2′,5′ Oligoadenylate Synthetase Activity in Bovine Peripheral Blood Mononuclear Cells Following Bovine Herpesvirus Type-1-Induced Respiratory Disease: A Prognostic Indicator?

Following aerosol-challenge of nonimmune calves with bovine herpesvirus type-1 (BHV-1) the levels of 2′,5′ oligoadenylate (2-5A) synthetase in peripheral blood mononuclear cells (PBML) increased significantly to peak 4–5 days after BHV-1 infection. This corresponded temporally to the period of highest susceptibility to secondary bacterial infection. Ten days post virus infection, the enzyme levels had returned to baseline values. Aerosol challenge with bacteria (Pasteurella haemolytica) did not induce 2-5A synthetase activity in PBML, neither did it influence the kinetics of 2-5A synthetase induction by virus infection during a dual viral–bacterial infection. Pretreatment of animals with bovine recombinant interferons (IFNs) 0–96 h prior to virus challenge curtailed the viral infection and thus reduced the levels of 2-5A synthetase induced by endogenously produced IFN. A relationship between 2-5A synthetase levels on day 5 post virus infection and clinical outcome of the dual infection was noted. Moreover, the high 2-5A synthetase levels could be correlated with low plasma Zn levels, another indicator of clinical respiratory disease. These results indicate that these two parameters, 2-5A synthetase and plasma Zn, in combination have potential prognostic value in viral–bacterial infections of the respiratory tract.