Alternate complement pathway activation by group A streptococci: role of M-protein

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Published on: August 19, 2016

A L Bisno

    Infection and Immunity
    |December 1, 1979
    PubMed

    Insights

    Virulent M-protein strains of Group A Streptococcus are poor activators of the alternate complement pathway (ACP). M protein may hinder ACP activation, contributing to bacterial virulence.

    Area of Science:

    • Microbiology
    • Immunology
    • Bacteriology

    Background:

    • Group A Streptococcus (GAS) is a significant human pathogen.
    • The alternate complement pathway (ACP) is crucial for innate immunity against bacterial infections.
    • M protein is a key virulence factor in GAS, associated with resistance to phagocytosis.

    Purpose of the Study:

    • To investigate the role of M protein in the activation of the alternate complement pathway (ACP) by Group A Streptococcus.
    • To elucidate the mechanism by which M protein influences complement-mediated immune responses.

    Main Methods:

    • Comparative analysis of ACP activation by virulent (M-positive) and avirulent streptococcal strains.
    • Treatment of M-positive strains with trypsin or mild peptic digestion to assess the role of M protein moieties.
    • Assessment of opsonophagocytosis in serum with blocked classic complement pathway (Mg-EGTA) versus serum deficient in heat-labile factors.

    Main Results:

    • Avirulent streptococci efficiently activate the ACP in normal human serum.
    • Virulent M-positive streptococci exhibit reduced ACP activation.
    • Trypsinization or mild peptic digestion of M-positive strains enhances ACP activation.
    • Phagocytosis of avirulent streptococci is enhanced by opsonization via the classic complement pathway, but not the ACP.

    Conclusions:

    • M protein likely functions as a virulence factor by inhibiting the interaction of ACP components with the streptococcal cell surface.
    • This inhibition of the ACP may contribute to immune evasion and pathogenesis of Group A Streptococcus infections.

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