Patterns of bovine T cell-mediated immune responses to bovine herpesvirus 1

Lymphocyte proliferation was used to evaluate T cell-mediated immune responses to different isolates of Bovine Herpesvirus 1 (BHV-1). Groups of high, moderate, and low responses were observed when lymphocytes from three breeds of dairy cattle were stimulated with each of the BHV-1 isolates. Proliferation of cells in the low responding group could be augmented by exogenous IL-2. The mechanism of unresponsiveness by cells from one individual whose response was not altered by IL-2 supplementation was further investigated. The patterns of response by limiting dilution frequency analysis eliminated the possibility that this individual lacked responsive cells but suggested the presence of regulatory cell interactions which resulted in the observed low proliferative response. These results show that animals exposed to the same environment can vary greatly in their ability to respond to BHV-1. At least two mechanisms may be responsible for low proliferative responses in vitro: inadequate levels of IL-2 and the presence of suppressor cells.