CD23 REGULATES MONOCYTE ACTIVATION THROUGH A NOVEL INTERACTION WITH THE ADHESION MOLECULES CD11B-CD18 AND CD11C-CD18

CD23 is expressed on a variety of haemopoietic cells and displays plei otropic activities in vitro. We report that in addition to CD21 and Ig E, CD23 interacts specifically with the CD11b and CD11c, the alpha cha ins of the beta 2 integrin adhesion molecule complexes CD11b-CD18 and CD11c-CD18, on monocytes. Full-length recombinant CD23 incorporated in to fluorescent liposomes was shown to bind to COS cells transfected wi th cDNA encoding either CD11b-CD18 or CD11c-CD18 but not with CD11a-CD 18, The interactio n was specifically inhibited by anti-CD11b or anti- CD11c, respectively, and by anti-CD23 MAbs. The functional significanc e of this ligand pairing was demonstrated by triggering CD11b and CD11 e on monocytes with either recombinant CD23 or anti-CD11b and anti-CD1 1c MAbs to cause a marked increase in nitrite-oxidative products and p roinflammatory cytokines (IL-1 beta, IL-6, and TNF alpha). These CD23- mediated activities were decreased by Fab fragments of MAbs to CD11b, CD11c, and CD23. These results demonstrate that CD11b and CD11c are re ceptors for CD23 and that this novel ligand pairing regulates importan t activities of monocytes.