IL4 is not required for proliferative responses in B cells stimulated by anti-IgD-dextran conjugates even under limiting conditions of cell-cell interaction.

The experiments in this manuscript confirm and extend our previous finding that IL4 has minimal enhancing activity on B cell activation stimulated by anti-Ig-dextran conjugates. The absence of significant IL4-mediated enhancement is seen also under conditions which are limiting for optimal B cell proliferation. Thus, even when B cells are cultured at low cell densities where cell to cell contact is minimized and are stimulated with picogram per milliliter concentrations of anti-Ig-dextran, IL4 mediates low levels of enhanced proliferation, if at all. The low level of IL4-induced enhancement does not reflect the anti-Ig-dextran-mediated downregulation of IL4 receptors on B cells, since anti-Ig-dextran stimulates an increase in IL4 receptors similar in magnitude to that stimulated by IL4 by itself. To exclude the possibility that anti-Ig-dextran was stimulating IL4 secretion by B cells and thus masking an effect of added IL4, we added inhibiting concentrations of monoclonal anti-IL4 antibody, with the B cells and found that it was without effect on anti-Ig-dextran-stimulated proliferation. Our results suggest that IL4 may not have a prominent role in influencing B cell growth that is stimulated by multivalent T cell-independent antigens.