Proliferative responses of peripheral blood lymphocytes to polyclonal activation: a comparison of young and elderly individuals.

Associated with human aging is a decline in immune activity, of both the cell-mediated and humoral types. In vivo, autoantibodies increase with aging and antibody responses to flagellin are decreased in the elderly as compared to the young. These abnormalities may be due to defects in helper or suppressor T cells, or innate defects in B cells. In vitro, the proliferative response of B cells to pokeweed mitogen (PWM) is dependent upon T cells. We studied the proliferative response of peripheral blood mononuclear cells (MNC) to polyclonal activation with PWM in young and elderly normal individuals and found that the number of IgA- and IgM-bearing B cells produced was increased in elderly subjects. This difference was statistically significant for IgA-bearing cells when MNC were placed with 5 and 15 microliter of PWM for 5 days and with 15 microliter of PWM for 6 days. Statistically significant increases in IgM-bearing cells were seen when MNC were plased with 5 microliter of PWM for 5 days and 5 and 10 microliter of PWM for 7 days. The differences in numbers of IgG-bearing cells were less consistent. Significant increases were seen when MNC were cultured with 10 microliter of PWM for 5 days and 5 microliter of PWM for 6 days. Our results suggest that in elderly normal individuals numbers of immunoglobulin-bearing cells are increased after polyclonal activation of MNC. This increase in immunoglobulin-bearing B cells associated with reports of in vivo humoral abnormalities suggests that there is loss of regulation of T cells on B cells in normal elderly individuals.