Virus-specific effects of recombinant porcine interferon-gamma and the induction of Mx proteins in pig cells

Human Chorionic Gonadotrophin (hCG) induces changes in IFN-pathway and Interferon-Stimulated Genes (ISGs) on the bovine endometrium at Day 18 of pregnancy

We hypothesized that the hCG modulates the expression of IFNT-pathway and ISGs in bovine endometrium during early pregnancy. The aim of the current study is to evaluate the effect of hCG on IFNT-pathway signals and ISGs expression in endometrial cells. For this, 29 non-lactating cross-bread cows were used in the study and submitted to a 9-day fixed-time artificial insemination (FTAI) protocol. The day of the AI was considered Day 0 (D0), and five days (D5) after the FTAI, the cows were allocated into two groups: Control and hCG group, when a hCG group received a single dose of 2.500UI of hCG. On day 18 after FTAI (D18) cows were slaughtered and endometrial tissue samples were collected. There was no difference between the embryo recovery rate of the cows in C compared to the hCG. The hCG group increased the accessory corpus luteum formation rate. The hCG resulted in greater serum progesterone concentration in the hCG group compared to the C on Day 14. Only the expression of IFNAR2 and STAT1 were upregulated on pregnant cows of the hCG group compared to the C group. The pathway genes (JAK1, STAT2, and IRF9) were not regulated. The mRNA abundance of ISG15, MX1, MX2, and OAS1 was upregulated in pregnant cows for hCG group, compared to C group. The results show that the administration of hCG, 5 days after AI, in addition to increasing the serum progesterone, modulates the expression of IFNT-pathway and ISGs on bovine endometrium on Day 18 of pregnancy.

Inhibitory effects of recombinant porcine interferon-α on porcine transmissible gastroenteritis virus infections in TGEV-seronegative piglets

Our previous research obtained purified recombinant porcine interferon-α (rPoIFN-α) containing thioredoxin (Trx) fusion tag in E. coli Rosetta (DE3). Here, we evaluate the efficacy of this rPoIFN-α to prevent piglets from the infection of the transmissible gastroenteritis virus (TGEV) attack. In this experiment, twenty-five TGEV-seronegative piglets were randomly divided into five groups. Group 1 was positive control and only challenged with TGEV; Pigs in groups 2-4 were pretreated with 2 × 10(7)IU/pig, 2 × 10(6)IU/pig, and 2 × 10(5)IU/pig rPoIFN-α before TGEV challenge. The fifth group is a negative control group. The animals of this group are pretreated only with Trx protein-containing PBS solution without TGEV challenge. After 48 h of rPoIFN-α pretreatment, the pigs in groups 1-4 were challenged by TGEV, and the pigs in group 5 were administered with PBS. The surveillance results show that Pigs pre-treated with 2 × 10 (7) IU/pig rPoIFN-α are fully aligned with the violent TGEV attack. Pigs pretreated with 2 × 10 (6) IU/pig rPoIFN-α are partially aligned with the violent TGEV attack. Though piglets pretreated with 2 × 10(6) IU/pig or 2 × 10(5)IU/pig rPoIFN-α cannot be adapted to the challenge of TGEV. However, the use of this dose of rPoIFN-α could put off the clinical signs of pigs than the positive control group of the above. These results indicate that rPoIFN-α can protect pigs from the infection of potential TGEV or delay the appearance of clinical symptoms, and its effect is dose-dependent.

Experimental Evaluation of the Transport Mechanisms of PoIFN-α in Caco-2 Cells

For the development of an efficient intestinal delivery system for Porcine interferon-α (PoIFN-α), the understanding of transport mechanisms of which in the intestinal cell is essential. In this study, we investigated the absorption mechanisms of PoIFN-α in intestine cells. Caco-2 cells and fluorescein isothiocyanate-labeled (FITC)-PoIFN-α were used to explore the whole transport process, including endocytosis, intracellular trafficking, exocytosis, and transcytosis. Via various techniques, the transport pathways of PoIFN-α in Caco-2 cells and the mechanisms were clarified. Firstly, the endocytosis of PoIFN-α by Caco-2 cells was time, concentration and temperature dependence. And the lipid raft/caveolae endocytosis was the most likely endocytic pathway for PoIFN-α. Secondly, both Golgi apparatus and lysosome were involved in the intracellular trafficking of PoIFN-α. Thirdly, the treatment of indomethacin resulted in a significant decrease of exocytosis of PoIFN-α, indicating the participation of cyclooxygenase. Finally, to evaluate the efficiency of PoIFN-α transport, the transepithelial electrical resistance (TEER) value was measured to investigate the tight junctional integrity of the cell monolayers. The fluorescence microscope results revealed that the transport of PoIFN-α across the Caco-2 cell monolayers was restricted. In conclusion, this study depicts a probable picture of PoIFN-α transport in Caco-2 cells characterized by non-specificity, partial energy-dependency and low transcytosis.

Expression of Mx Protein and Interferon-α in Pigs Experimentally Infected with Swine Influenza Virus

Expression of Mx protein and interferon-α (IFN-α) was examined by immunohistochemistry in pigs experimentally infected with swine influenza virus. In infected pigs euthanatized at 1 day postinoculation (dpi), the lumen of bronchioles were filled with large numbers of mononuclear cells, small numbers of neutrophils, sloughing epithelial cells, and proteinaceous fluid. Lesions at 3 and 5 dpi were similar but less severe. Alveolar spaces were filled with neutrophils. By 7 and 10 dpi, microscopic lesions were resolved. The immunohistochemical signals for Mx protein and IFN-α antigen were confined to cells in areas that had hybridization signal for swine influenza virus. In situ hybridization and immunohistochemistry of serial sections of lung indicated that areas containing numerous swine influenza virus RNA-positive cells also have numerous Mx and IFN-α antigen-positive cells. Mean immunohistochemical scores for Mx protein-positive cells were correlated with mean immunohistochemical scores for IFN-α antigen-positive cells ( rs = 0.8799, p < 0.05). These results indicated that Mx protein and IFN-α antigen were expressed in the lung from pigs experimentally infected with swine influenza virus, but their biological functions remain to be examined.

Production of transgenic pigs over-expressing the antiviral gene Mx1

The myxovirus resistance gene (Mx1) has a broad spectrum of antiviral activities. It is therefore an interesting candidate gene to improve disease resistance in farm animals. In this study, we report the use of somatic cell nuclear transfer (SCNT) to produce transgenic pigs over-expressing the Mx1 gene. These transgenic pigs express approximately 15–25 times more Mx1 mRNA than non-transgenic pigs, and the protein level of Mx1 was also markedly enhanced. We challenged fibroblast cells isolated from the ear skin of transgenic and control pigs with influenza A virus and classical swine fever virus (CFSV). Indirect immunofluorescence assay (IFA) revealed a profound decrease of influenza A proliferation in Mx1 transgenic cells. Growth kinetics showed an approximately 10-fold reduction of viral copies in the transgenic cells compared to non-transgenic controls. Additionally, we found that the Mx1 transgenic cells were more resistant to CSFV infection in comparison to non-transgenic cells. These results demonstrate that the Mx1 transgene can protect against viral infection in cells of transgenic pigs and indicate that the Mx1 transgene can be harnessed to develop disease-resistant pigs.

Plasmids expressing porcine interferon gamma up-regulate pro-inflammatory cytokine and co-stimulatory molecule expression which are suppressed by porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) suppresses the pro-inflammatory immune response following infection of myeloid antigen-presenting cells. A reduced pro-inflammatory immune response modulates PRRSV replication, clinical disease, and persistent infection of the virus. Numerous efforts have been made to enhance the pro-inflammatory immune response to PRRSV, but only a few attempts have so far elicited satisfactory results. The present study aims to evaluate in vitro the potential of plasmids expressing porcine interferon gamma (pcDNA-IFNγ) to enhance the expression of pro-inflammatory immune parameters in PRRSV-inoculated monocytes. Naïve blood monocytes from eight PRRSV-seronegative pigs were inoculated with PRRSV and subsequently transfected with pcDNA-IFNγ or pcDNA (empty plasmid vector) and stimulated with lipopolysaccharide (LPS). The mRNA expression levels of IFNγ, interleukin-1 beta (IL-1β), IL-10, IL-12p40, tumor necrosis factor alpha (TNFα), transforming growth factor beta (TGFβ), CD80, and CD86 were evaluated by real-time PCR. The IFNγ, IL-10, and TNFα protein production was determined by ELISA. Compared with PRRSV-inoculated monocyte control, transfection with pcDNA-IFNγ, but not pcDNA, significantly enhanced IFNγ, TNFα, CD80, and CD86 mRNA expression, and IFNγ and TNFα protein production. A slight increase in IL-1β and IL-12p40 mRNA expression was also observed. Neither pcDNA-IFNγ nor pcDNA transfection affected IL-10 and TGFβ expression. Our results thus suggest that pcDNA-IFNγ may be an effective immunostimulator for potentiating the pro-inflammatory immune response to PRRSV.

Enhanced protection against infection with transmissible gastroenteritis virus in piglets by oral co-administration of live attenuated Salmonella enterica serovar Typhimurium expressing swine interferon-α and interleukin-18

The enhanced effect of cytokine combinations has been assessed empirically, based on their immunobiological mechanisms. However, far less is known of the enhanced protection of practical cytokine combinations against viral infection in the livestock industry, due to cost and production issues associated with mass administration. This study demonstrates the enhanced protection of oral co-administration of swine interferon-α (swIFN-α) and interleukin-18 (swIL-18) against infection with transmissible gastroenteritis virus (TGEV) in piglets using attenuated Salmonella enterica serovar Typhimurium as carrier of cytokine proteins. A single oral co-administration of S. enterica serovar Typhimurium expressing swIFN-α and swIL-18 induced enhanced alleviation of the severity of diarrhea caused by TGEV infection, compared to piglets administered S. enterica serovar Typhimurium expressing swIFN-α or swIL-18 alone. This enhancement was further observed by the reduction of TGEV shedding and replication, and the expression of IFN-stimulated gene products in the intestinal tract. The results suggest that the combined administration of the swIFN-α and swIL-18 cytokines using attenuated S. enterica serovar Typhimurium as an oral carrier provides enhanced protection against intestinal tract infection with TGEV.

Macaque proteome response to highly pathogenic avian influenza and 1918 reassortant influenza virus infections

The host proteome response and molecular mechanisms that drive disease in vivo during infection by a human isolate of the highly pathogenic avian influenza virus (HPAI) and 1918 pandemic influenza virus remain poorly understood. This study presents a comprehensive characterization of the proteome response in cynomolgus macaque (Macaca fascicularis) lung tissue over 7 days of infection with HPAI (the most virulent), a reassortant virus containing 1918 hemagglutinin and neuraminidase surface proteins (intermediate virulence), or a human seasonal strain (least virulent). A high-sensitivity two-dimensional liquid chromatography-tandem mass spectroscopy strategy and functional network analysis were implemented to gain insight into response pathways activated in macaques during influenza virus infection. A macaque protein database was assembled and used in the identification of 35,239 unique peptide sequences corresponding to approximately 4,259 proteins. Quantitative analysis identified an increase in expression of 400 proteins during viral infection. The abundance levels of a subset of these 400 proteins produced strong correlations with disease progression observed in the macaques, distinguishing a "core" response to viral infection from a "high" response specific to severe disease. Proteome expression profiles revealed distinct temporal response kinetics between viral strains, with HPAI inducing the most rapid response. While proteins involved in the immune response, metabolism, and transport were increased rapidly in the lung by HPAI, the other viruses produced a delayed response, characterized by an increase in proteins involved in oxidative phosphorylation, RNA processing, and translation. Proteomic results were integrated with previous genomic and pathological analysis to characterize the dynamic nature of the influenza virus infection process.

Live attenuated Salmonella enterica serovar Typhimurium expressing swine interferon-alpha has antiviral activity and alleviates clinical signs induced by infection with transmissible gastroenteritis virus in piglets

Enhancing innate and acquired immunity by cytokines such as IFN-alpha appears to be useful as a first line of defense against viral infection. However, the practical use of cytokines in livestock is not evident due to cost and production issues associated with mass administration. In this study, we tested the efficacy of live attenuated Salmonella enterica serovar Typhimurium designed to secrete swine IFN-alpha (swIFN-alpha) protein for preventing the clinical signs caused by infection with transmissible gastroenteritis virus (TGEV), one of the diarrhea-causing viruses in the swine industry. Attenuated Salmonella vaccine (chi8501) containing swIFN-alpha-encoding pYA3560 vector (chi8501/swIFN-alpha) successfully induced the secretion of swIFN-alpha protein into the culture supernatants, as confirmed by SDS-PAGE and Western blot. The culture supernatants of chi8501/swIFN-alpha had antiviral activity against TGEV with 50% effective dose (ED(50)) of 320 per mg of supernatant protein. In addition, oral administration of chi8501/swIFN-alpha reduced the severity of clinical signs caused by TGEV infection with the effect more apparent at 6-8 days post-infection, and reduced excretion of TGEV in feces. Similarly, the amount of TGEV in intestinal tissues and mesenteric lymph node of chi8501/swIFN-alpha-administered piglets was lower than in piglets that were treated with control bacteria. These results indicate the value of attenuated Salmonella vaccines as delivery systems of cytokines that can be used for mass administration, thereby overcoming cost and production issues.

Secretory expression of porcine interferon-gamma in baculovirus using HBM signal peptide and its inhibition activity on the replication of porcine reproductive and respiratory syndrome virus

The gene sequence encoding mature porcine interferon-gamma (PoIFN-gamma) fused with a C-terminal 6x histidine tag was cloned into the baculovirus pFastBac Dual vector of the Bac-to-Bac Baculovirus expression system under the control of PH promoter. The authentic signal sequence of porcine interferon-gamma was substituted with the honeybee melittin (HBM) signal sequence, and expressed in insect cells. The recombinant proteins were detected by SDS-PAGE and immunofluorescence assay. The nickel affinity column purified recombinant porcine interferon-gamma with HBM signal peptide (rPoIFN-gammaH) was shown to be a 19kDa protein as confirmed by Western blot analysis. The recombinant PoIFN-gammaH was shown to have cytokine activity, inhibiting the cytopathic effect of vesicular stomatitis virus (VSV) in PK-15 cells at about 1.07x10(6)U/mL. The 2(-7) dilution of the rPoIFN-gammaH in culture supernatant protected the MARC-145 cells from the cytopathic effect caused by 100TCID(50) of porcine reproductive and respiratory syndrome virus.

Adjuvants for porcine reproductive and respiratory syndrome virus vaccines

This review deals with present and past efforts in utilization of vaccine adjuvants for porcine reproductive and respiratory syndrome virus (PRRSV) vaccines. PRRSV vaccines elicit delayed and weak cell-mediated immune (CMI) and antibody responses after vaccination. Several kinds of vaccine adjuvants have been utilized to accelerate and magnify immune responses to PRRSV vaccines. These adjuvants include cytokines, chemical reagents, and bacterial products. Of 11 vaccine adjuvants tested, five (i.e. interleukin-2 (IL-2), IL-12, interferon alpha (IFNalpha), polyinosinic and polycytidylic acid, and cytidine-phosphate-guanosine oligodeoxynucleotides (CpG ODN)) significantly enhance CMI response to PRRSV vaccines. The response is characterized by proliferation, cytotoxicity, and IFNgamma secretion of peripheral blood mononuclear cells or T cells in response to recall PRRSV antigens in vitro. Two (i.e. CpG ODN and cholera toxin) significantly enhance PRRSV-specific antibody response after vaccination. Two (i.e. IL-2 and CpG ODN) significantly enhance protective efficacy of PRRSV vaccines in challenge models. Improvement of immune responses to PRRSV vaccines should focus in future studies on assessing more vaccine adjuvants for their efficiency in enhancing both CMI and antibody responses and on identifying PRRSV components and strategies that down-modulate pig immune responses in order to devise vaccine adjuvants that can regulate such strategies of the virus.

Polymorphisms in the promoter region of the porcine antiviral MX1 and MX2 genes

The porcine MX1 and MX2 promoters were characterized in this study. Sequencing of the 332-bp MX1 promoter region identified 15 substitutions and insertions at three positions in 21 pigs from 15 breeds, in which nine genotypes were classified. Among the nine genotypes, no statistically significant differences in the promoter activities were observed after interferon (IFN-alpha 2b) treatment of transiently transfected cells containing constructs with luciferase reporter plasmids. The 341-bp MX2 promoter region contained regulatory sequences for ISRE, GC box, Sp1 and AP-1, as well as a TATA box. Nucleotide sequences of the MX2 promoter region revealed four substitutions and one deletion, in which six genotypes were classified. Among the six genotypes, a statistically significant difference (P < 0.05) in MX2 promoter activities after IFN-alpha 2b treatment was detected in transiently transfected cells.

A missense polymorphism in porcine interferon-gamma cDNA affects antiviral activity of the protein variant

We determined the interferon-γ (IFN-γ) cDNA sequence from three porcine breeds, Duroc, Landrance/Duroc hybrid, and Landrance breeds. Five single nucleotide polymorphisms (SNPs) of porcine IFN-γ (PoIFN-γ) were identified, respectively, at positions 269 (A/G), 376 (C/T), 426 (T/C), and 465 (T/C) of the coding sequence in Landrance/Duroc hybrid, and at position 251 (A/G) in Landrance breed. Among them, A269G and A251G polymorphisms resulted in Q67R and K61R replacements in the mature protein. PoIFN-γ cDNAs of Duroc breed (PoIFN-γ-W) and Landrance/Duroc hybrid (PoIFN-γ-M), which, respectively, encoded Q67 and R67, were introduced into a prokaryotic expression vector pET32 to express recombinant PoIFN-γ-W (rPoIFN-γ-W) and rPoIFN-γ-M protein variants in Escherichia coli. The identity of both protein variants was further confirmed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). We then compared bioactivities of these two recombinant proteins. Although both recombinant protein variants exhibited comparable activities in antiproliferation of PK-15 cells and in nitric oxide (NO) induction of porcine peripheral monocytes, antiviral activity of rPoIFN-γ-W protein was significantly higher (P < 0.001) than that of rPoIFN-γ-M protein in a plaque inhibition assay using pseudorabies virus (PRV). IC50 values of rPoIFN-γ-W and rPoIFN-γ-M protein in anti-PRV assay were determined as 5.3 ± 1.3 and 9.3 ± 4.3 nM, respectively.

In conclusion, we have identified five novel SNPs in PoIFN-γ cDNA, including two missense polymorphisms that result in Q67R and K61R replacements. Our results further demonstrate that Q67R can markedly reduce antiviral activity of the PoIFN-γ protein. This is the first report that shows the functional SNP in the coding region of IFN-γ. In the future, it is imperative to determine whether Q67R replacement in IFN-γ may have disease association.

Cloning and expression of interferon-alpha/gamma from a domestic porcine breed and its effect on classical swine fever virus

To further evaluate the clinical impact of recombinant PoIFN-alpha/gamma, PoIFN-alpha/gamma genes from a Chinese domestic big-white porcine breed were cloned using PCR, and expressed in a high-level prokaryotic system. The antiviral activities of rPoIFN-alpha/gamma on vesicular stomatitis virus (VSV), porcine reproductive and respiratory syndrome virus (PRRSV), and classical swine fever virus (CSFV) were investigated in different cell lines. The cloned PoIFN-alpha gene encodes a protein of 166 amino acids and has been named PoIFN-alphac. In a comparison of PoIFN-alphac with reported PoIFN-alphaI genes, eight amino acid substitutions at positions 43 (F to L), 78 (N to D), 86 (Y to C), 104 (A to V), 118 (R to L), 128 (T to P), 151 (S to V), and 156 (R to T) were observed, and resulted in no potential N-glycosylation site in the deduced PoIFN-alpha amino acid sequences. In contrast to PoIFN-alphac, one nucleotide substitution was found at position 462 (A to G), hence 0.1% synonymity is specific for the PoIFN-gamma gene. Both PoIFN-alphac and PoIFN-gamma genes were inserted into a prokaryotic vector pQE30, and expressed in E. coli M15 (pREP4) or SC11103 (pREP4) with the N-terminal six consecutive histidine residues, respectively. rPoIFN-alphac and rPoIFN-gamma proteins were detected by SDS-PAGE and Western blotting analysis at 20.7 and 18.0 kDa, respectively. In addition, the rPoIFN-alphac and rPoIFN-gamma protein were purified using Ni-NTA metal-affinity chromatography, and their anti-VSV, anti-PRRSV, and anti-CSFV activities were surveyed in homologous and heterologous cell lines. The results suggested that rPoIFN-alpha and rPoIFN-gamma could inhibit classical swine fever virus and other important viral pathogens in different cell lines.

Expression of interferon-alpha and Mx1 protein in pigs acutely infected with porcine reproductive and respiratory syndrome virus (PRRSV)

The expression of mRNA encoding interferon-alpha (IFN-alpha) and Mx1 protein was studied, by reverse transcription-polymerase chain reaction and by in-situ hybridization with a non-radioactive digoxigenin-labelled cDNA probe, in formalin-fixed, paraffin wax-embedded lung tissue from pigs experimentally infected with a Korean isolate (North American genotype) of porcine reproductive and respiratory syndrome virus (PRRSV). The animals were examined over a period of 10 days after intranasal inoculation. IFN-alpha and Mx1 protein was detected in the lung at 1 day post inoculation (dpi), the number of positive cells increasing at 7dpi, and rapidly decreasing thereafter. Hybridization signals for IFN-alpha and Mx1 protein were usually associated with inflammation, and in particular with macrophages. Expression of IFN-alpha and Mx1 protein was negative in non-lesional lung of PRRSV-infected pigs and in normal lung from control pigs. There was a good statistical correlation between the number of cells positive for mRNA encoding IFN-alpha and Mx1 protein in the infected lungs (r = 0.95, P< 0.05). The results suggest that the expression of IFN-alpha and Mx1 protein plays a role in the early host defence against PRRSV infection.

Polymorphisms and the antiviral property of porcine Mx1 protein

We determined the cDNA sequences of the type I interferon-inducible proteins, pig Mx1 from PK(15) and LLC-PK1 cells, and compared the antiviral activities of both Mx proteins, including Mx1 polymorphisms against vesicular stomatitis virus (VSV). Mx1 cDNA derived from PK(15) cells had an 11 bp-deletion in the 3' end of the coding region, and was estimated to encode 8 amino acid substitutions and a 23 amino acid extension compared to that from LLC-PK1 cells. VSV replication was inhibited in the 3T3 cells expressing Mx1 mRNA after the cDNA was transfected. However, the efficiency of this inhibition was not different between the cells expressing Mx1 mRNA from both PK and LLC. These results indicate that pig Mx1 protein confers resistance to VSV.

Interferon response in pigs: molecular and biological aspects

This paper reviews the current state of knowledge on porcine interferons (IFN). Three type I IFN subfamilies (IFN alpha, beta and omega) and one type II IFN (IFN gamma) have been identified in the porcine species. A list of the known porcine IFN genes and already produced recombinant proteins, as compiled from the literature, was included. Two major aspects of porcine IFN were discussed: (1) IFNs as host responses to infections, and (2) IFNs in pregnancy. The first part mainly focusses on the IFN production by virus-infected pigs and the nature of IFN alpha secreting leukocytes. The second part reviews recent data showing the secretion of two different IFNs by the pig embryo at the time of implantation. One striking finding was that a non-lymphoid tissue, namely the porcine trophoblast, was able to secrete high levels of IFN gamma. In addition, the expression of another, newly described, IFN gene was also shown in pig trophectoderm. This novel trophoblastic type I IFN differs from the others in size and sequence. Several hypotheses are discussed on the possible role(s) of porcine embryonic IFNs at the initial stages of gestation.

Proteins induced by recombinant equine interferon-beta 1 within equine peripheral blood mononuclear cells and polymorphonuclear neutrophilic granulocytes

Peripheral blood mononuclear cells (PBMC) and polymorphonuclear neutrophilic granulocytes (PMN) as well as embryonic equine dermal fibroblasts and the equine fibroblast line E. Derm which were used as controls, were treated with recombinant equine interferon-beta 1 (rEqIFN-beta 1) in vitro which induced the expression of different proteins in these cells. A 74 kDa protein was induced in PBMC and an 82 kDa protein was additionally found in the equine fibroblast E. Derm cell line following treatment with rEqFN-beta 1. Both proteins reacted with anti-mouse and anti-human Mx protein antisera in immunoblot tests. The 74 kDa and perhaps the 82 kDa components may thus represent equine 'Mxanalogous proteins'. The 74 kDa protein was only detected in PBMC of ten out of 20 horses examined. The induction of Mx protein in the horse by Type 1 interferon may therefore resemble that in the mouse, where Mx protein is involved in selective resistance to influenza virus. The influence of rEqIFN-beta 1 on protein expression in equine PBMC and PMN was monitored by metabolic labeling and 2-D gel electrophoresis. Proteins of 82, 74, 58 and 40 kDa were induced in PBMC following exposure to rEqIFN-beta 1. A constitutively expressed 35 kDa protein, however, was no longer demonstrable upon treatment with interferon. None of the proteins induced within PBMC was found in highly purified PMN treated with interferon. PMN exposed to rEqIFN-beta 1 synthesized four proteins in the range of 25 to 27 kDa. These proteins have not been described in interferon-treated PMN of any other species.