Inhibition of alternative complement pathway opsonization by group a streptococcal M protein

Phillip K. Peterson, David Schmeling, Paul P. Cleary, Brian J. Wilkinson, Youngki Kim, Paul G. Quie

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39 Scopus citations


Group A streptococcal M protein is known to be antiphagocytic; however, the exact basis for this property has not been established. In this study the hypothesis was tested that cell wall-associated M protein inhibits phagocytosis by interfering with bacterial opsonization. Two strains of group A Streptococcus pyogenes, CS44 (M+) and CS64 (an M variant of CS44), were radiolabeled, and after incubation in serum these organisms were exposed to human polymorphonuclear leukocytes. Phagocytosis was quantitated by measurement of leukocyte-associated radioactivity. The contributions of complement and of immunoglobulin to streptococcal opsonization were evaluated by use of serum from a variety of sources. The results revealed that the M strain was efficiently opsonized via the alternative complement pathway in a relative absence of immunoglobulins. In contrast, the M+ strain was poorly opsonized by all sera tested. These findings suggest that streptococcal M protein in some way prevents bacterial opsonization via the alternative complement pathway and that this property of M protein may partly explain its antiphagocytic characteristic.

Original languageEnglish (US)
Pages (from-to)575-585
Number of pages11
JournalJournal of Infectious Diseases
Issue number5
StatePublished - May 1979


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