Fc alpha RI-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 unde rstood. The ability of Fc alpha RI to activate leukocytes seems to conflict with the proposed anti-inflammatory activity of secretory IgA. We show her e that in a transgenic mouse model, inflammatory mediators induced expressi on of Fc alpha RI on Kupffer cells, which enabled efficient phagocytosis in vivo of bacteria coated with serum IgA. Secretory IgA did not initiate pha gocytosis. Therefore, interactions between serum IgA and Fc alpha RI on Kup ffer cells may provide a 'second line of defense' in mucosal immunity, by e liminating invasive bacteria entering through the portal circulation and th us preventing disease.