The B-cell binding site on human immunoglobulin E

Abstract
IMMUNOGLOBULIN E comprises the main immunoglobulin class associated with allergy. Its multifarious activities are mediated by two types of Fc receptors found on different cell populations, FcσRl on mast cells and basophils1, and FcσR2 on inflammatory cells (monocytes, eosinophils and platelets2) and B lymphocytes3. Recombinant σ-chain fragments synthesized in Escherichia coli have provided the means of mapping the receptor-binding sites on human IgE, and blocking IgE-receptor interactions. We have previously shown that the FceRl binding site is contained within a sequence (Gin 301–Arg 376) spanning the Cσ2 and Cσ3 domains4. Here we show that FcσR2 can recognize a motif in the Cσ3 domain that is formed on dimerization of one or both of the flanking (Cσ2 and Cσ4) domains. Glycosylation of IgE is not required for the activity of either receptor.