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Sequence of protective epitopes of streptococcal M proteins shared with cardiac sarcolemmal membranes
Abstract:
Synthetic peptide fragments spanning the entire amino acid sequence of pep M5 were used to detect epitopes cross-reactive with heart tissue components other than myosin. Heart-cross-reactive pep M5 antibodies were affinity purified by absorption to and elution from purified sarcolemmal membranes. Only one of the synthetic peptides, SM5(164-197)C, inhibited reactivity of the affinity-purified antibodies with pep M5 by ELISA. SM5(164-197)C linked to KLH evoked both opsonic and heart-cross-reactive antibodies in rabbits. In addition to type 5, the immune sera opsonized M types 6, 18, 19, and 49 streptococci. The antisera reacted strongly with isolated cardiac sarcolemmal membranes by immunofluorescence. In Western blots of cardiac tissue, the anti-SM5(164-197)C reacted with a 40 kDa protein but not with myosin. The reaction was inhibited by pep M5 and SM5(164-197)C but not by any of the other peptides spanning pep M5. The cross-reactive anti-SM5(164-197)C affinity purified on sarcolemmal membranes opsonized types 5, 6, and 19 but not type 24 streptococci. These results indicate that SM5(164-197)C contains heart-cross-reactive, opsonic epitopes that are shared among heterologous serotypes of group A streptococci.
Insights
Synthetic peptide fragments revealed shared epitopes between Group A Streptococcus and heart tissue. The peptide SM5(164-197)C contains heart-cross-reactive, opsonic epitopes shared among streptococcal serotypes.
Area of Science:
- Immunology
- Microbiology
- Cardiology
Background:
- Group A Streptococcus (GAS) infections can lead to autoimmune sequelae like rheumatic heart disease.
- Cross-reactivity between GAS antigens and host tissues, particularly heart tissue, is implicated in these autoimmune responses.
- Identifying specific GAS epitopes responsible for this cross-reactivity is crucial for understanding pathogenesis and developing interventions.
Purpose of the Study:
- To identify specific epitopes within the M5 protein of Group A Streptococcus that cross-react with human heart tissue.
- To investigate the functional significance of these cross-reactive epitopes, including their opsonic activity and potential role in autoimmune responses.
- To determine if these epitopes are shared among different serotypes of GAS.
Main Methods:
- Synthetic peptide fragments covering the entire M5 protein sequence were synthesized.
- Antibodies generated against M5 protein were affinity-purified using cardiac sarcolemmal membranes.
- Enzyme-linked immunosorbent assay (ELISA) and Western blotting were used to assess antibody reactivity.
- Immunofluorescence was employed to examine antibody binding to cardiac sarcolemmal membranes.
- Opsonization assays were performed with various GAS serotypes.
Main Results:
- A specific peptide, SM5(164-197)C, was identified as containing the primary heart-cross-reactive epitope.
- Antibodies against SM5(164-197)C reacted with a 40 kDa protein in cardiac tissue, distinct from myosin.
- Immune sera and affinity-purified antibodies showed opsonic activity against multiple GAS serotypes (types 5, 6, 18, 19, 49).
- SM5(164-197)C contains epitopes shared among heterologous serotypes of Group A Streptococcus.
Conclusions:
- The peptide SM5(164-197)C harbors critical heart-cross-reactive and opsonic epitopes.
- These epitopes are shared across different serotypes of Group A Streptococcus, suggesting a common mechanism for cross-reactivity.
- This finding has implications for understanding the autoimmune basis of heart disease following streptococcal infections and for vaccine development.