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Bactericidal activity of C9-deficient human serum
P Pramoonjago1, T Kinoshita, K S Hong
1Department of Bacteriology, Osaka University Medical School, Japan.
Journal of Immunology (Baltimore, Md. : 1950)
|February 1, 1992
Summary
Human hereditary C9-deficient serum (C9DHS) effectively kills Escherichia coli and Salmonella typhimurium strains. This bactericidal activity relies on complement activation up to C8, highlighting C9-independent mechanisms in bacterial killing.
Area of Science:
- Immunology
- Microbiology
- Complement System
Background:
- The complement system is crucial for innate immunity, mediating bacterial lysis.
- Complement component 9 (C9) is the terminal component of the membrane attack complex (MAC), traditionally thought essential for lysis.
- The role of C9-independent complement pathways in bacterial killing remains less understood.
Purpose of the Study:
- To investigate the bactericidal activity of human hereditary C9-deficient serum (C9DHS) against Escherichia coli.
- To elucidate the specific complement components and pathways involved in C9DHS-mediated bacterial killing.
- To compare the efficacy of C9DHS with normal human serum (NHS) and assess resistance mechanisms.
Main Methods:
- Enzyme-linked immunosorbent assay (ELISA) to confirm absence of C9 antigen in C9DHS.
- Bactericidal assays using E. coli strain B/SM and other E. coli and Salmonella typhimurium strains.
- Inhibition assays using specific antibodies against C5, C9, and lysozyme.
- Treatment of surviving bacteria with purified C9, lysozyme, and transferrin.
Main Results:
- C9DHS exhibited dose-dependent killing of E. coli B/SM, while C7-deficient serum did not.
- Bactericidal activity of C9DHS was inhibited by anti-C5 antibody, suggesting C5 involvement.
- Anti-C9 antibody reduced NHS bactericidal activity to the level of C9DHS, indicating C9's contribution in NHS.
- Laboratory strains of E. coli and S. typhimurium were killed by C9DHS, but pathogenic strains showed resistance.
- Tris buffer enhanced susceptibility to NHS but not C9DHS in resistant strains.
Conclusions:
- Human C9-deficient serum possesses significant bactericidal activity against susceptible bacteria, independent of C9.
- Complement activation up to C8 is sufficient for bacterial lysis in certain contexts, challenging the exclusive role of the complete MAC.
- Bacterial resistance to complement, even in the presence of C9, can occur, particularly in pathogenic strains.