gG and EHVl gG, have been shown to be secreted, at least in part, into the growth medium. HSN1 gG does not appear to be secreted and this is probably due to a large internal deletion which results in the loss of the proteolytic cleavage site. In the case of EHVl gG, a secreted protein has not been detected in the infected cell culture supernatants from several different strains of EHVl using ELISA or Western blot analyses. This does not mean, however, that a secreted form of EHVl gG, does not exist. It is possible, as is predicted to be the case with EHV4 gG, that the proteolytic cleavage site is located within the C-terminal variable region, amino acids 288-350; a region which possesses a strong, perhaps the immunodominant, epitope(s). Proteolytic cleavage of EHNl gG may either destroy such an epitope(s) or leave the epitope(s) present in the virion associated species such that the secreted species does not possess any strong epitopes easily detectable in ELISA or Western blot. The complete lack of reactivity of an EHNl gG fusion protein expressing amino acids 1-310, which includes some of the variable region, lends some support to such a proposal. Application of glycoprotein G to a diagnostic test and vaccine development. The overall rational and methods for diagnostic testing and vaccine development used in the instant invention are well documented in the art and shall not be repeated in the instant specification. For example:- Australian Patent 591145, US Patent 5,041536, and WO 92/21751 disclose diagnostic kits, test methods and vaccination utilizing single virus types. Such methodology is generally applicable to the instant invention and the above documents are incoφorated by herein reference. WO 90/13652 and WO 90/13573 disclose diagnostic kits, test methods and vaccination utilizing dual virus types having a broad divergence. Such methodology is generally applicable to the instant invention and the above documents are herein incoφorated by reference. However, the instant invention differs from the specific disclosures above by allowing, for the first time, the diagnosis and selective treatment of two very closely related viruses which up until recently have remained virtually indistinguishable. It is evident since EHN4 gG and EHVl gG are type specific, that the genes coding for these glycoprotein could be deleted using recombinant DΝA techniques from vaccine strains of the two viruses such as that developed based on EHN4.405/76 and as described in U.S. Patent No. 5,084,271 although any strain of EHV4 or EHVl could be used. The deletion of the genes for gG would mean that a horse immunized with such vaccines would not make antibodies to the gGs, whereas a horse infected with wild type EHV4 and/or EHVl i.e., viruses containing the gene coding for gG, would make such antibodies. In this way horses immunized with a gG deletion mutant virus vaccine could be distinguished from horses infected or immunized with a gG containing virus. The data obtained since the priority date for EHV4 gG as presented herein confirms directly that EHNl gG is type specific, and that EHNl vaccine with a deleted gG gene would not produce antibodies to gG when administered to a horse, and that therefore a horse immunized with an EHVl gG deletion mutant virus can be distinguished from a horse infected with wild type EHNl i.e., a strain containing an intact gG gene. Accordingly not only does an immunological test where an enzyme linked immunosorbent assay (ELISA), in which EHV4 gG and EHVl gG are used as the antigens to distinguish horses that have been infected with either EHV4 or EHVl or both viruses, the same test in a somewhat modified format can be used to distinguish horses that have been immunized with EHV4 or EHVl or combined vaccines to both viruses in which the individual viruses i.e., EHV4 and EHVl, contain a deletion in the gG gene. Figures 11 and 12 suggest some of the many possible formats for the ELISA test kits that can be used. In Figure 12 it is shown that antibody pontained in horse serum is first added to the filter paper disc and allowed to react with the designated impregnated antigens. Following washing a second anti-species antibody, such as goat anti-horse IgG antibody, that is conjugated to an enzyme is added to the filter paper and allowed to react with any bound horse antibody. After further washing substrate to the enzyme is added. If EHV4 gG and/or EHNl gG antibody is present in the serum the EHN4 gG and/or EHVl gG spot will show a colour change, indicating the horse has been infected with EHV4 and/or EHVl or immunized with EHV4 and/or EHNl strains containing the gG gene. If the horse has been infected with both viruses, both gG spots will show a colour change and if the horse has been infected with neither virus neither spot will show a colour change. The test procedure and rationale as disclosed in the FIV test product, CITE , is incoφorated by reference. As illustrated in Figure 12, the test can equally be formatted in familiar 96-well microprocedure trays in which the gG antigens to EHN4 (well 1) and EHVl (well 2) are coated onto the bottom of alternate wells in the tray. Such a 96-well format, which includes appropriate control wells, such as whole EHV4 or EHVl virus (well 3) and uninfected cell lysate (well 4), is suitable for mass screening of serums from large horse populations. The test procedure and rationale as disclosed in the FTV test product, PETCHEK , is incoφorated herein by reference. With the development of vaccines based on the deletion of EHV4 gG and EHVl gG genes, in addition to having the two gG's as capture antigens, it is necessary for either the individual filter paper for testing individual horse serums or the 96-well or other formatted ELISAs to have a capture antigen to show that the horse has been immunized. Vaccines for the control of both EHN4 and EHVl are combined vaccines i.e. they contain a mixture of both viruses, the antigen used can be either whole virus e.g. EHV4 or EHVl. The whole viruses are known to contain many cross reactive epitopes. The invention also provides a basis for making recombinant DΝA vaccines by inserting into the gG gene location genes encoding important antigens from other equine pathogens such as those from equine influenza virus, equine arteritis virus, equine rhinovirus and equine adenovirus among others. It is also claimed that the gG insertion site could be useful for the insertion of other protein genes to be delivered to horses such as those encoding adjuvants. The insertion of such other genes into the gG gene could follow deletion of part of the gG gene to make a gG negative mutant virus. It is evident particularly from the seemingly large amount of EHV4 gG secreted into the medium of infected cultures that the gG gene possesses a strong promoter which is favourable for high level expression of foreign genes. Since modifications within the spirit and scope of the invention may be readily effected by persons skilled in the art, it is to be understood that the invention is not limited to the particular embodiment described, by way of example, herein above. TABLE 1. REACTIVITY OF INFECTED CELL CULTURE SUPERNATANTS IN ELISA ELISA Titres Serum EHV4/EHV1* mock S/N* EHV4 S/N EHVl S/N SPF foal pre bleed (pool) SPF foal 1 (post El) SPF foal 2a (post El) SPF foal 2b (post E1&E4) SPF foal 3 (post E4) post E4 serum No. 3 a Purified EHV4 or EHVl (10 μg/ml in coating buffer) was used to coat wells. Titres determined from a titration curve and expressed as logio of the reciprocal of the highest dilutio sera that gave an absorbance reading of at least twice the baseline reading. b Either mock, EHV4 (E4) or EHVl (El) infected cell culture supernatant (S/N) was used to wells (diluted 1:5 in coating buffer). Titres are expressed as the reciprocal of the highest dilutio sera than gave an absorbance of at least twice the baseline reading. UB TITUTE SHEE TABLE 2. Reactivity of EHV4 gG and EHVl gG GST-fusion proteins in ELISA a SPF foals 1 and 3 were immunised with inactivated virus before challenge with the homologous liv virus while all other horses received live virus via either experimental (SPF foal 2, post-E4 horses, pos EHV2 foal) or natural infection (abortion mares). The immunisation and experimental infectio protocols are described in references 23, 64 and the virus strains are described in references 56, 58. b Titers were determined from a titration curve and expressed as the reciprocal of the highest dilution o serum that gave an absorbance reading of at least twice the baseline reading. c Purified whole EHV4 or EHVl (10 μg/ml) was used to coat wells. d GST-fusion proteins prepared from E. coli transformed with parental pGEX (GST only), pEG4va (E4 gG aa287-382) and pEGlvar (El gG aa288-350) were used to coat wells at 0.5μg/ml. e Not determined " - _--■- SUBSTITUTE SHEET

Claims: The claims defining the invention are as follows:- 1. A substantially pure envelope glycoprotein of equine heφesvirus (EHV capable of distinguishing equine heφesvirus 4 (EHN4) from equine heφesvirus (EHNl). 2. An envelope glycoprotein according to claim 1 which is type-specific to EHV and EHNl. 3. An envelope glycoprotein according to claim 1 or 2 which belongs to th glycoprotein G set (gG). 4. An envelope glycoprotein according to any one of claims 1 to 3 derived fro EHN4 (EHV4 gG). 5. An envelope glycoprotein according to anyone of claims 1 to 3 derived fro EHVl (EHVl gG). 6. EHV4 gG according to claim 4 comprising a 405 amino acid sequence an corresponding to an unglycosylated Mr value of 44 kilodaltons. 7. EHVl gG according to claim 5 comprising a 411 amino acid sequence an corresponding to an unglycosylated Mr value of 45 kilodaltons. 8. EHV4 gG according to claim 6 comprising the following amino acid sequence: MLAVGATLCLLSFLTGATGRLAPDDLCYAEPRKTGPMPRSKPKHQPLLFEAPKVALTA ESKGCQLILLDPPIDMGYRLEDKINASIAWFFDFGNCRMPIAYREYYDCVGNAIPSPE TCDGYSFTLVKTEGWEFTIVNMSLLLQPGIYDSGSFIYSALLDMDVLTGRVILNVEN DTNYPCGMTHGLTADGNINVDETTHTTPHPRAVGCFPELINFDA ENVTFEEMGIPDP NSFLDDESDYPNTMDCYSWDLYTYPKSLKQAEGPQTLLIGAVGLRI AQAWKFVENET YSQHTRTYTRDAKEVDVTQPSPVQADSVLAKKRTSMKNNPIYSEGKPHAKPFSTIDSI HTEG KNNPVYSESLMLNVQHSDSITTGGVLHGLQDCDNQLKTVYICLALIGLAHVP or subsequences thereof capable of eliciting a type-specific response including naturally occurring derivatives, variants, genetically engineered derivatives, glycosylated forms of the proteins or synthetically made derivatives. 9. A substantially pure nucleotide sequence corresponding to the coding region of EHV4 gG according to claim 8 comprising the following nucleotide sequence: - ATTTGGGGTGGAGACGGCGTGGGCCGATACTGTATAAAGTTGTACTACTTACCAGCCC AGTCAGTGTGCTGTAGTGCCACCACCTGTAAAGCTGTGATAAGCTGCAGGCATATGTT GGCTGTGGGAGCAACTCTGTGTTTACTGAGTTTCCTAACTGGCGCTACTGGACGGCTA GCTCCTGACGACCTCTGCTATGCAGAACCCCGCAAAACCGGTCCCATGCCCCGCTCAA AACCTAAACACCAACCCCTACTATTTGAAGCCCCAAAGGTTGCTCTTACGGCAGAGTC AAAGGGTTGTCAACTAATATTGTTAGACCCTCCAATAGACATGGGCTATCGCTTAGAG GACAAGATAAACGCTTCCATTGCTTGGTTTTTTGACTTTGGTAATTGTCGAATGCCCA TCGCATACAGAGAGTACTATGATTGCGTTGGCAACGCAATCCCATCTCCAGAAACATG TGATGGTTACTCATTTACACTTGTTAAAACAGAGGGTGTAGTTGAGTTTACCATCGTA AACATGAGCTTACTGTTGCAGCCTGGAATATACGACAGTGGAAGTTTTATATACAGCG CCCTTCTAGATATGGATGTATTGACTGGACGCGTAATTTTGAACGTGGAGAACGACAC TAACTATCCATGCGGAATGACTCACGGCCTCACTGCGGATGGCAACATCAACGTAGAT GAAACCACGCACACAACCCCACATCCACGTGCTGTCGGGTGTTTTCCAGAACTCATTA SUBSTITUTESHEET ACTTCGATGCATGGGAAAACGTTACATTCGAAGAAATGGGGATACCAGACCCAAACTC ATTTCTTGATGATGAGAGTGATTACCCGAATACAATGGACTGTTACTCGTGGGATTTA TACACATATCCCAAAAGCCTGAAGCAGGCAGAGGGGCCCCAAACCTTGTTAATAGGTG CAGTTGGACTCAGAATACTCGCGCAAGCATGGAAGTTTGTTGAAAATGAAACCTACAG CCAGCATACACGTACGTACACACGTGATGCTAAGGAAGTTGATGTTACACAGCCAAGT CCTGTACAGGCTGATTCTGTCCTCGCCAAGAAACGCACATCTATGAAGAATAACCCTA TTTATTCAGAGGGGAAGCCTCATGCTAAACCGTTCAGCACGATAGACAGCATCCACAC GGAAGGGATGAAGAATAACCCTGTTTATTCAGAGAGCCTCATGCTAAACGTCCAGCAC AGTGACAGCATCACCACCGGGGGTGTGTTGCATGGCCTCCAAGACTGCGACAACCAGC TCAAAACTGTGTATATTTGCCTAGCTCTTATTGGACTCGCACATGTGCCATGATAGGA CTAATAGTTTACATTTTTGTGCTAAGGTCAAAAATATCTTCCCACAATTTATCGCGCT CACAAAATGTAAAACATAGAAACTATCATCGACTTGAGTACGTTGCATAATACATGTC AAAATAAAAGTTAAAAATTAAACATTGTTGTCTGTAATAACTGAGTGTGGTTTTAAAA AATACTAAATCGCGGCAATGTT or degeneracy equivalents or subsequences thereof coding for amino acid sequences or epitopes capable of eliciting a type-specific response. 10. EHVl gG according to claim 7 comprising the following amino acid sequence:- MLTVLAALSLLSL TSATGRLAPDELCYAEPRRTGSPPNTQPERPPVIFEPPTIAIKA ΞSKGCELILLDPPIDVSYRREDKVNASIA FFDFGACRMPIAYREYYGCIGNAVPSPE TCDAYSFTLIRTEGIVEFTIVNMSLLFQPGIYDSGNFIYSVLLDYHIFTGRVTLEVEK DTNYPCGMIHGLTAYGNINVDETMDNASPHPRAVGCFPEPIDNEA ANVTFTELGIPD PNSFLDDEGDYPNISDCHS ESYTYPNTLRQATGPQTLLVGAVGLRILAQA KFVGDE TYDTIRAEAKNLETHVPSSAAESSLENQSTQEESNSPEVAHLRSVNSDDSTHTGGASN GIQDCDSQLKTVYACLALIGLGTCAMIGLIVYICVLRSKLSSRNFSRAQNVKHRNYQR LEYVA or subsequences thereof capable of eliciting a type-specific response including naturally occurring derivatives, variants, genetically engineered derivatives, glycosylated forms of the proteins or synthetically made derivatives. 11. An EHV4 epitope capable of eliciting a type-specific response contained within EHV4 gG amino acids 287 - 382 (as herein defined in Fig 5A). 12. An EHV4 epitope according to claim 11 having the following amino acid sequence: ENETYSQHTRTYTRDAKEVDVTQPSPVQADSVLAKKRTSMKNNPIYSEGKPHAKPFST IDSIHTEGMKNNPVYSESLMLNVQHSDSITTGGVLHGL or subsequences thereof capable of eliciting a type-specific response including naturally occurring derivatives, variants, genetically engineered derivatives, glycosylated forms of the proteins or synthetically made derivatives. 13. An EHV4 epitope capable of eliciting a type-specific response encompassed by the following amino acid sequence KTGPMPRSKPKHQPLLFEAPKVALT or subsequences thereof capable of eliciting a type-specific response including naturally occurring derivatives, variants, genetically engineered derivatives, glycosylated forms of the proteins or synthetically made derivatives. SUBSTITUTE SHEET 14. An EHV4 discontinuous epitope characterized by a discontinuous combination of the epitopes according to claim 12 and 13 or derivatives of these 2 regions, either alone or together, with other regions of the EHV4 gG molecule. 15. Plasmid vector pEG4var (as hereinbefore defined). 16. Host cells transformed with pEG4var. 17. An EHVl epitope capable of eliciting a type-specific response contained within EHVl gG amino acids 288 - 350 (as herein defined in Fig 5A). 18. An EHVl epitope according to claim 17 having the following amino acid sequence:- GDETYDTIRAEAKNLETHVPSSAAESSLENQSTQEESNSPEVAHLRSVNSDDSTHTGG ASNGI or subsequences thereof capable of eliciting a type-specific response including naturally occurring derivatives, variants, genetically engineered derivatives, glycosylated forms of the proteins or synthetically made derivatives. 19. An EHVl epitope capable of eliciting a type-specific response encompassed by the following amino acid sequence. RTGSPPNTQPERPPVIFEPPTIAIK SUBSTITUTE SHEET or subsequences thereof capable of eliciting a type-specific response including naturally occurring derivatives, variants, genetically engineered derivatives, glycosylated forms of the proteins or synthetically made derivatives. 20. An EHVl discontinuous epitope characterized by a discontinuous combination of the epitopes according to claims 18 and 19 or derivatives of these 2 regions, either alone or together, with other regions of the EHVl gG molecule. 21. A plasmid vector pEGlvar (as hereinbefore defined). 22. Host cells transformed with pEGlvar. 23. Vaccine for selective immunization of horses against EHV4 and/or EHVl. 24. Vaccine according to claim 23 which is a deletion mutant vaccine characterized by the deletion of EHV4 gG amino acids 287 - 382 or subsequences thereof capable of eliciting a type-specific response. 25. Vaccine according to claim 23 which is a deletion mutant vaccine characterized by the deletion of EHVl gG amino acids 288 - 350 or subsequences thereof or amino acids located elsewhere in the gG molecule that are either directly or indirectly capable of eliciting a type-specific SUBSTITUTE SHEET response. 26. A vaccine composition comprising an immunogenic amount of the EHV4 epitope according to any one of claims 11 to 14 in a physiologically acceptable vehicle. 27. A vaccine composition comprising an immunogenic amount of the EHVl epitope according to any one of claims 17 to 20 in a physiologically acceptable vehicle. 28. Vaccine according to claim 23 which is an insertion mutant vaccine comprising a mutant of EHV4 or EHVl containing a heterologous gene coding for equine inf luenza virus haemagglutinin antigens or other equine virus antigens including equine in luenza neurimidase or nucleoprotein antigens or derivatives thereof inserted downstream of the gG promotor by recombinant DNA techniques. 29. Vaccine according to claim 23 which is an insertion mutant vaccine comprising a mutant of EHV4 or EHVl containing a heterologous gene coding for any one or a combination of equine arteritis virus, equine rhinovirus and equine adenovirus inserted downstream of the gG promotor by recombinant DNA techniques. SUBSTITUTE SHEET 30. A vaccine for selective immunization of horses against EHV4 and/or EHVl characterized by the substitution of any one of the type-specific envelope glycoproteins according to claim 3 with a foreign gene or genes and further characterized by the substitution of the gG promotor with a oreign promotor. 31. An immunological test kit for determining the EHV4 and 1 status of an horse characterized by capture antigens in the form of envelope glycoproteins of equine heφesvirus capable of distinguishing horses infected with EHV4 and EHVl. 32. An immunological test kit according to claim 31 wherein the capture antigens are those defined in any one of claims 2 to 8, 10 to 14 and 17 to 20. 33. An immunological test method for determining the EHV status of a horse comprising at least the following steps: - a) Antibody contained in horse serum is added to a filter paper disc and allowed to react with EHV4 gG or EHVl gG capture antigens; b) Following washing a second anti-species antibody conjugated to an enzyme marker is added to the filter paper and allowed to react with any specifically bound horse antibody; c) After a further washing, an enzyme substrate capable of generating a signal is added. SUBSTITUTE SHEET 34. An immunological test method according to claim 32 for detection of the presence of wild type EHV4 characterized by testing for the presence of EHV4 gG. 35. An immunological test method according to claim 32 for detection of the presence of wild type EHVl characterized by testing for the presence of EHVl gG. 36. An immunological test method according to claim 32 for determining whether a horse has been vaccinated against EHV4 by testing for the presence of EHV4 and the absence of EHV4 gG. 37. An immunological test method according to claim 32 for determining whether a horse has been vaccinated against EHVl by testing for the presence of EHVl and the absence of EHVl gG. 38. An immunological test method according to claim 32 for determining when a horse has been neither infected with nor vaccinated against EHV4 by testing for the absence of EHV4 gG antibodies. 39. An immunological test method according to claim 32 for determining when a horse has been neither infected with nor vaccinated against EHVl by testing for the absence of EHVl gG antibodies. SUBSTITUTE SHEET 40. Antibodies to any one of EHV epitopes as defined in claims 2 to 8, 10 to 14 and 17 to 20. 41. Antibodies according to claim 40 which are monoclonal or polyclonal. 42. Hybridization nucleic acid probes specific for EHVl or EHV4. 43. Hybridization probes according to claim 42 comprising a nucleotide sequence complimentary to the nucleotide sequence coding for the amino acid sequence of any one of the glycoproteins defined in claims 2 to 8, 10 to 14 or 17 to 20 or derivatives thereof.

Inventors: CRABB BRENDAN SCOTT, STUDDERT MICHAEL JUSTIN, CRABB, BRENDAN, SCOTT, STUDDERT, MICHAEL, JUSTIN
Applicants: CRABB BRENDAN SCOTT, STUDDERT MICHAEL JUSTIN, UNIV MELBOURNE, THE UNIVERSITY OF MELBOURNE
Application year: 1993
Main classification: C07K7
IPC codes: A61K38, A61K39, A61P31, C07K14, C12N7, C12N15