Human B cell differentiation. IV. Effect of monoclonal anti-immunoglobulin M and D antibodies on B cell proliferation and differentiation induced by T cell factors.

Monoclonal anti-mu and anti-delta antibodies and mixed lymphocyte reaction-derived T cell factors (MLR-TF) were examined alone and in combination for their effects on proliferation and differentiation of human B cells. MLR-TF induced proliferation and subsequent plasma cell differentiation of blood B cells without additional stimulation. The monoclonal anti-mu and anti-delta antibodies alone did not induce proliferation, but each was capable of augmenting B cell proliferation induced by MLR-TF. In contrast, the anti-mu antibody inhibited the MLR-TF induction of IgM plasma cell differentiation but did not affect the differentiation of IgG and IgA plasma cells. The anti-delta antibody had no effect on MLR-TF-induced plasma cell differentiation. Studies using density gradient separation of B cell subpopulations suggest that MLR-TF induce low-density B cells to proliferate and differentiate into plasma cells but that by themselves MLR-TF have little effect on B cells of relatively high density. The latter subpopulation of small resting B cells responded with proliferation to MLR-TF when combined with either the anti-mu or the anti-delta antibody, but these stimuli were insufficient for induction of terminal plasma cell differentiation.