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Antigenicity of the M proteins of group A hemolytic streptococci: further evidence for shared determinants among
Abstract:
Shared antigenic determinants between M proteins of group A streptococci appear to be widespread among serotypes. This is demonstrated by the ability of purified M proteins to absorb opsonic antibody from a variety of heterologous antisera prepared against whole cells or purified M proteins. This absorption procedure has the capacity to separate passive mouse protecting and passive hemagglutinating antibodies from opsonic antibodies measured in vitro. When whole cells or M proteins are used as heterologous absorbents, immunoglobulin may be recovered from the cells or precipitates. The recovered antibody has most of the opsonic and some of the precipitating qualities of the original unabsorbed serum, but hemagglutinating titers are significantly lower. These data provide additional evidence that shared antigenicity among M proteins can be the result of common antigenic determinants. Arguments are presented that these cross-reactions are not the result of a nonspecific protein fraction associated with purified M proteins.
Insights
Shared antigenic determinants in M proteins of group A streptococci are common. Antibodies absorbed with M proteins retain opsonic activity, indicating shared epitopes across serotypes.
Area of Science:
- Microbiology
- Immunology
- Bacteriology
Background:
- M proteins are key virulence factors of group A streptococci.
- Serotype diversity of M proteins complicates vaccine development.
- Shared antigenic determinants among M proteins have been suggested but not fully characterized.
Purpose of the Study:
- To investigate the extent and nature of shared antigenic determinants among M proteins of group A streptococci.
- To determine if these shared determinants elicit opsonic antibodies.
- To differentiate between opsonic and other antibody activities (passive mouse protection, hemagglutination).
Main Methods:
- Purified M proteins and whole cells of group A streptococci were used as absorbents.
- Heterologous antisera were absorbed with these preparations.
- Antibody activity (opsonic, passive mouse protection, hemagglutination) was measured before and after absorption.
- Immunoglobulin was recovered from precipitates and its activity assessed.
Main Results:
- Purified M proteins effectively absorbed opsonic antibodies from heterologous antisera, indicating shared epitopes.
- Absorption procedures could separate opsonic antibodies from passive mouse protecting and hemagglutinating antibodies.
- Recovered antibodies retained significant opsonic and precipitating qualities, but hemagglutinating titers were reduced.
- Evidence suggests shared antigenicity is due to common antigenic determinants, not nonspecific protein fractions.
Conclusions:
- Shared antigenic determinants are widespread among M proteins of group A streptococci.
- These shared determinants are recognized by opsonic antibodies.
- Understanding these shared epitopes is crucial for developing broadly protective vaccines against group A streptococci.