Heterogeneity of human monocyte subsets in the promotion of B cell colonies and the role of interleukin 1.

The abilities of human peripheral blood mononuclear-phagocyte (M phi) subpopulations and of interleukin 1 (IL 1) to support human B cell colony formation in semisolid cultures stimulated by staph protein A were analyzed. Human M phi subsets enriched for complement receptors (CR) effectively functioned as accessory cells supporting colony growth, whereas the responses obtained with CR-depleted M phi were 4.6-fold less. In experiments analyzing IL 1 production, CR-enriched M phi secreted four to 12 fold greater amounts of basal and stimulated IL 1 than CR-depleted M phi. Also, the addition of IL 1 to CR-depleted M phi resulted in a fourfold increase of colony numbers. The responses of cultures containing CR-depleted M phi plus IL 1, however, remained 30% less than those observed for cultures supplemented with CR-enriched M phi. Other studies showed that IL 1 was unable to substitute for M phi; the responses of cultures containing IL 1 and B cells were reduced 10-fold compared to cultures supplemented with autologous M phi. These findings indicate that human M phi subsets exist that differ in their ability to function as accessory cells. Although IL 1 can collaborate with certain M phi subsets to restore their accessory cell function, it cannot replace intact M phi. Thus, it is possible that other monokines or lymphokines play a role in M phi accessory cell function.