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Location of variable and conserved epitopes among the multiple serotypes of streptococcal M protein
Abstract:
In studies primarily confined to the amino-terminal region of the fibrillar group A streptococcal M protein, only limited immunological crossreactions have been observed among M serotypes. In this investigation, two monoclonal antibodies generated against nearly the entire M6 molecule (LysM6) were used to determine the extent of crossreactions among M serotyping strains and to localize their epitopes on the M molecule. Colony blot and immunoblot analyses revealed that an epitope responsible for crossreactions among 5 of the 56 strains of different M serotypes tested is located in the amino-terminal half of the molecule, distal to the cell surface. In contrast, a more common crossreactive epitope, reacting with 20 of the 56 strains, is located near the middle of the M molecule. These studies also reveal that the more conserved determinant, located more proximally to the cell surface, is accessible to the immune system, even on the whole organism, and, thus, may be useful in devising means to protect against infections by multiple group A streptococcal M serotypes.
Insights
This study mapped crossreactive epitopes on group A streptococcal M protein. A conserved epitope near the M molecule
Area of Science:
- Microbiology
- Immunology
- Protein Chemistry
Background:
- Previous studies on group A streptococcal M protein focused on the amino-terminal region, showing limited serotype cross-reactivity.
- Understanding M protein epitopes is crucial for developing broad-spectrum vaccines against streptococcal infections.
Purpose of the Study:
- To determine the crossreactivity extent among different M serotypes using monoclonal antibodies against the M6 protein.
- To localize the specific epitopes responsible for these crossreactions on the M protein molecule.
Main Methods:
- Generation of two monoclonal antibodies (LysM6) against the M6 protein.
- Colony blot and immunoblot analyses to assess antibody binding to various M serotypes.
Main Results:
- An epitope in the amino-terminal half of the M6 molecule, distal to the cell surface, crossreacted with 5 out of 56 strains.
- A more common crossreactive epitope, located near the middle of the M molecule, reacted with 20 out of 56 strains.
- A conserved epitope, proximal to the cell surface, was accessible on the whole organism.
Conclusions:
- Two distinct crossreactive epitopes on the group A streptococcal M protein have been identified and localized.
- The conserved, cell-surface-proximal epitope shows potential for developing vaccines targeting multiple M serotypes.