CD40 ANTIBODIES DEFINING DISTINCT EPITOPES DISPLAY QUALITATIVE DIFFERENCES IN THEIR INDUCTION OF B-CELL DIFFERENTIATION

IgE production can be obtained in vitro by stimulating B lymphocytes w ith CD40 antibodies and interleukin-4 (IL-4). This stimulation also re sults in homotypic aggregation and cell proliferation. We have shown p reviously that IgE synthesis may be dependent on additional signals pr ovided by the close cellular contact. Thus inhibition of the aggregati on by lymphocyte function-associated antigen-1 (LFA-1) antibodies lead s to a decrease in IgE production. In the present study we show that t he inhibitory effect of LFA-I antibodies is critically dependent on th e CD40 antibody used for stimulation. Thus, while previously using the monoclonal antibody (mAb) S2C6, IgE production induced by the CD40 an tibody mAb89 was generally higher and could be enhanced more than five fold in the presence of LFA-1 antibodies. Similarly, the addition of t he CD23 mAb MHM6, which blocked aggregation to a similar degree as the LFA-I antibodies, inhibited S2C6-induced IgE production but enhanced that induced by mAb89. In contrast to these opposing effects on IgE sy nthesis, proliferation induced by the two CD40 antibodies was affected similarly by the blocking antibodies. As the interaction between CD23 and CD21 has been suggested to involve recognition of carbohydrate st ructures on CD21 by the lectin-like domain on CD23, we also tested the effect of some different sugars on IgE synthesis and proliferation. A ddition of fucose-l-phosphate to anti-CD40 and IL-4-stimulated B cells completely inhibited IgE synthesis and proliferation. Inhibition was also seen with mannose-6-phosphate but not with glucose-1-phosphate. I n contrast to the MHM6 antibody, the effect of the sugars was similar irrespective of the CD40 antibody used for stimulation. The study show s that different antibodies to CD40 may give rise to qualitatively dis tinct signals depending on the epitope recognized.