Modulating Effect of the Late-Acting Components of the Complement System on the Bactericidal Activity of Human Polymorphonuclear Leukocytes on E. coli 0111:B4

The effect of complement (C) components on the intracellular killing of E. coli 0111:B4 by human PMN was studied. Various intermediate bacteria were prepared by opsonizing IgM-coated 0111:B4 with yeast cell-treated human serum (BAC1-3), a C6-deficient human serum (BAC1-5), a C8-deficient human serum (BAC1-7), a C8-deficient human serum, and with partially purified C8 (BAC1-8). All these bacterial preparations were phagocytosed by human PMN. but only BAC1-8 and, to a lesser extent, BAC1-5 were killed. Similar results were obtained when the 400 x G postnuclear supernatant (PNS) of PMN homogenate was used instead of intact leukocytes. The anti-C5 and anti-C8 antisera were unable to inhibit the killing by the PNS of BAC1-5 and BAC1-8, respectively, suggesting that bound C5 and C8 do not provide a binding site for the killing factor.