PMID: 9551922Apr 29, 1998Paper

Expression of two different antiphagocytic M proteins by Streptococcus pyogenes of the OF+ lineage

The Journal of Immunology : Official Journal of the American Association of Immunologists
A ThernG Lindahl

Abstract

All clinical isolates of Streptococcus pyogenes (group A streptococcus) share the ability to resist phagocytosis and grow in human blood. In many strains, this property is due to the expression of a single antiphagocytic M protein, while other strains express more than one M-like molecule, of which the role in phagocytosis resistance is unclear. In particular, all S. pyogenes strains of the OF+ lineage, representing approximately half of all isolates, express two M-like proteins, Mrp and Emm, which are immunologically unrelated. These two proteins bind different ligands that have been implicated in phagocytosis resistance: Mrp binds fibrinogen and Emm binds the complement inhibitor C4BP. Using a clinical isolate of the common serotype 22, we created mutants affected in the mrp and emm genes and characterized them in phagocytosis experiments and by electron microscopy. A double mutant mrp-emm- showed strongly decreased resistance to phagocytosis, while mrp- and emm- single mutants grew well in blood. However, optimal growth required the expression of both Mrp and Emm. Experiments in which coagulation was inhibited using the specific thrombin inhibitor, hirudin, rather than heparin, indicated that Emm is more important than Mrp f...Continue Reading

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