Abstract:
The present invention relates to a recombinant fusion interferon for animals, a pharmaceutical composition thereof, and the use of the recombinant fusion interferon. The recombinant fusion interferon is represented by formula (I) or formula (II),
 
(Porcine interferon)-(Linker) n -(Porcine immunoglobulin Fc fragment)   (I)
 
(Porcine immunoglobulin Fc fragment)-(Linker) n -(Porcine Interferon)   (II)
 
wherein n is 0 or a positive integer between 1 to 10, the recombinant fusion IFN specifically binds an antibody that specifically binds porcine interferon and an antibody that specifically binds porcine immunoglobulin Fc fragment.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 13/557,139, filed Jul. 24, 2012, entitled “RECOMBINANT FUSION INTERFERON FOR ANIMALS” by Tsun-Yung Kuo, Chung-Chin Wu, and Han-Ting Chen. The disclosure of the above identified co-pending application is incorporated herein by reference in its entirety. 
     Some references, if any, which may include patents, patent applications and various publications, may be cited and discussed in the description of this invention. The citation and/or discussion of such references, if any, is provided merely to clarify the description of the present invention and is not an admission that any such reference is “prior art” to the invention described herein. All references listed, cited and/or discussed in this specification are incorporated herein by reference in their entireties and to the same extent as if each reference was individually incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a recombinant fusion interferon for animals, particularly to a recombinant fusion interferon having antiviral activities against animal viruses. 
     BACKGROUND OF THE INVENTION 
     Interferon (IFN) is initially discovered in 1957 by Alick Isaacs and Jean Lindenmann during research of influenza virus. After infected by virus, the host cells immediately secrete a cytokine to induce other cells nearby to produce antiviral proteins to interfere with viral replication. This cytokine is later named IFN. Since the first discovery of IFN, three types of IFN have been identified—type I IFN (IFN-α and IFN-β), type II IFN (IFN-γ), and type III IFN (IFN-λ). The antiviral effects of IFN are mainly provided by type I IFN (IFN-α and IFN-β). In addition to antiviral activities, IFN has anti-tumor activity, and can induce cell differentiation and modulate immune response. 
     So far, the majority of commercial IFN is used for the treatment of human diseases, such as human hepatitis B, human hepatitis C, Kaposi&#39;s sarcoma (KS), and malignant melanoma. 
     Without an effective vaccine for preventing an animal virus, an infected animal of the virus can only be treated with supportive therapy. However, supportive therapy is usually ineffective, and therefore the infection of animal virus may cause great economic losses in livestock husbandry. 
     Therefore, it is important to develop IFN having antiviral activities against animal viruses. 
     SUMMARY OF THE INVENTION 
     The first aspect of the present invention relates to a recombinant fusion IFN for animals. IFN possesses a short serum half-life (about 2 to 8 hours) due to its small molecular size. The present invention provides a stably recombinant fusion IFN for animals in which a porcine IFN is fused with a porcine immunoglobulin Fc fragment (IgG Fc) possessing a long serum half-life. The porcine IgG Fc is fused with the N-terminus or the C-terminus of the porcine IFN. The porcine IFN and the porcine IgG Fc can be further joined by a peptide linker. Therefore, the recombinant fusion IFN of the present invention is represented by formula (I) or formula (II)
 
(Porcine interferon)-(Linker) n -(Porcine immunoglobulin Fc fragment)   (I)
 
(Porcine immunoglobulin Fc fragment)-(Linker) n -(Porcine Interferon)   (II)
 
where:
 
     the porcine interferon has at least 85%, preferably 90%, even more preferably 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% sequence identity with the sequences of SEQ ID NOs: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, and 17; 
     the porcine immunoglobulin Fc fragment has at least 85%, preferably 90%, even more preferably 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% sequence identity with the sequences of SEQ ID NOs: 18, 19, 20, 21, and 22; 
     the linker has at least one glycine, and the linker has a sequence including, but not limited to, glycine-glycine, glycine-serine, the sequences of SEQ ID NOs: 23, 24, 25, 26, 27, 28, 29, 30, 31, and 32; 
     n is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10; and 
     the recombinant fusion IFN specifically binds an antibody that specifically binds porcine interferon and an antibody that specifically binds porcine immunoglobulin Fc fragment. 
     In one embodiment, the porcine IFN encodes an amino acid sequence of SEQ ID NOs: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, or 17. The porcine IgG Fc encodes an amino acid sequence of SEQ ID NOs: 18, 19, 20, 21, or 22. The linker encodes an amino acid sequence of SEQ ID NOs: 23, 24, 25, 26, 27, 28, 29, 30, 31, or 32. In one example, the recombinant fusion IFN has a sequence from any one of SEQ ID NOs: 41-51. Each of the SEQ ID NOs: 41-51 includes a SEQ IN NO: 2, any one of the SEQ ID NOs: 23-32, and a SEQ ID NO: 22. 
     In one preferred embodiment, the porcine IFN encodes an amino acid sequence of SEQ ID NO: 1, the porcine IgG Fc encodes an amino acid sequence of SEQ ID NO: 22, and the linker encodes an amino acid sequence of SEQ ID NO: 23. 
     In another preferred embodiment, the porcine IFN encodes an amino acid sequence of SEQ ID NO: 2, the porcine IgG Fc encodes an amino acid sequence of SEQ ID NO: 18, and the linker encodes an amino acid sequence of SEQ ID NO: 23. 
     The recombinant fusion IFN of the present invention is made by gene cloning technology. A DNA sequence encoding a porcine IFN and a DNA sequence encoding a porcine IgG Fc are cloned into an expression vector to obtain a polynucleotide encoding the recombinant fusion IFN. The vector containing the polynucleotide encoding the recombinant fusion IFN is then introduced to a host cell where the recombinant fusion IFN can be expressed. An additional DNA sequence encoding a peptide linker having glycine and serine residues can be further cloned into the expression vector to join the DNA sequence encoding a porcine IFN and the DNA sequence encoding a porcine IgG Fc. 
     The expression vector can be a prokaryotic expression vector or a eukaryotic expression vector. The prokaryotic expression vector includes, but is not limited to, pET, pGEX, and pDEST expression vectors. The eukaryotic expression vector includes, but is not limited to, pSecTag, pcDNA3, pCMV-Script, pCI, and pSV40b expression vectors. 
     The host cell can be a prokaryotic cell, such as bacteria, or a eukaryotic cell, such as yeast, insect cells, plant cells, and mammalian cells. An example of bacteria includes, but not limited to,  Escherichia coli  ( E. coli .). An example of mammalian cells that can be used to express the recombinant fusion IFN of the present invention includes, but are not limited to, 3T3 cells, Chinese hamster ovary cells (CHO cells), baby hamster kidney cells (BHK cells), human cervical cancer cells (such as Hela cells), and human liver carcinoma cells (such as HepG2 cells). 
     The second aspect of the present invention relates to a composition comprising the recombinant fusion IFN of the present invention and a pharmaceutically acceptable excipient. 
     The excipient may be pharmaceutically acceptable organic or inorganic carrier substances suitable for parenteral, enteral or intranasal application which do not deleteriously react with the active compounds and are not deleterious to the recipient thereof. Suitable excipients include, but are not limited to, water, salt solutions, vegetable oils, polyethylene glycols, gelatin, lactose, amylose, magnesium stearate, talc, silicic acid, viscous paraffin, fatty acid monoglycerides and diglycerides, petroethral fatty acid esters, hydroxymethyl-cellulose, polyvinylpyrrolidone, etc. In one embodiment, the excipient is phosphate buffer solution (PBS). 
     The third aspect of the present invention relates to a method for treating or inhibiting virus infection in an animal. In one embodiment, the method comprises administering a composition comprising the recombinant fusion IFN of the present invention to an animal. The virus may be an animal DNA virus or an animal RNA virus. The animal virus includes, but is not limited to, pseudorabies virus (PRV), porcine reproductive and respiratory syndrome virus (PRRSV), parvovirus, Transmissible gastroenteritis coronavirus (TGEV), Japanese encephalitis virus (JEV), Rotavirus, Porcine circovirus type 2 (PCV2), foot and mouth disease virus (FMDV), hog cholera virus (HCV), African swine fever virus, swinepox virus, porcine cytomegalovirus, porcine epidemic diarrhea virus, swine vesicular disease virus, porcine teschovirus, procine astrovirus. The animal may be an animal infected with an animal virus or an animal not infected with an animal virus. In another embodiment, the composition further comprises a pharmaceutically acceptable excipient. 
     These and other aspects of the present invention will become apparent from the following description of the preferred embodiment taken in conjunction with the following drawings, although variations and modifications therein may be effected without departing from the spirit and scope of the novel concepts of the disclosure. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention is more particularly described in the following examples that are intended as illustrative only since numerous modifications and variations therein will be apparent to those skilled in the art. Various embodiments of the invention are now described in detail. Referring to the drawings, like numbers indicate like components throughout the views. 
     As used in the description herein and throughout the claims that follow, the meaning of “a”, “an”, and “the” includes plural reference unless the context clearly dictates otherwise. Moreover, titles or subtitles may be used in the specification for the convenience of a reader, which shall have no influence on the scope of the present invention. 
     The terms “treat,” “treating,” “treatment,” and the like are used herein to refer to prevention or partially preventing a disease, symptom, or condition and/or a partial or complete cure or relief of a disease, condition, symptom, or adverse effect attributed to the disease. Thus, the terms “treat,” “treating,” “treatment,” and the like refer to both prophylactic and therapeutic treatment regimes. 
     The terms “inhibit,” “inhibiting,” “inhibition,” and the like are used herein to refer to a reduction or decrease in a quality or quantity, compared to a baseline. For example, in the context of the present invention, inhibition of viral replication refers to a decrease in viral replication as compared to baseline. Similarly, inhibiting virus infection refers to a decrease in virus infection as compared to baseline. 
     The term “antiviral activity” is used herein to refer to that the IFN can inhibit or interfere the biological activity of virus. 
     The term “biological activity of virus” is used herein to refer to virus infection, replication, and the like. 
     The meaning of the technical and scientific terms as described herein can be clearly understood by a person of ordinary skill in the art. 
     EXAMPLE 1 
     Molecular Cloning of Porcine Interferon 
     Peripheral blood mononuclear cells (PBMCs) were firstly isolated from blood of a pig (L×Y-D strain). A total RNA was isolated from the PBMCs by the guanidine thiocyanate (GTC) method and then was used in a reverse transcription polymerase chain reaction (RT-PCR) to generate complementary DNA (cDNA). The cDNA was then used as DNA template to amplify porcine interferon genes by polymerase chain reaction (PCR). A forward primer and a reverse primer were designed to amplify the porcine interferon nucleotide sequence. The forward primer in this example has a HindIII cleavage site, and the reverse primer in this example has an Xho I cleavage site. The primers for cloning porcine interferon genes are the following: 
     
       
         
               
               
             
           
               
                   
                 Forward primer (IFN-F1): 
               
               
                   
                 (SEQ ID NO: 34) 
               
               
                   
                 5′-CCC   AAGCTT   ATGGCCCCAACCTCAGCC-3′ 
               
               
                   
                        HindIII 
               
               
                   
               
               
                   
                 Reverse primer (IFN-R1): 
               
               
                   
                 (SEQ ID NO: 35) 
               
               
                   
                 5′-CCG          CAGGTTTCTGGAGGAAGA-3′ 
               
               
                   
                        XhoI 
               
             
          
         
       
     
     The PCR was carried out as follows: inactivation of cDNA at 95° C. for 5 minutes, amplification of porcine interferon genes by Taq polymerase with 30 cycles of 95° C. for 1 minute, 55° C. for 30 seconds, 72° C. for 30 seconds, and final extension at 72° C. for 5 minutes. 
     The PCR products were then constructed into a pET20b expression vector with the restriction enzyme cutting sites, Hind III and Xho I. Plasmids containing the PCR products were transformed into host cells ( E. coli ). Transformants were selected and sequenced, and then the DNA sequences of the PCR products were translated into amino acid sequences. Seventeen (17) different amino acid sequences of porcine interferon were cloned, and their sequence are shown as SEQ ID NOs: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, and 17. 
     EXAMPLE 2 
     Synthesis of Porcine Recombinant Fusion Interferon 
     The porcine interferon genes cloned in Example 1 were used to synthesize the porcine recombinant fusion interferon of the present invention. DNA sequences encoding the recombinant fusion interferon were synthesized by a DNA synthesizer. The recombinant fusion interferon is represented by formula (I) or formula (II)
 
(Porcine interferon)-(Linker) n -(Porcine immunoglobulin Fc fragment)   (I)
 
(Porcine immunoglobulin Fc fragment)-(Linker) n -(Porcine Interferon)   (II)
 
where:
 
     the porcine interferon encodes an amino acid sequence of SEQ ID NOs: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, or 17; 
     the porcine immunoglobulin Fc fragment encodes an amino acid sequence of SEQ ID NOs: 18, 19, 20, 21, and 22; 
     the linker has a sequence of glycine-glycine, glycine-serine, or the sequences of SEQ ID NOs: 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, or 33; and 
     n is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. 
     An EcoRV site at the 5′ end and a HindIII site at the 3′ end were added to the DNA sequences of the porcine recombinant fusion interferon when the DNA sequences were synthesized. The synthesized DNA sequences were then constructed into a pcDNA3 expression vector with the restriction enzyme cutting sites, EcoRV and Hind III. Plasmids containing the synthesized DNA sequences were transformed into host cells ( E. coli ). 
     The pcDNA3 expression vectors containing the synthesized DNA sequences were then transfected into CHO cells using Lipofectamine (Invitrogen) according to the manufacturer&#39;s instructions. The transfected CHO cells were then cultivated at 37° C., 5% CO 2  in F12 medium containing 10% fetal bovine serum (FBS) for 48 hours. 
     After that, the transfected CHO cells were cultivated at 37° C., 5% CO 2  in F12 medium with 10% FBS, 100 units/ml penicillin, 100 units/ml streptomycin, and 100-700 μg/ml Zeocin to select cells comprising the porcine recombinant fusion IFN gene. The selective medium was replenished every 3 to 4 days until 10 to 20% of cells survived. The surviving cells were cultivated in F12 medium with 10% FBS until the cells grew to near confluence. Expression of the porcine recombinant fusion IFN from the selective cells was then detected by Western blot with proper antibodies. 
     Sample cells were cultivated in F-12 medium with 10% FBS for 72 hours, and then the supernatant was collected and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). For protein immunoblotting, following electrophoresis, proteins were transferred to a PVDF membrane. The resulting membrane was blocked with 5% skim milk in TBST (10 mM Tris-HCl pH 8.0, 150 mM NaCl, 0.3% Tween 20) at 4° C. for 16 to 24 hours to prevent non-specific binding of proteins and then washed 3 times with TBST. The membrane was then incubated with mouse anti IFNα monoclonal antibody (SANTA CRUZ) (1:500 dilution in TBST containing 0.5% skin milk) at room temperature for 1 hour. The blots were then washed 6 times with TBST and incubated with alkaline phosphatase (AP) conjugated goat anti-mouse IgG monoclonal antibody (1:2000 dilution in TBST containing 0.5% skin milk) at room temperature for 1 hour. The blots were then washed 6 times with TBST. The bands were detected using nitro blue tetrazolium (NBT)/5-bromo-4-chloro-3-indolyl-phosphate (BCIP) substrate for 5 minutes and then washed with water to stop the reaction. In addition, the porcine recombinant fusion IFN (P IFN-Fc) was also detected using alkaline phosphatase (AP) conjugated goat anti-porcine IgG antibody (KPL) and using alkaline phosphatase (AP) conjugated mouse anti 6× His monoclonal antibody (invitrogen). 
     Protein expressed in CHO cells that were transfected with a DNA sequence of the porcine recombinant fusion IFN is confirmed by Western blots. The porcine recombinant fusion IFN detected has the following formula: (Porcine interferon)-(Linker) 1 -(Porcine immunoglobulin Fc fragment), where the porcine interferon encodes an amino acid sequence of SEQ ID NO: 1, the porcine immunoglobulin Fc fragment encodes an amino acid sequence of SEQ ID NO: 22, and the linker encodes an amino acid sequence of SEQ ID NO: 23. The porcine recombinant fusion IFN was detected by mouse anti IFNα monoclonal antibody, mouse anti 6× His monoclonal antibody, and goat anti-porcine IgG antibody. The results show that transfected CHO cells secrete the porcine recombinant fusion IFN (SEQ ID NO: 1-SEQ ID NO: 23-SEQ ID NO: 22). 
     Protein expressed in CHO cells that were transfected with another DNA sequence of the porcine recombinant fusion IFN is confirmed by Western blots. The porcine recombinant fusion IFN detected has the following formula: (Porcine interferon)-(Linker) 1 -(Porcine immunoglobulin Fc fragment), where the porcine interferon encodes an amino acid sequence of SEQ ID NO: 2, the porcine immunoglobulin Fc fragment encodes an amino acid sequence of SEQ ID NO: 22, and the linker encodes an amino acid sequence of SEQ ID NO: 33. The porcine recombinant fusion IFN was detected by mouse anti IFNα monoclonal antibody and goat anti-porcine IgG antibody. The results show that transfected CHO cells secrete the porcine recombinant fusion IFN of SEQ ID NO: 51 (SEQ ID NO: 2-SEQ ID NO: 33-SEQ ID NO: 22). 
     EXAMPLE 3 
     Production of Porcine Recombinant Fusion IFN 
     CHO cells transfected with the porcine recombinant fusion IFN (SEQ ID No: 1-SEQ ID No: 23-SEQ ID No: 22) was seeded at a density of 2×10 6  cells in a 25 cm 2  cell culture flask and cultivated in F12 medium with 10% FBS, 100 units/ml penicillin, and 100 units/ml streptomycin for 24 hours. The medium was then removed. The cells were washed with PBS and then cultivated in F12 medium with 1% FBS, 100 units/ml penicillin, and 100 units/ml streptomycin. Supernatant was collected and fresh medium containing 1% FBS, penicillin, and streptomycin was added every 72 hours. The supernatant containing the porcine recombinant fusion IFN was centrifuged (1,000 rpm) for 10 minutes to remove cells and cell debris. 
     EXAMPLE 4 
     Analysis of Antiviral Activities Against PRRSV of the Porcine Recombinant Fusion IFN 
     The porcine recombinant fusion IFN obtained in Example 3 was diluted serially (10, 20, 40, 80, 160, 320, 640, 1280, and 2560-folds) with minimum essential media (MEM medium) containing 1% FBS, 100 units/ml penicillin, and 100 units/ml streptomycin. MARC-145 cells were seeded at a density of 1.5×10 4  cells/well in 96-well cell culture plates and cultivated at 37° C., 5% CO 2  for 16 to 24 hours. After the culture medium was removed, the cells were treated with the diluted porcine recombinant fusion IFN or porcine interferon having an amino acid sequence of SEQ ID NO: 1 (100 μl/well, n=4), and then cultivated at 37° C., 5% CO 2  for 24 hours. After the diluted samples were removed, the cells were infected with PRRS virus (100 TCID 50 /100 μl) and then cultivated at 37° C., 5% CO 2  for 4-5 days. Then cells were used to evaluate the antiviral activity of the porcine recombinant fusion IFN by MTT assay. 
     Cell suspension was removed, and the cells were washed twice with PBS and then fixed on the plate with 80% acetone (−20° C., 100 μl/well) at 4° C. for 30 minutes. After acetone was removed, the cells were washed 3 times with PBS and stained with 1% methylrosaniline chloride for 20 minutes. After that, the cells were washed 5 times with distilled water, and then 100% ethanol was added to dissolve methylrosaniline chloride. 10 minutes later, the absorbance of the signals was read using an ELISA reader set at 550 nm. Concentration of the porcine recombinant fusion IFN (P IFN-Fc) was calculated by the following formulas. 
                         OD   ⁢           ⁢   maximum     +     OD   ⁢           ⁢   minimum       2     =     OD   ⁢           ⁢   50   ⁢   %             Formula   ⁢           ⁢   1               
where OD maximum is absorbancy of uninfected cell monolayers treated or untreated with IFN (protection 100%), and OD minimum is absorbancy of the infected non-protected cell monolayer (protection zero).
 
                     IFN   ⁢           ⁢     titer   ⁡     (     U   ⁢           ⁢     ml     -   1         )         =       T   n     +     ⌈       (       T     n   +   1       -     T   n       )     ×       (       OD   n     -     OD   ⁢           ⁢   50   ⁢   %       )       (       OD   n     -     OD     n   +   1         )         ]               Formula   ⁢           ⁢   2               
where T n  is reciprocal of the IFN dilution corresponding to OD immediately higher than OD50%, T n+1  is reciprocal of the IFN dilution corresponding to OD immediately lower than the OD50%, OD n  is the absorbancy values immediately higher than OD50%, and OD n+1  is the absorbancy values immediately lower than OD50%.
 
     Table 1 show the results of the assays of antiviral activity against PRRSV of the porcine recombinant fusion IFN and the porcine IFN. The results show that the porcine recombinant fusion IFN possesses a higher antiviral activity against PRRSV than the porcine IFN. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Comparison of antiviral activities against PRRSV of the 
               
               
                 porcine recombinant fusion IFN and the porcine IFN. 
               
             
          
           
               
                   
                   
                 Antiviral Activities Against 
               
               
                   
                 Treatment 
                 PRRSV (IU/ml) 
               
               
                   
                   
               
               
                   
                 Porcine recombinant fusion IFN 
                 3147 
               
               
                   
                 Porcine IFN 
                 1500 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE 5 
     Analysis of Antiviral Activities Against PRV of the Porcine Recombinant Fusion IFN 
     The porcine recombinant fusion IFN obtained in Example 3 was diluted serially (10, 20, 40, 80, 160, 320, 640, 1280, and 2560-folds) with minimum essential media (MEM medium) containing 1% FBS, 100 units/ml penicillin, and 100 units/ml streptomycin. ST cells were cultivated at a density of 1.5×10 4  cells/well in 96-well cell culture plates at 37° C., 5% CO 2  for 16 to 24 hours. After the culture medium was removed, the cells were treated with the porcine recombinant fusion IFN obtained in Example 3 or the porcine IFN encoding an amino acid sequence of SEQ ID NO. 1 for 16 to 24 hours. After the two types of IFN were removed, the cells were infected with PR virus (1 TCID 50 /100 μl) and then cultivated at 37° C., 5% CO 2  for 4 to 5 days. Then cell viabilities were analyzed by MTT method, which is described in Example 4. 
     Table 2 and show the results of the assays of antiviral activity against PRV of the porcine recombinant fusion IFN and the porcine IFN. The results show that the porcine recombinant fusion IFN possesses a higher antiviral activity against PRV than the porcine IFN. 
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Comparison of antiviral activities against PRV of the 
               
               
                 porcine recombinant fusion IFN and the porcine IFN. 
               
             
          
           
               
                   
                   
                 Antiviral Activities Against 
               
               
                   
                 Treatment 
                 PRRSV (IU/ml) 
               
               
                   
                   
               
             
          
           
               
                   
                 Porcine recombinant fusion IFN 
                 4000 
               
               
                   
                 Porcine IFN 
                 960 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE 6 
     Analysis of Antiviral Activities Against Porcine Parvovirus of the Porcine Recombinant Fusion IFN 
     The porcine recombinant fusion IFN obtained in Example 3 was diluted serially (10, 20, 40, 80, 160, 320, 640, 1280, and 2560-folds) with minimum essential media (MEM medium) containing 1% FBS, 100 units/ml penicillin, and 100 units/ml streptomycin. ST cells were cultivated at a density of 1×10 4  cells/well in 96-well cell culture plates at 37° C., 5% CO 2  for 24 hours. After the culture medium was removed, the cells were treated with the diluted porcine recombinant fusion IFN for 24 hours. After the two types of IFN were removed, the cells were infected with porcine parvovirus (100 TCID 50 /100 μl) and then cultivated at 37° C., 5% CO 2  for 5 days. Then cell viabilities were analyzed by MTT method, which is described in Example 4. 
     The antiviral activities against porcine parvovirus of the porcine recombinant fusion IFN obtained in Example 3 is 3101 IU/ml. The result shows that the porcine recombinant fusion IFN possesses an antiviral activity against PRV. 
     Based on the results of the Examples above, the recombinant fusion IFN of the present invention possesses higher antiviral activities against both RNA virus and DNA virus than a porcine IFN. 
     The foregoing description of the exemplary embodiments of the invention has been presented only for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in light of the above teaching. 
     The embodiments are chosen and described in order to explain the principles of the invention and their practical application so as to activate others skilled in the art to utilize the invention and various embodiments and with various modifications as are suited to the particular use contemplated. Alternative embodiments will become apparent to those skilled in the art to which the present invention pertains without departing from its spirit and scope. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description and the exemplary embodiments described therein.