STRUCTURE AND FUNCTION OF HUMAN-IGA FC-RECEPTORS (FC-ALPHA-R)

Receptors for the Fc region of IgA are expressed by many human cell ty pes, especially phagocytes located in mucosal areas, where IgA is the prevalent antibody isotype. Binding of IgA-opsonized particles (e.g., bacteria, viruses) to Fc alpha R may trigger a plethora of cell-mediat ed immune effector functions designed to rid the body of the foreign i nvader. The IgA receptor present on myeloid cells such as neutrophils, eosinophils, and monocytes (Fc alpha RI or CD89) is a transmembrane g lycoprotein that binds both IgA isotypes with similar affinity. Geneti c characterization showed Fc alpha RI to be a more distantly related m ember of the Ig receptor gene family. Recently, Fc alpha RI was found to associate with the FcR gamma-chain signaling molecule through a uni que charge-based mechanism. Fc alpha RI is, thus, connected to the int racellular machinery via the ITAM signaling motifs located within the cytoplasmic tail of FcR gamma-chain. Evidence exists in support of rec eptors for IgA (distinct from Fc alpha RI) on human T and B cells. IgA Fc receptors may, therefore, play a role in both the induction and co ntrol of an efficient (mucosal) immune response.