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Bovine interferon-alphaI1 is an effective inhibitor of bovine herpes virus-1 induced respiratory disease
Antiviral Research, Suppl. 1 (1985) 209-215 Proc. 1st Int. TNO Conf. Antiviral Res. 1985 Rotterdam A. Billiau, E. De Clercq and H. Schellekens (eds.) © 1985 Elsevier Science Publishers B.V. (Biomedical Division)
BOVINE INTERFERON-ALPHAII IS AN EFFECTIVE INHIBITOR OF BOVINE HERPES VIRUS-l INDUCED RESPIRATORY DISEASE CHRISTINE W. CZARNIECKIl, KEVIN P. ANDERSONl, ELIZABETH B. FENNIEl, H. BIELEFELDT OHMANN2, AND LORNE A. BABIUK2 lGenentech, Inc., 460 Point San Bruno Boulevard, South San Francisco, CA 94080 and ZWestern College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Canada 57N OWO INTRODUCTION Interferon-alpha (IFN-a) proteins are encoded by two distinct multigene families (class I and class II) in the bovine genome (5). The conditions that control the expression of these different genes have not been clearly elucidated and it is likely that the presence of multiple subtypes in "natural" bovine IFN preparations has complicated the assessment of in vivo therapeutic potential of these proteins. The cloning and expression in I. coli of bovine interferon-alphaIl (BoIFN-aIl) (5), one member of the class I BoIFN-a gene family has allowed for the production of highly purified single IFN preparations in sufficient quantities for extensive in vitro and in vivo characterization. Crude preparations of BoIFNs have been shown to effectively protect animals against several viruses implicated in bovine respiratory disease (BRD) (6,7). This complex syndrome involves factors such as stress, virus infection, and bacterial colonization of the lung (1,9). Newly weaned calves are subjected to a great degree of stress during the journey to and processing after arrival at the feedlot. The stress can lead to endogenous steroid release, which depresses the animal's immune system. Subsequent virus infection further depresses the immune system and leads to bacterial pneumonia. In this report we show that BoIFN-aIl effectively inhibited the in vitro replication of several viruses that have been implicated in BRD. We also present results indicating that treatment of calves with BoIFN-arl increased their resistance to a combined virus (bovine herpesvirus-I) and bacterial (Pasteurella haemolytica) challenge in a model which mimics the symptoms observed in naturally occurring BRD. MATERIALS AND METHODS Cells and Viruses Madin-Darby bovine kidney (MDBK) and embryonic bovine tracheal (EBTr) cells were grown in Dulbecco's modified Eagle's medium (DMEM) supplemented with 10 percent fetal calf serum. Bovine turbinate (BT) cells which were free from
209
bovine virus diarrhea virus (BVDV) were grown in DMEM supplemented with 5 percent lactalbumin hydrolysate and 10 percent horse serum. Stock preparations of Parainfluenza (PI-3) virus (strain SF4) and the Singer strain of BVDV were grown in BT cells; the Cooper strain of bovine herpesvirus (BHV-1) was grown in MDBK cells; the Indiana strain of vesicular stomatis virus (VSV) was grown in BHK cells. These virus stocks were prepared by infecting cell cultures at an input multiplicity of 0.1 PFU/ml. BHV-1 (strain 108) was grown in Georgia bovine kidney (GBK) cells as described previously (3). The preparation had a titer of 10 7 PFU/ml and was used undiluted for in vivo aerosol challenge. Pasteurella haemolytica (biotype A, serotype 1) was grown in brain heart infusion broth containing 5 percent horse serum (12). Cultures used for challenge were in log phase of growth (6 h culture) and had a titer of 1-2 x 109 colony forming units per ml. Interferon I. coli-derived BoIFN-aIl (5) was greater than 95 percent pure as determined by polyacrylamide gel electrophoresis. IFN titers were determined by virus-induced cytopathic effect inhibition assays in microtiter dishes using MDBK cells challenged with VSV and are expressed in laboratory units based on internal laboratory standards. The specific activity was approximately 1-2 x 10 8 u/ml. RESULTS Effects of BorFN-arl on the Replication of Bovine Viruses The antiviral activity of BoIFN-arl was assessed by measuring inhibitory effects on the replication of several viruses that have been isolated from cattle infected with BRD. BVDV has been classified as as a togavirus; PI-3 is a paramyxovirus; and BHV-l is a type 1 herpes virus. Cell monolayers (2 x 105 cells/23 mm well) were treated with BoIFN-all for 24 h and infected with virus (m.o.i. as indicated). After the 1 h virus adsorption period, cultures were washed with PBS to remove un adsorbed inoculum and refed with medium containin9 BoIFN-all. Virus was harvested 24 h post-infection by freezing cell monolayers plus fluid at -80·C and infectious yields were determined by plaque assay. Virus controls (virus produced in cells receiving no IFN treatment) were included for each dose-response set. Under these conditions, inhibition of cell growth could not be detected. Therefore, the inhibition of virus replication (shown in Table 1) was not a result of decreased cell number. As shown in Table 1, the bovine viruses that were tested demonstrated different sensitivities to BoIFN-aII. VSV required IFN concentrations of <10 u/ml to inhibit replication by 90 percent when cells were infected 210
TABLE 1 BoIFN-o l 1 INHIBITS THE REPLICATION OF BOVINE VIRUSES
Virus VSV BVDV PI-3 BHV-l
Cell Line
M.O.I.
MDBK BT BT EBTr BT EBTr
10 1 1 1 0.1 0.1
Inhibitory IFN Concentration a (units/ml) 1 - 10 103 ± 31 162 ± 62 165 ± 7 > 10 3 ") 10 3
Reduction in Virus Yield b (Log) 3.8 2.3 1.4 1.5 1.0 1.3
a IFN values represent concentrations resulting in 90 percent inhibition of virus yield. Values are expressed as mean ± SEM of duplicate determinations from 3 independent trials. b Lo910 reduction achieved with 10 3 u/ml IFN treatment. at an m.o.i. of 10. In contrast, high IFN concentrations were needed to inhibit BHV-1 replication even when cells were infected at an m.o.i. of 0.1. Evaluation of BoIFN-o l 1 in a Challenge Model for BRD Range bred, healthy Hereford calves aged 6-10 months and weighing 150-250 kg were used. All animals were seronegative for BHV-1 and f. haemolytica and neither of these agents was isolated from the animals prior to challenge. Groups of 5 calves were treated intranasally with placebo or varying doses of BoIFN-a l 1 (1, 5, 10 or 25 mg per animal) 48 h prior to being challenged individually by exposure to an aerosol of BHV-1 virus, followed 4 days later with f. haemolytica as described previously (8). Clinical scores were determined by an investigator who was kept uninformed of the specific treatment of the individual animals. The parameters for evaluation included depression, appetite, fever, conjunctivitis, rhinitis, tracheitis, and dehydration. Arbitrarily, a clinical score of ~ 10 was assigned to animals exhibiting severe disease (those that would be considered sick enough to be placed in a sick pen for individual treatment under feedlot conditions); a value of < 10 was indicative of a moderate infection; and healthy animals were assigned values of O. As shown in Fig. lA, a 1 mg dose did not effectively reduce clinical scores relative to the control placebo group. Mean clinical scores were significantly lower (p<0.05) in groups receiving 5 and 10 mg per animal than in the control group on several days during the study. 211
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Figure 1. Groups of 5 calves treated with BoIFN-aI1, intranasally, on day 1 with excipient (.), 1 (0), 5 (.), 10 (A), or 25 (0) mg and were infected with BHV-1 on day 3 and f. haemolytica on Day 7. (A) Each animal was scored for clinical symptoms as described and the total score for each calf was used to calculate a daily mean for each group. (B) Mean titers of BHV-1 (PFU/ml) in nasal secretions. Animals receiving 25 mg of BoIFN exhibited lower overall clinical scores than the control group, but these differences were not statistically significant. It should also be noted that the calves treated with 5, 10, and 25 mg BoIFN-a I 1 never got as sick as untreated calves and returned to a state of subclinical disease earlier than did untreated animals. There were fewer deaths in the IFN-treated groups, but because of the small number of animals in each group no statistically significant conclusions could be drawn. In this study, plasma fibrinogen levels were also measured as previously described (8). Generally, increased fibrinogen in the plasma correlates with increased lung involvement that occurs with fibrinous pneumonia resulting from pasteurellosis. As shown in Table 2, in calves treated with 5 mg or 10 mg BoIFN-a I 1, the mean levels of plasma fibrinogen were statistically lower (p<0.05) on the final day of the study. The levels of BHV-1 in nasal secretions were measured in an attempt to explain why IFN-treated animals were not as severely affected by the virus-bacterial challenge. Nasal secretions for determination of BHV-1 titers were collected as described previously (11). Briefly, a tampon was inserted into the ventral meatus of the nasal cavity. After approximately 45 min. the tampon was removed and virus titers were determined on GBK cells as described 212
TABLE II Effect of IFN-Treatment on Plasma Fibrinogen Levels BoIFN-aI1 Dose (mg/animal) 0 (placebo) 1 5 10 25
Mean Plasma Fibrinogen (mg/ml) Day 1 Day 13 4.8 4.8 3.6 5.3 5.2
14.3 14.5 8.5 a 10.3 a 11.3
a p<0.05 when compared to control placebo group by unpaired student t test. previously (2). No virus was detected in nasal secretions of any animal 24 h post-infection (data not shown). However, by 48 h post-infection (study day 5) the majority of animals in IFN-treated or control placebo-treated groups shed virus. As shown in Fig. 1B, only one group (5 mg dose) showed reduction in virus shedding and this reduction was not statistically significant. These results are consistent with our earlier findings in which calves treated with multiple intranasal administrations of BoIFN-a I 1 showed reduced levels of BHV-1 in nasal secretions as long as IFN treatments continued. Within 48 h after the last dose of BoIFN-a I 1, BHV-1 levels in nasal secretions approached those in control calves receiving no IFN treatment (data not shown). CONCLUSIONS We have shown that treatment of calves with BoIFN-aI1 effectively reduced the severity of clinical symptoms associated with a combined BHV-1, f. haemolytica challenge. Clinical scores, assigned on the basis of various clinical observations, were dramatically reduced (Fig. 1A). The degree of fibrinous pneumonia as measured by plasma fibrinogen levels was also decreased (Table 2). However, BHV-1 replication in the upper respiratory tract of BoIFN-a I1 treated calves was only marginally affected, even in those animals that were protected against the challenge (Fig. 1B). It is possible that in these studies, BoIFN-a I1 may be exerting a direct antiviral effect in the lung. We have measured virus titers in tracheal washes of calves in only one experiment to date and in that study, statistically significant reductions in BHV-l titers were observed in those BoIFN-a I 1-treated animals most resistant to the challenge (data not shown). However, further experiments are needed to confirm these results. 213
Based on these observations, IFN treatment may prove to be a useful prophylactic treatment for BRD -- one that could be easily implemented in present day feedlot management practices. Calves could be treated upon entry into feedlots at which time most animals are exposed to a variety of viruses responsible for initiating the BRD complex (10). Since (i) of all the viruses implicated in the initiation of this disease, BHV-l is the least sensitive to BoIFN-aI1- induced inhibition (Table 1) and (ii) treatment of calves with BoIFN-aII resulted in reduced symptoms of disease induced by this virus, it appears that treatment with BoIFN-aII may prove even more beneficial with respect to other viruses involved in this disease complex. Field trials conducted under feedlot conditions using intranasal application are necessary to evaluate the effectiveness of BoIFN-aII in the control of BRD and such studies are currently in progress. ACKNOWLEDGEMENTS We gratefully acknowledge H. Chiu for assistance in preparation of this manuscript. REFERENCES 1. Babiuk, L.A. and Acres, S.D. (1984). Models for bovine respiratory disease. In Bovine Respiratory Disease: A Symposium. Ed. R.W. Loan, Texas A+M. Univ. Press. College Station, Texas. pp. 287-325. 2. Babiuk, L.A. and Rouse, B.T. (1976). Immune interferon production by lymphoid cells: role in the inhibition of herpesviruses. Infection Immunity 13, 1567-1578. 3. Babiuk, L.A., Wardley, R.C. and Rouse, B.T. 1975. Defense mechanisms against bovine herpesviruses: relationship of virus-host cell events to susceptibility to antibody complement cell lysis. Infection Immunity 12, 958-963. 4. Bielefeldt Ohmann, H. and Babiuk, L.A. (1985). Viral-bacterial pneumonia in calves: Effect of bovine herpesvirus-Ion immunological functions. Journal Infectious Disease (In press). 5. Capon, D.J., Shepard, H.M., and Goedde1, D.V. (1985). Two distinct classes of human and bovine interferon-a genes are coordinately expressed and encode functional polypeptides. Mol. and Cell. Bio1. 5, 768-779. 6. Cummins, J.M. and Rosenquist, B.D. (1980). Protection of calves against rhinovirus infection by nasal secretion interferon induced by infectious bovine rhinotracheitis. American Journal of Veterinary Research 41, 161-165. 7. Cummins, J.M. and Rosenquist, B.D. (1982). Temporary protection of calves against adenovirus infection by nasal secretion interferon induced by infectious bovine rhinotracheitis virus. Am. J. Vet. Res. 43, 955-959. 8. Garry, F.B. (1984). Plasma fibrinogen measurement: Prognostic value in calf Bronchopneumonia. Zentra1b1att fur Veterinarmedizin, A31, 361-369. 9. Hoer1ein, A.B. and G.L. Marsh. (1957). Studies on the epizootiology of shipping fever in calves. J. Am. Vet. Med. Assoc. 131, 123-127. 214
10. Rosenquist, B.D. (1984). Viruses as etiological agents of bovine respiratory disease. In Bovine Respiratory Disease: A Symposium. Ed. R.W. Loan. Texas A+M Univ. Press, College Station, Texas, pp. 363-376. 11. Todd, J.D., Volence, F.J., and Faton, I.M. (1972). Interferon in nasal secretions and sera of calves after intranasal administration of avirulent infectious bovine rhinotracheitis virus: association of interferon in nasal secretions with early resistance to challenge with virulent virus. Infection and Immunity 5, 699-706. 12. Yates, W.D.G. (1982). A review of infectious bovine rhinotracheitis, shipping fever pneumonia and viral-bacterial synergism in respiratory disease of cattle. Can. J. Compo Med. 46, 225-263.
215
BOVINE INTERFERON-ALPHAII IS AN EFFECTIVE INHIBITOR OF BOVINE HERPES VIRUS-l INDUCED RESPIRATORY DISEASE CHRISTINE W. CZARNIECKIl, KEVIN P. ANDERSONl, ELIZABETH B. FENNIEl, H. BIELEFELDT OHMANN2, AND LORNE A. BABIUK2 lGenentech, Inc., 460 Point San Bruno Boulevard, South San Francisco, CA 94080 and ZWestern College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Canada 57N OWO INTRODUCTION Interferon-alpha (IFN-a) proteins are encoded by two distinct multigene families (class I and class II) in the bovine genome (5). The conditions that control the expression of these different genes have not been clearly elucidated and it is likely that the presence of multiple subtypes in "natural" bovine IFN preparations has complicated the assessment of in vivo therapeutic potential of these proteins. The cloning and expression in I. coli of bovine interferon-alphaIl (BoIFN-aIl) (5), one member of the class I BoIFN-a gene family has allowed for the production of highly purified single IFN preparations in sufficient quantities for extensive in vitro and in vivo characterization. Crude preparations of BoIFNs have been shown to effectively protect animals against several viruses implicated in bovine respiratory disease (BRD) (6,7). This complex syndrome involves factors such as stress, virus infection, and bacterial colonization of the lung (1,9). Newly weaned calves are subjected to a great degree of stress during the journey to and processing after arrival at the feedlot. The stress can lead to endogenous steroid release, which depresses the animal's immune system. Subsequent virus infection further depresses the immune system and leads to bacterial pneumonia. In this report we show that BoIFN-aIl effectively inhibited the in vitro replication of several viruses that have been implicated in BRD. We also present results indicating that treatment of calves with BoIFN-arl increased their resistance to a combined virus (bovine herpesvirus-I) and bacterial (Pasteurella haemolytica) challenge in a model which mimics the symptoms observed in naturally occurring BRD. MATERIALS AND METHODS Cells and Viruses Madin-Darby bovine kidney (MDBK) and embryonic bovine tracheal (EBTr) cells were grown in Dulbecco's modified Eagle's medium (DMEM) supplemented with 10 percent fetal calf serum. Bovine turbinate (BT) cells which were free from
209
bovine virus diarrhea virus (BVDV) were grown in DMEM supplemented with 5 percent lactalbumin hydrolysate and 10 percent horse serum. Stock preparations of Parainfluenza (PI-3) virus (strain SF4) and the Singer strain of BVDV were grown in BT cells; the Cooper strain of bovine herpesvirus (BHV-1) was grown in MDBK cells; the Indiana strain of vesicular stomatis virus (VSV) was grown in BHK cells. These virus stocks were prepared by infecting cell cultures at an input multiplicity of 0.1 PFU/ml. BHV-1 (strain 108) was grown in Georgia bovine kidney (GBK) cells as described previously (3). The preparation had a titer of 10 7 PFU/ml and was used undiluted for in vivo aerosol challenge. Pasteurella haemolytica (biotype A, serotype 1) was grown in brain heart infusion broth containing 5 percent horse serum (12). Cultures used for challenge were in log phase of growth (6 h culture) and had a titer of 1-2 x 109 colony forming units per ml. Interferon I. coli-derived BoIFN-aIl (5) was greater than 95 percent pure as determined by polyacrylamide gel electrophoresis. IFN titers were determined by virus-induced cytopathic effect inhibition assays in microtiter dishes using MDBK cells challenged with VSV and are expressed in laboratory units based on internal laboratory standards. The specific activity was approximately 1-2 x 10 8 u/ml. RESULTS Effects of BorFN-arl on the Replication of Bovine Viruses The antiviral activity of BoIFN-arl was assessed by measuring inhibitory effects on the replication of several viruses that have been isolated from cattle infected with BRD. BVDV has been classified as as a togavirus; PI-3 is a paramyxovirus; and BHV-l is a type 1 herpes virus. Cell monolayers (2 x 105 cells/23 mm well) were treated with BoIFN-all for 24 h and infected with virus (m.o.i. as indicated). After the 1 h virus adsorption period, cultures were washed with PBS to remove un adsorbed inoculum and refed with medium containin9 BoIFN-all. Virus was harvested 24 h post-infection by freezing cell monolayers plus fluid at -80·C and infectious yields were determined by plaque assay. Virus controls (virus produced in cells receiving no IFN treatment) were included for each dose-response set. Under these conditions, inhibition of cell growth could not be detected. Therefore, the inhibition of virus replication (shown in Table 1) was not a result of decreased cell number. As shown in Table 1, the bovine viruses that were tested demonstrated different sensitivities to BoIFN-aII. VSV required IFN concentrations of <10 u/ml to inhibit replication by 90 percent when cells were infected 210
TABLE 1 BoIFN-o l 1 INHIBITS THE REPLICATION OF BOVINE VIRUSES
Virus VSV BVDV PI-3 BHV-l
Cell Line
M.O.I.
MDBK BT BT EBTr BT EBTr
10 1 1 1 0.1 0.1
Inhibitory IFN Concentration a (units/ml) 1 - 10 103 ± 31 162 ± 62 165 ± 7 > 10 3 ") 10 3
Reduction in Virus Yield b (Log) 3.8 2.3 1.4 1.5 1.0 1.3
a IFN values represent concentrations resulting in 90 percent inhibition of virus yield. Values are expressed as mean ± SEM of duplicate determinations from 3 independent trials. b Lo910 reduction achieved with 10 3 u/ml IFN treatment. at an m.o.i. of 10. In contrast, high IFN concentrations were needed to inhibit BHV-1 replication even when cells were infected at an m.o.i. of 0.1. Evaluation of BoIFN-o l 1 in a Challenge Model for BRD Range bred, healthy Hereford calves aged 6-10 months and weighing 150-250 kg were used. All animals were seronegative for BHV-1 and f. haemolytica and neither of these agents was isolated from the animals prior to challenge. Groups of 5 calves were treated intranasally with placebo or varying doses of BoIFN-a l 1 (1, 5, 10 or 25 mg per animal) 48 h prior to being challenged individually by exposure to an aerosol of BHV-1 virus, followed 4 days later with f. haemolytica as described previously (8). Clinical scores were determined by an investigator who was kept uninformed of the specific treatment of the individual animals. The parameters for evaluation included depression, appetite, fever, conjunctivitis, rhinitis, tracheitis, and dehydration. Arbitrarily, a clinical score of ~ 10 was assigned to animals exhibiting severe disease (those that would be considered sick enough to be placed in a sick pen for individual treatment under feedlot conditions); a value of < 10 was indicative of a moderate infection; and healthy animals were assigned values of O. As shown in Fig. lA, a 1 mg dose did not effectively reduce clinical scores relative to the control placebo group. Mean clinical scores were significantly lower (p<0.05) in groups receiving 5 and 10 mg per animal than in the control group on several days during the study. 211
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Figure 1. Groups of 5 calves treated with BoIFN-aI1, intranasally, on day 1 with excipient (.), 1 (0), 5 (.), 10 (A), or 25 (0) mg and were infected with BHV-1 on day 3 and f. haemolytica on Day 7. (A) Each animal was scored for clinical symptoms as described and the total score for each calf was used to calculate a daily mean for each group. (B) Mean titers of BHV-1 (PFU/ml) in nasal secretions. Animals receiving 25 mg of BoIFN exhibited lower overall clinical scores than the control group, but these differences were not statistically significant. It should also be noted that the calves treated with 5, 10, and 25 mg BoIFN-a I 1 never got as sick as untreated calves and returned to a state of subclinical disease earlier than did untreated animals. There were fewer deaths in the IFN-treated groups, but because of the small number of animals in each group no statistically significant conclusions could be drawn. In this study, plasma fibrinogen levels were also measured as previously described (8). Generally, increased fibrinogen in the plasma correlates with increased lung involvement that occurs with fibrinous pneumonia resulting from pasteurellosis. As shown in Table 2, in calves treated with 5 mg or 10 mg BoIFN-a I 1, the mean levels of plasma fibrinogen were statistically lower (p<0.05) on the final day of the study. The levels of BHV-1 in nasal secretions were measured in an attempt to explain why IFN-treated animals were not as severely affected by the virus-bacterial challenge. Nasal secretions for determination of BHV-1 titers were collected as described previously (11). Briefly, a tampon was inserted into the ventral meatus of the nasal cavity. After approximately 45 min. the tampon was removed and virus titers were determined on GBK cells as described 212
TABLE II Effect of IFN-Treatment on Plasma Fibrinogen Levels BoIFN-aI1 Dose (mg/animal) 0 (placebo) 1 5 10 25
Mean Plasma Fibrinogen (mg/ml) Day 1 Day 13 4.8 4.8 3.6 5.3 5.2
14.3 14.5 8.5 a 10.3 a 11.3
a p<0.05 when compared to control placebo group by unpaired student t test. previously (2). No virus was detected in nasal secretions of any animal 24 h post-infection (data not shown). However, by 48 h post-infection (study day 5) the majority of animals in IFN-treated or control placebo-treated groups shed virus. As shown in Fig. 1B, only one group (5 mg dose) showed reduction in virus shedding and this reduction was not statistically significant. These results are consistent with our earlier findings in which calves treated with multiple intranasal administrations of BoIFN-a I 1 showed reduced levels of BHV-1 in nasal secretions as long as IFN treatments continued. Within 48 h after the last dose of BoIFN-a I 1, BHV-1 levels in nasal secretions approached those in control calves receiving no IFN treatment (data not shown). CONCLUSIONS We have shown that treatment of calves with BoIFN-aI1 effectively reduced the severity of clinical symptoms associated with a combined BHV-1, f. haemolytica challenge. Clinical scores, assigned on the basis of various clinical observations, were dramatically reduced (Fig. 1A). The degree of fibrinous pneumonia as measured by plasma fibrinogen levels was also decreased (Table 2). However, BHV-1 replication in the upper respiratory tract of BoIFN-a I1 treated calves was only marginally affected, even in those animals that were protected against the challenge (Fig. 1B). It is possible that in these studies, BoIFN-a I1 may be exerting a direct antiviral effect in the lung. We have measured virus titers in tracheal washes of calves in only one experiment to date and in that study, statistically significant reductions in BHV-l titers were observed in those BoIFN-a I 1-treated animals most resistant to the challenge (data not shown). However, further experiments are needed to confirm these results. 213
Based on these observations, IFN treatment may prove to be a useful prophylactic treatment for BRD -- one that could be easily implemented in present day feedlot management practices. Calves could be treated upon entry into feedlots at which time most animals are exposed to a variety of viruses responsible for initiating the BRD complex (10). Since (i) of all the viruses implicated in the initiation of this disease, BHV-l is the least sensitive to BoIFN-aI1- induced inhibition (Table 1) and (ii) treatment of calves with BoIFN-aII resulted in reduced symptoms of disease induced by this virus, it appears that treatment with BoIFN-aII may prove even more beneficial with respect to other viruses involved in this disease complex. Field trials conducted under feedlot conditions using intranasal application are necessary to evaluate the effectiveness of BoIFN-aII in the control of BRD and such studies are currently in progress. ACKNOWLEDGEMENTS We gratefully acknowledge H. Chiu for assistance in preparation of this manuscript. REFERENCES 1. Babiuk, L.A. and Acres, S.D. (1984). Models for bovine respiratory disease. In Bovine Respiratory Disease: A Symposium. Ed. R.W. Loan, Texas A+M. Univ. Press. College Station, Texas. pp. 287-325. 2. Babiuk, L.A. and Rouse, B.T. (1976). Immune interferon production by lymphoid cells: role in the inhibition of herpesviruses. Infection Immunity 13, 1567-1578. 3. Babiuk, L.A., Wardley, R.C. and Rouse, B.T. 1975. Defense mechanisms against bovine herpesviruses: relationship of virus-host cell events to susceptibility to antibody complement cell lysis. Infection Immunity 12, 958-963. 4. Bielefeldt Ohmann, H. and Babiuk, L.A. (1985). Viral-bacterial pneumonia in calves: Effect of bovine herpesvirus-Ion immunological functions. Journal Infectious Disease (In press). 5. Capon, D.J., Shepard, H.M., and Goedde1, D.V. (1985). Two distinct classes of human and bovine interferon-a genes are coordinately expressed and encode functional polypeptides. Mol. and Cell. Bio1. 5, 768-779. 6. Cummins, J.M. and Rosenquist, B.D. (1980). Protection of calves against rhinovirus infection by nasal secretion interferon induced by infectious bovine rhinotracheitis. American Journal of Veterinary Research 41, 161-165. 7. Cummins, J.M. and Rosenquist, B.D. (1982). Temporary protection of calves against adenovirus infection by nasal secretion interferon induced by infectious bovine rhinotracheitis virus. Am. J. Vet. Res. 43, 955-959. 8. Garry, F.B. (1984). Plasma fibrinogen measurement: Prognostic value in calf Bronchopneumonia. Zentra1b1att fur Veterinarmedizin, A31, 361-369. 9. Hoer1ein, A.B. and G.L. Marsh. (1957). Studies on the epizootiology of shipping fever in calves. J. Am. Vet. Med. Assoc. 131, 123-127. 214
10. Rosenquist, B.D. (1984). Viruses as etiological agents of bovine respiratory disease. In Bovine Respiratory Disease: A Symposium. Ed. R.W. Loan. Texas A+M Univ. Press, College Station, Texas, pp. 363-376. 11. Todd, J.D., Volence, F.J., and Faton, I.M. (1972). Interferon in nasal secretions and sera of calves after intranasal administration of avirulent infectious bovine rhinotracheitis virus: association of interferon in nasal secretions with early resistance to challenge with virulent virus. Infection and Immunity 5, 699-706. 12. Yates, W.D.G. (1982). A review of infectious bovine rhinotracheitis, shipping fever pneumonia and viral-bacterial synergism in respiratory disease of cattle. Can. J. Compo Med. 46, 225-263.
215