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Moculating effect of the late-acting components of the complement system on the bactericidal activity of human
Abstract:
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 C9 nature of the killing factor in the PMN homogenate was ruled out by its inability to lyse EAC1-8 and by the finding that the killing of BAC1-8 by the PMN factor was not inhibited by the antiserum against human C9. 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.
Insights
Complement components influence bacterial killing by human neutrophils. Specifically, complement component 8 (C8) plays a crucial role in the intracellular killing of E. coli 0111:B4 by PMNs.
Area of Science:
- Immunology
- Microbiology
Background:
- The complement system is a critical part of innate immunity.
- Neutrophils (PMNs) are key phagocytic cells involved in bacterial clearance.
- Understanding complement's role in PMN-mediated bacterial killing is essential for immune research.
Purpose of the Study:
- To investigate the specific effects of complement (C) components on the intracellular killing of E. coli 0111:B4 by human PMNs.
- To identify which complement components are essential for this killing mechanism.
Main Methods:
- Opsonization of E. coli 0111:B4 with various complement-deficient sera and purified components.
- Phagocytosis assays using human PMNs and bacterial preparations.
- Intracellular killing assays using intact PMNs and PMN homogenates (postnuclear supernatant).
- Inhibition assays using antisera against specific complement components (C5, C8, C9).
Main Results:
- Human PMNs phagocytosed all prepared bacterial strains.
- Intracellular killing was most effective for bacteria opsonized with partially purified C8 (BAC1-8) and, to a lesser extent, with C6-deficient serum (BAC1-5).
- Similar killing patterns were observed using PMN homogenates, indicating an intracellular mechanism.
- The killing factor was not complement component 9 (C9) and did not require bound C5 or C8 for its activity.
Conclusions:
- Complement component 8 (C8) is important for the efficient intracellular killing of E. coli 0111:B4 by human PMNs.
- The intracellular killing mechanism involves factors within the PMN homogenate and is not directly mediated by C9.
- Bound C5 and C8 do not appear to serve as binding sites for the identified intracellular killing factor.