Proliferation and phenotype of bovine mononuclear leukocytes in cultures stimulated by pokeweed mitogen.

Cell proliferation and phenotype were evaluated at 2, 4, 6, 8, 10, 12, and 14 d in cultures of bovine peripheral blood mononuclear leukocytes stimulated by pokeweed mitogen. Cell numbers in unstimulated and stimulated 2-d cultures decreased to about 45% of the number originally added. Cell numbers at 6 d in stimulated cultures increased to 96% of the number originally seeded and remained elevated from 6 to 14 d in cultures. In contrast, numbers in unstimulated cultures at 4 to 14 d decreased; < 20% of the original number remained at 14 d. The increase in cell numbers in stimulated cultures from 4 and 6 d was due primarily to an increase in CD2+ T cells, specifically the CD4+ T-cell subset. Proliferation of interleukin-2 receptor+ and major histocompatibility class II antigen+ cells increased in these cultures. Expression of these antigens decreased in unstimulated cultures. The B-cell numbers in stimulated cultures at 2 to 4 d increased and then stabilized. Concentrations of IgM in stimulated 14-d cultures were 5 to 15 times those in parallel unstimulated cultures. Overall, IgM secretion induced by pokeweed mitogen by B cells in cultures of bovine mononuclear leukocyte is associated with proliferation of CD4+ (helper-inducer) T cells, B cells, and increased expression of activation antigens.