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Type-specific inhibition of preopsonization versus immunoprecipitation by Streptococcal M proteins
Abstract:
Purified M protein of group A streptococci inhibits in vitro phagocytosis of bacteria nonspecifically when it is mixed directly with the test blood. We devised a method of preopsonization inhibition that avoids direct contact between the test blood and the opsonic inhibitory agent. Each of the M proteins tested by this method inhibited opsonization and phagocytosis of only homologous-type streptococci. Titration of the M antigen in various purified preparations demonstrated a clear dissociation between titers of type-specific precipitating M antigen and type-specific opsonic inhibitory M antigen. Since opsonization reflects protective antibody, assays of M protein based on reaction with opsonic antibody should reflect more accurately the presence of the type-specific M determinant involved in protective immunity against streptococcal infections.
Insights
Group A Streptococcus M protein can hinder bacterial engulfment. A new method shows M protein specifically inhibits opsonization and phagocytosis only for its matching bacterial type, revealing its role in protective immunity.
Area of Science:
- Microbiology
- Immunology
- Bacteriology
Background:
- Group A Streptococcus (GAS) M protein is a key virulence factor.
- Nonspecific inhibition of phagocytosis by M protein complicates immune studies.
- Accurate assessment of M protein's role in immunity is crucial.
Purpose of the Study:
- To develop a method to specifically assess M protein's inhibitory effect on opsonization and phagocytosis.
- To differentiate between nonspecific and type-specific inhibition by M protein.
- To correlate M protein's opsonic inhibitory activity with protective immunity.
Main Methods:
- Devised a preopsonization inhibition assay to prevent direct contact between M protein and test blood.
- Tested purified M proteins from various GAS serotypes.
- Titrated M antigen and measured opsonic inhibitory activity.
Main Results:
- Preopsonization inhibition assay demonstrated type-specific inhibition of opsonization and phagocytosis by M protein.
- Dissociation observed between titers of precipitating M antigen and opsonic inhibitory M antigen.
- Opsonic inhibitory activity correlated with type-specific protective immunity.
Conclusions:
- M protein exhibits type-specific inhibition of opsonization and phagocytosis when direct contact with blood is avoided.
- Assays measuring reaction with opsonic antibody provide a more accurate measure of protective M protein determinants.
- This method enhances understanding of M protein's role in streptococcal immunity.