The role of monocyte factors in the differentiation of immunoglobulin secreting cells from human peripheral blood B cells.

Supernatants from cultures of human mononuclear phagocytes (M phi) were found to support pokeweed mitogen- (PWM) induced generation of immunoglobulin-secreting cells (ISC) in cultures of T cell-depleted, human peripheral blood B cells. The M phi factor did not augment PWM-stimulated B cell proliferation. Moreover, M phi factor itself was not a polyclonal B cell activator, in that no ISC were generated unless PWM was present in the B cells cultures. M phi factor release, however, did not require PWM stimulation, but occurred spontaneously under standard conditions used to elicit the PWM response. The active factor found in M phi culture supernatants originated from M phi and not from the few contaminating T cells in the M phi population. M phi factor did not replace the requirement for T cells in this system, however, since factor activity was apparent only when B cell cultures contained a small number of T cells. Finally, M phi factor augmented generation of both IgM and IgG ISC. These data emphasize the important role of M phi in the differentiation of human B cells into ISC and indicate that at least some of the function of M phi in this system is accomplished by secreted factors.