HLA class II-mediated aggregation is associated with the proliferation of B lymphocytes

We have studied the role of LFA-1 antigens in human B lymphocyte aggregation, proliferation, and Ig production induced by a short stimulation via class II antigens. Cell stimulation with either bacterial superantigens or anti-DR mAbs rapidly induced homotypic cell aggregation. In response to IL-4, an increase in cell proliferation and Ig production was observed only when aggregation preceded addition of IL-4. The involvement of LFA-1 molecules in class II-induced aggregation was supported as LFA-1-deficient cells or B cells incubated with anti-LFA-1/ICAM-1 mAbs failed to aggregate after stimulation. The association between aggregation and subsequent Ig production and proliferation was further supported as, after IL-4 stimulation, in both LFA-1-deficient cells and B cells incubated with anti-LFA-1 mAbs, class II-mediated signals failed to increase Ig production or cell proliferation. These data suggest that in class II-stimulated cells, LFA-1-dependent aggregation has a major role in IL-4-dependent Ig production and proliferation of B cells.