Bovine lymph node cells (LNC) have been used as a model to study cell activation and proliferation. Because monoclonal antibodies to bovine lymphoid-specific surface antigens have only recently become available, these cells have not been previously characterized in regard to subpopulations. Furthermore, it was not known how expression of lymphoid differentiation antigens and subset proportionalities might change following different modes of activation of LNC. Therefore, the distribution of cell-surface differentation antigens in unstimulated LNC as well as in LNC incubated with the mitogen concanavalin A (Con A) or the phorbol ester, phorbol dibutyrate (PDBU), was measured using a series of leukocyte-specific monoclonal antibodies and flow cytometry. Unstimulated LNC were found to have similar proportions of T cells, B cells (sIgM positive), and MHC Class II positive cells similar to bovine peripheral blood mononuclear leukocytes (reviewed by Baldwin et al., 1988a). Treatment of the LNC with PDBU or mitogenic doses of Con A induced changes in the expression of surface antigens consistent with the changes observed with human and mouse cells after similar activation. However, these two compounds did not cause identical effects. After treatment with PDBU, the percentage of cells expressing CD4 as well as the density of surface expression decreased. An increase in the percentage of cells expressing and/or density of surface expression of the pan T cell antigens CD2, CD5, CD6, MHC Class II and J5, a T cell activation antigen, also occurred. PDBU treatment also increased the percentage of CD8 positive cells. The change in CD6 following PDBU treatment has not been reported previously. Con A treatment led to a significant increase in the percentage of cells bearing CD8, CD6, MHC Class II and J5, but it had no effect on the percentages of cells positive for the other T cell markers CD5, CD4, or CD2. Because Con A is a complete mitogen and PDBU is not, the changes observed following Con A stimulation probably reflected an expansion of a particular subpopulation. In contrast, PDBU most likely modifies surface antigen expression directly. Neither treatment affected the B cell subpopulation.
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