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Protective and heart-crossreactive epitopes located within the NH2 terminus of type 19 streptococcal M protein
M S Bronze1, E H Beachey, J B Dale
1Veterans Administration Medical Center, Memphis, Tennessee.
Abstract:
M protein was purified to homogeneity from limited pepsin digests of intact type 19 streptococci (pep M19). The purified pep M19 when emulsified in CFA and injected into rabbits evoked type-specific and crossreactive opsonic antibodies, as well as heart-crossreactive antibodies. The NH2-terminal primary structure of pep M19 was determined and a peptide copying the first 24 amino acids [SM19(1-24)C] was chemically synthesized. Rabbits that were immunized with the unconjugated peptide developed antibodies that recognized the native pep M19, as determined by ELISA, and opsonic antibodies against type 19 streptococci, as determined by in vitro opsonophagocytosis tests. The synthetic peptide also evoked antibodies that crossreacted with a 60-kD sarcolemmal membrane protein of human myocardium. By using overlapping synthetic subpeptides as immunoinhibitors, the opsonic and heart-crossreactive epitopes of SM19(1-24)C were localized to SM19(11-24)C. Our data confirm the presence of heart-crossreactive epitopes within the primary structure of pep M19 and show that these potentially harmful autoimmune epitopes may be located in the NH2-terminal regions of certain M proteins. We conclude that continued efforts to identify the primary structures of protective and heart-crossreactive epitopes will be necessary to elucidate the pathogenesis of acute rheumatic heart disease and to develop safe and effective streptococcal vaccines.
Insights
Researchers identified heart-crossreactive epitopes in M protein from type 19 streptococci. These findings are crucial for understanding rheumatic heart disease and developing safer streptococcal vaccines.
Area of Science:
- Immunology
- Microbiology
- Molecular Biology
Background:
- Streptococcus pyogenes M proteins are key virulence factors.
- Some M proteins elicit antibodies that cross-react with heart tissue, potentially contributing to rheumatic heart disease.
- Understanding the structure of these epitopes is vital for vaccine development.
Purpose of the Study:
- To investigate the presence and location of heart-crossreactive epitopes within the M protein of type 19 Streptococcus.
- To synthesize and immunize with a peptide representing the N-terminus of M19 protein to assess antibody responses.
- To identify specific regions within the M19 N-terminus responsible for opsonic and heart-crossreactive antibody generation.
Main Methods:
- Purification of M protein (pep M19) from type 19 streptococci.
- Chemical synthesis of an N-terminal peptide fragment [SM19(1-24)C].
- Immunization of rabbits with purified pep M19 and synthetic peptide, followed by antibody analysis (ELISA, opsonophagocytosis assays) and epitope mapping using overlapping subpeptides.
Main Results:
- Purified pep M19 elicited type-specific, cross-reactive opsonic, and heart-crossreactive antibodies.
- The synthetic N-terminal peptide SM19(1-24)C induced antibodies recognizing native M19 and providing opsonophagocytosis against type 19 streptococci.
- Antibodies generated by the synthetic peptide also cross-reacted with human heart sarcolemmal proteins.
- Epitope mapping localized both opsonic and heart-crossreactive epitopes to the SM19(11-24)C subpeptide.
Conclusions:
- Heart-crossreactive epitopes are present in the N-terminal region of type 19 M protein.
- These potentially autoimmune epitopes are located within the SM19(11-24)C sequence.
- Further research into protective and cross-reactive epitope structures is essential for elucidating rheumatic heart disease pathogenesis and creating effective, safe streptococcal vaccines.