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RESEARCH PRODUCT

The role of Components of the Outer Membrane of Gram-Negative Bacteria in the Serum-Bactericidal Effect

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Abstract Effective killing-capacity of normal human and guinea pig sera depended on Ca ++ , C1q, C2 and C4. Fixation- and transfer-tests revealed that C1 and C1q were bound more tightly to the serum-sensitive R-forms of Salmonella strains than to the serum-resistant S-forms. Since all experiments were done in the absence of antibodies these findings provide evidence that the antibody-independent C1-binding is one of the initial reactions of the serum-mediated killing. This reaction seems to be influenced by the sugar-portion of the lipopolysaccharide (LPs) of the outer membrane: C1-binding to the bacteria occurs with higher affinity the shorter the LPS-molecule. This indicates that other outer membrane structures, besides LPS, such as membrane proteins are available on core-deficient mutants of gramnegative bacteria and influence the interaction with C1. A direct interaction of C1 with isolated outer membrane protein of Proteus mirabilis could already be demonstrated indicating that the outer membrane proteins serve as additional binding sites for C1.