FcαRI-positive liver Kupffer cells:: Reappraisal of the function of immunoglobulin A in immunity

Despite the well-recognized involvement of immunoglobulin (Ig) A in mucosal immunity, the function of its receptor, Fc alpha RI (CD89), is poorly understood. The ability of Fc alpha RI to activate leukocytes seems to conflict with the proposed anti-inflammatory activity of secretory IgA. We show here that in a transgenic mouse model, inflammatory mediators induced expression of Fc alpha RI on Kupffer cells, which enabled efficient phagocytosis in vivo of bacteria coated with serum IgA. Secretory IgA did not initiate phagocytosis. Therefore, interactions between serum IgA and Fc alpha RI on Kupffer cells may provide a 'second line of defense' in mucosal immunity, by eliminating invasive bacteria entering through the portal circulation and thus preventing disease.