IgE receptor on human eosinophils (FcERII). Comparison with B cell CD23 and association with an adhesion molecule

IgE FcR (FcERII) on human eosinophils was characterized and compared with FcERII present on B cells (CD23). Two mAb, BB10 (anti-eosinophil FcERII) and 135 (anti-CD23), bound to the major component of FcERII at 45,000 to 50,000 Mr, both on purified hypodense eosinophils and on a B cell line (WIL-2WT). The specific ligand, human myeloma IgE, was able to bind to the molecules immunoprecipitated by BB10. A cross-reactivity between BB10 and a mAb anti-Leishmania gp63, which is a "fibronectin (Fn)-like" molecule, containing the L-arginine-L-glycyl-L-aspartyl (RGD) cell attachment domain indicated the presence of such a sequence in the common structure present on eosinophil and B cell FcERII. The synthetic tetrapeptide RGDS as well as its inverted sequence (SDGR) reduced the binding of BB10 and anti-Fn mAb to eosinophils and B cells. Flow microfluorometry analysis revealed a variable binding of BB10 and anti-Fn mAb to eosinophils purified from different patients, results compatible with recent findings on the inducibility of FcERIIb. The significant inhibition of IgE-dependent cytotoxicity against parasite targets by preincubation of eosinophils with BB10, anti-Fn and anti-CD23 mAb, with anti-RGDS polyclonal antibodies or with the SDGR peptide suggested the requirement of this cell adhesion sequence for the function of low affinity FcERII. The presence of such a sequence in the C-terminal domain of B cell FcERII raised the possibility of its role in B cell adhesion or B cell growth.