Human anti-peptidoglycan-IgG-mediated opsonophagocytosis is controlled by calcium mobilization in phorbol myristate acetate-treated U937 cells

Recently, we demonstrated that human serum amyloid P component (SAP) specifically recognizes exposed bacterial peptidoglycan (PGN) of wall teichoic acid (WTA)-deficient Staphylococcus aureus Delta tagO mutant cells and then induces complement-independent phagocytosis. In our preliminary experiments, we found the existence of human serum immunoglobulins that recognize S. aureus PGN (anti-PGN-IgGs), which may be involved in complement-dependent opsonophagocytosis against infected S. aureus cells. We assumed that purified serum anti-PGN-IgGs and S. aureus Delta tagO mutant cells are good tools to study the molecular mechanism of anti-PGN-IgG-mediated phagocytosis. Therefore, we tried to identify the intracellular molecule(s) that is involved in the anti-PGN-IgG-mediated phagocytosis using purified human serum anti-PGN-IgGs and different S. aureus mutant cells. Here, we show that anti-PGN-IgG-mediated phagocytosis in phorbol myristate acetate-treated U937 cells is mediated by Ca2+ release from intracellular Ca2+ stores and anti-PGN-IgG-dependent Ca2+ mobilization is controlled via a phospholipase C gamma-2-mediated pathway.