Contributions of C1q, bacterial lipopolysaccharide, and porins during attachment and ingestion phases of phagocytosis by murine macrophages.

In contrast to the S-form of Salmonella minnesota, its Re mutant binds to mouse peritoneal macrophages. The binding reaction triggers an oxidative burst, measured by a chemiluminescent reaction. The oxidative burst was abolished in the presence of either purified lipopolysaccharide or porins (outer membrane proteins) extracted from the Re mutant, suggesting that both components are involved in binding of the Re mutant to macrophages. In addition, Fc-recognizing membrane structures on the macrophage surface bind the Re mutant. Preincubation of macrophages with the Re mutant abolishes immunoglobulin G-sensitized erythrocyte-induced chemiluminescence. Macrophages preincubated with immunoglobulin G-sensitized erythrocytes had a low chemiluminescent signal, and after treatment of the cells with the Re mutant, there was an additional, higher signal. Binding of purified C1q to the Re mutant decreased the adherence of the Re mutant to macrophages, resulting in a diminished chemiluminescent signal. Blocking of endogenous macrophage membrane-associated C1q with a monoclonal antibody [F(ab')2 fragment] directed against mouse macrophages (recognizes the A and B chains of C1q) diminished the oxidative burst. Therefore, the endogenous C1q of macrophages also appears to be involved in attachment of the S. minnesota Re mutant.