Mechanism of T cell-derived helper factor production upon stimulation with pokeweed mitogen in humans.

T cell-derived helper factors can cause activated B cells to proliferate and differentiate into immunoglobulin (Ig)-secreting cells. In the pokeweed mitogen (PWM)-driven Ig production system, the cell-cell interaction necessary for the production of the helper factors was analysed. T cells were pulsed with PWM with or without autologous monocytes. The T cells were then isolated, and incubated for 48 h. Supernatants were tested for their ability to promote differentiation of activated B cells. We found that cell-cell contact between T cells and monocytes for the first 3 h of culture is required to produce the T cell-derived helper factors upon stimulation with PWM. We next examined which T cell subsets are involved in the production of helper factors and which surface molecules either on T cells or on monocytes are responsible for the cell-cell interaction to produce helper factors. A series of monoclonal antibodies were added to T cell subsets with monocytes during the PWM-pulsed period. Although T4+ and T8+ cells could produce almost equal amounts of helper factor activity upon PWM-stimulation, the interactions between T3 and T4 antigens on T4+ cells and Ia-like antigens on monocytes and those between T3 and T8 antigens on T8+ cells and HLA class I antigens on monocytes are respectively essential for the production of T4+ cell-derived and T8+ cell-derived helper factors.