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Heterogeneity of type-specific and cross-reactive antigenic determinants within a single M protein of group A
Abstract:
The heterogeneity of a pepsin extract of type-24 M protein (pep M24) was demonstrated by absorption of type-specific and cross-reactive human antisera with M protein fragments and heterologous serotypes of M proteins, pepsin extract of type-5 M protein (pep M5) and pepsin extract of type-6 M protein (pep M6). 2 of 12 individuals immunized with pep M24 developed significant rises in antibody titers against pep M5 and pep M6, as measured by the enzyme-linked immunosorbent assay. The sam individuals also developed opsonic antibodies against type-6, but not type-5, streptococci, which suggested the development of cross-protective immunity. Inhibition studies of one of these sera with the heterologous pep M proteins showed that the cross-reactive antibodies against pep M6 could not be blocked by high concentrations of pep M24, the immunizing antigen; these antibodies could be blocked, however, by cyanogen bromide-derived peptide fragments of pep M24, which suggested that the cross-reactive antibody was raised against an inaccessible site(s) in the pep M24 molecule. Inhibition studies of type-specific immune sera with pep M24 and peptides derived therefrom indicated that the M protein molecule contained multiple distinct as well as identical type-specific antigenic determinants that are unequally distributed among the seven derived peptide fragments.
Insights
This study reveals that M protein heterogeneity influences immune responses. Specific M protein fragments can elicit cross-protective immunity against related streptococcal serotypes, highlighting potential vaccine development strategies.
Area of Science:
- Microbiology
- Immunology
- Molecular Biology
Background:
- Streptococcal M proteins are key virulence factors.
- Understanding M protein heterogeneity is crucial for vaccine development.
- Previous studies suggest M proteins possess type-specific and cross-reactive epitopes.
Purpose of the Study:
- To investigate the heterogeneity of pepsin M protein type 24 (pep M24).
- To analyze the development of cross-protective immunity against heterologous M protein serotypes.
- To identify specific antigenic determinants responsible for cross-reactivity.
Main Methods:
- Absorption assays using type-specific and cross-reactive human antisera.
- Enzyme-linked immunosorbent assay (ELISA) to measure antibody titers.
- Inhibition studies with pepsin M protein extracts and cyanogen bromide-derived peptide fragments.
Main Results:
- Pepsin M protein type 24 (pep M24) demonstrated heterogeneity when tested against various antisera and M protein extracts.
- Two of twelve individuals immunized with pep M24 developed antibodies against pep M5 and pep M6.
- These individuals also developed opsonic antibodies against type-6 streptococci, indicating cross-protective immunity.
- Cross-reactive antibodies against pep M6 were blocked by pep M24 peptide fragments, not the whole pep M24 molecule, suggesting inaccessible antigenic sites.
- Inhibition studies revealed distinct and shared type-specific antigenic determinants within the M protein molecule.
Conclusions:
- M protein heterogeneity contributes to varied immune responses.
- Specific peptide fragments of M protein can induce cross-protective immunity.
- The distribution and accessibility of antigenic determinants on M proteins are critical for eliciting broad immunity.