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 with CD40 antibodies and interleukin-4 (IL-4). This stimulation also results in homotypic aggregation and cell proliferation. We have shown previously that IgE synthesis may be dependent on additional signals provided by the close cellular contact. Thus inhibition of the aggregation by lymphocyte function-associated antigen-1 (LFA-1) antibodies leads to a decrease in IgE production. In the present study we show that the inhibitory effect of LFA-1 antibodies is critically dependent on the CD40 antibody used for stimulation. Thus, while previously using the monoclonal antibody (mAb) S2C6, IgE production induced by the CD40 antibody mAb89 was generally higher and could be enhanced more than fivefold in the presence of LFA-1 antibodies. Similarly, the addition of the CD23 mAb MHM6, which blocked aggregation to a similar degree as the LFA-1 antibodies, inhibited S2C6-induced IgE production but enhanced that induced by mAb89. In contrast to these opposing effects on IgE synthesis, 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 structures on CD21 by the lectin-like domain on CD23, we also tested the effect of some different sugars on IgE synthesis and proliferation. Addition of fucose-1-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. In contrast to the MHM6 antibody, the effect of the sugars was similar irrespective of the CD40 antibody used for stimulation. The study shows that different antibodies to CD40 may give rise to qualitatively distinct signals depending on the epitope recognized.