Assessment of the cell-mediated immunity in cattle infection after bovine herpesvirus 4 infection, using an in vitro antigen-specific interferon-gamma assay.

The cell-mediated immunity (CMI) following bovine herpesvirus 4 (BHV4) infection has been poorly investigated in cattle. The in vivo response measured by a delayed type of hypersensitivity (DTH) assay has been reported to be positive in only few animals showing serological evidences of BHV4 infection. We have investigated the CMI following BHV4 infection by an in vitro antigen-specific interferon gamma (IFN-gamma) release assay, as an indicator of an actively acquired immunity to BHV4. Our preliminary results using a partially purified antigen suggest that there was a measurable CMI in 75 out of 168 animals (44.4%) originating from a farm with a clinical history and serological evidences (76.3% seropositivity) of BHV4 infection. If the results of serological tests and BHV4 IFN-gamma test are interpreted in parallel, 81.5% of the animals are classified positive, demonstrating the complementarity of these tests. The specificity of the BHV4 IFN-gamma test was supported by the absence of a measurable CMI in 41 animals originating from a farm with no clinical history or serological evidence of BHV4 infection. In an allied study, we developed a bovine herpesvirus 1 (BHV1) IFN-gamma test. This allowed us to measure the antigen specific IFN-gamma release after stimulation with a mixture of BHV1 and BHV4 antigens. Animals that were classified negative by the BHV4 IFN-gamma test and by the BHV1 IFN-gamma test, were classified negative after stimulation with a mixture of both antigens. Animals that were classified positive by the BHV4 IFN-gamma test or the BHV1 IFN-gamma test, were classified positive after stimulation with a mixture of both antigens. Taken together these results suggest that the in vitro assessment of the CMI after BHV4 infection should be further investigated as a specific and valuable alternative to the DTH assay.