CD23 AND CD21 FUNCTION AS ADHESION MOLECULES IN HOMOTYPIC AGGREGATIONOF HUMAN B-LYMPHOCYTES

We have previously found that interleukin-4 and CD40 monoclonal antibo dies (mAb) are strong potentiatiors of homotypic B cell aggregation wh ich is dependent on LFA-1. We show here that CD23 mAb were also able t o inhibit aggregation to a similar extent as LFA-1 antibodies. This in hibition was restricted to the MHM6 epitope of CD23 and antibodies to other epitopes [Epstein-Barr virus (EBV) CS-1, EBV CS-2, EBV CS-5 and mAb 25] or occupation of the Fc-binding site by IgE had no or a slight ly enhancing effect on aggregation.When testing two antibodies to CD21 , the recently defined ligand for CD23, one of these (BU32) was found to be inhibitory whereas the other (THB5) had no effect. By combining antibodies to LFA-1 and CD23, aggregation was often completely inhibit ed. These data suggest that LFA-1/ICAM-1 and CD23/CD21 are the major m olecules involved in homotypic aggregation of human B cells.