Role of monocytes in pokeweed mitogen-induced differentiation of human peripheral blood lymphocytes

Separate stimulation (“pulsing”) method of different cell populations with pokeweed mitogen (PWM) was used to study the regulatory role of monocytes in the PWM-induced plaque-forming cell response of human peripheral blood lymphocytes. T cells, B cells, and monocytes were separated, pulse-stimulated with PWM, extensively washed, and cocultured with unstimulated cell populations without additional PWM. Pulse-stimulated T cells helped unstimulated B cells to differentiate into immunoglobulin-secreting cells. This generation of helper T cells by PWM-pulsing was enhanced by monocytes in the presence of free PWM, as well as by PWM-pulsed monocytes in the absence of free PWM. A coculture of pulse-stimulated B cells and unstimulated T cells produced more substantial B-cell differentiation than the coculture of stimulated T cells and unstimulated B cells. Further enhancement of the latter response was obtained when B cells were pulse-stimulated in the presence of monocytes. However, pulse-stimulated B cells did not differentiate in the absence of T cells, and monocytes were unable to replace this T-cell function. It appears that there are several pathways by which PWM induces B-cell differentiation and in each, monocytes play an enhancing role.