Human intestinal epithelial cells express a novel receptor for IgA

Binding and transport of polymeric Igs (pIgA and IgM) across epithelia is m ediated by the polymeric Ig receptor (pIgR), which is expressed on the baso lateral surface of secretory epithelial cells. Although an Fc receptor for IgA (Fc alpha R) has been identified on myeloid cells and some cultured mes angial cells, the expression of an FcaR on epithelial cells has not been de scribed. In this study, binding of IgA to a human epithelial line, HT-29/19 A, with features of differentiated colonic epithelial cells, was examined. Radiolabeled monomeric IgA (mIgA) showed a dose-dependent, saturable, and c ation-independent binding to confluent monolayers of HT-29/19A cells. Exces s of unlabeled mIgA, but not IgG or IgM, competed for the mIgA binding, ind icating that the binding was IgA isotype-specific and was not mediated by t he pIgR, The lack of competition by asialoorosomucoid and the lack of requi rement for divalent cations excluded the possibility that IgA binding to HT -29/19A cells was due to the asialoglycoprotein receptor or beta-1,4-galact osyltransferase, previously described on HT-29 cells. Moreover, the Fc alph a R (CD89) protein and message were undetectable in HT-29/19A cells. FAGS a nalysis of IgA binding demonstrated two discrete populations of HT-29/19 ce lls, which bound different amounts of mIgA, IgA binding to other colon carc inoma cell lines was also demonstrated by FAGS analysis, suggesting that an IgA receptor, distinct from the pIgR, asialoglycoprotein receptor, galacto syltransferase, and CD89 is constitutively expressed on cultured human ente rocytes. The function of this novel IgA receptor in mucosal immunity remain s to be elucidated.