Modulatory effects of plasma and serum on T lymphocyte activation: distinctive patterns for different mitogens

Published reports have shown that fresh plasma, but not cryoprecipitate-depleted plasma or fresh serum, inhibits T cell activation by phytohemagglutinin (PHA). We sought to determine if this pattern of inhibition also characterized T cell responses to mitogens differing from PHA with regard to the cell surface molecules utilized for signal transduction. The activation system included colchicine, which limits the cells to one round of division, masking stimulatory factors that enhance proliferation by boosting the number of divisions per culture period. A distinctive modulatory pattern characterized T cell responses to each of 4 mitogens tested (PHA, anti-CD3 monoclonal antibody, desialyzed oxidized erythrocytes (DOE), pokeweed mitogen). Enhanced proliferative responses to anti-CD3 and DOE were observed in the presence of serum, and reflected an increased percentage of T cells expressing CD25. These findings suggest that concerns regarding a negative impact of plasma components on T cell responsiveness, when based on results from PHA-induced activations systems, may be unwarranted.