Phagocytosis of IgA Immune Complexes by Human U937 Cells

In order to study FcαRⅠ mediated phagocytosis of IgA immune complexes by U937 cells, antigen 8.9NIP/BSA was labeled with FITC and reacted with anti-NIP IgA or anti-NIP IgG antibody to form immune complexes (ICs). They were then incubated with phorbol 12-myristate 13-acetate (PMA) stimulated U937 cells.The phagocytosed ICs were quantified by flow cytometry. The results was that the expression of FcαRⅠ on U937 cells was higher than that of FcγRⅠ, FcγRⅡ and FcγRⅢ. After stimulation by PMA, expression of FcαRⅠ on U937 cells was markedly upregulated and the phagocytosis of IgA ICs was enhanced. FcαRⅠ mediated specific IgA phagocytosis was stronger than FcγRⅠ and FcγRⅡ mediated IgG phagocytosis. Complement receptors, CR1 and CR3, enhanced U937 cell phagocytosis of IgA ICs. It concludes that FcαRⅠ mediated strong phagocytosis of IgA ICs.