Cellular interactions regulating the in vitro response of bovine lymphocytes to ovalbumin

We examined the contribution of MHC class II-restricted T cells (CD4+), MHC class I-restricted T cells (CD8+), gamma/delta T cell receptor (TCR)+ T cells, B cells and macrophages to the development and control of in vitro proliferative responses of bovine lymphocytes to ovalbumin (OA). Cell populations for in vitro assay were obtained from peripheral blood (peripheral blood leukocytes, PBL) of OA-primed cattle. Specific cell populations were depleted or purified from PBL by staining with monoclonal antibodies (MAbs) against the appropriate differentiation antigens and sorting on a Fluorescence Activated Cell Sorter (FACS). OA-specific in vitro responses of in vivo primed PBL were dependent on the presence of CD4+ T cells. Their presence could not be replaced by the inclusion of T cell growth factor (TCGF) in the culture system, indicating that CD4+ T cells probably actively proliferate in response to antigenic stimulation. Bovine CD8+ T cells and gamma/delta TCR+ T cells appeared to exert a suppressive effect on proliferative responses. No proliferation was observed in PBL after the depletion of MHC class II+ cells. In this case, the response could be restored by the addition of macrophages or LPS-activated B cells to the MHC class II- population.