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SUMMARYSix monoclonal antibodies (MAbs) to bovine coronavirus (BCV, Quebec isolate) E2 and E3 glycoproteins which were found previously to be neutralizing in vitro were examined for virus-neutralizing activity in vivo. Surgically ligated intostinal loops of newborn colostrum-deprived calves were virus-inoculated, mock-inf6cted or inoculated with a mixture of virus and antibody. Of the six BCV-specific MAbs, four were found to be protective against a virulent field isolate of BCV, as indicated by a reduction in villous atrophy. These MAbs were specific to antigenic domain A and antigenic domains A1 and A2 on the E2 and E3 glycoproteins respectively. MAbs to antigenic domains B and C on the E2 and E3 glycoproteins, respectively, were not protective.

SUMMARYTreatment of calves with bovine recombinant c¢1 interferon prior to challenge with bovine herpesvirus type 1 increased the animals' ability to withstand a subsequent Pasteurella haemolytica challenge. The reduction in viral-bacterial synergy observed following interferon treatment did not appear to be due to a direct effect of the interferon on virus replication in the upper respiratory tract. Thus, even though interferon-treated animals shed slightly less virus from their nasal passages than did untreated animals, this reduction was not statistically significant. Furthermore, there was no difference in the level of intranasal interferon secreted by control or interferontreated animals. These results suggest that interferon treatment does not affect the production of endogenous interferon. In contrast, a significant difference was observed between the number of days that control animals were sick, the levels of serum fibrinogen and the functional activity of polymorphonuclear neutrophilic granulocytes obtained from infected calves. These results suggest that bovine recombinant ~1 interferon may have a greater immunomodulatory effect than a direct antiviral effect in this model. This is further supported by the observation that bovine herpesvirus type 1 is relatively resistant to the direct antiviral effect of bovine recombinant ~1 interferon in vitro.

Intranasal or intramuscular treatment of calves with recombinant bovine alpha, interferon before challenge with bovine herpesvwrus type 1 and Pasteurella haemolytica reduced clinical signs, number of sick days, lung lesions, and weight loss. The effective dose was determined to be relatively broad within the range of 1 to 50 mg per animal. No adverse effects were observed even at high doses of interferon (50 mg per animal). Administration before virus infection was more effective than administration at the same time as virus infection. Although interferon administration had dramatic effects on the survival of animals, it did not have much effect on virus secretion in the upper respiratory tract. Therefore, the mechanism by which interferon reduces the susceptibility of animals to viral-bacterial synergy was postulated to be via its immunomodulatory effects.