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Updated: Aug 5, 2026
Peptide:MHC Tetramer-based Enrichment of Epitope-specific T cells
Published on: October 22, 2012
Two T cell epitopes from the M5 protein of viable Streptococcus pyogenes engage different pathways of bacterial
1Department of Immunology, The Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom.
Abstract:
We studied the mechanisms of MHC class II-restricted bacterial Ag processing of the surface fibrillar M5 protein from viable Streptococcus pyogenes in murine macrophages. Two previously defined T cell epitopes were studied using T cell hybridomas specific for 308-319/Ad, associated with the cell wall on the surface of streptococci, and 17-31/Ed, located at the protruding amino terminus of M5. Studies with metabolic inhibitors showed that slow (1 h) processing of M5 308-319 occurred in late endosomes and was dependent on newly synthesized MHC class II molecules and microtubules and on communications between early and late endosomes, consistent with engagement of the classical MHC class II processing pathway. In contrast, fast (15 min) bacterial Ag processing of 17-31 occurred in early endosomes independently of newly synthesized MHC class II molecules and microtubules and of trafficking between early and late endosomes, consistent with the recycling MHC class II processing pathway. Finally, bacterial Ag processing of the epitopes exhibited differential sensitivity to blocking with anti-MHC class II Abs. Thus, two T cell epitopes of a single protective Ag from the surface of whole bacteria are routed to distinct MHC class II processing pathways.
Insights
Two T cell epitopes from Streptococcus pyogenes M5 protein utilize distinct Major Histocompatibility Complex (MHC) class II processing pathways in macrophages. One pathway involves late endosomes and new MHC class II, while the other uses early endosomes and recycling MHC class II.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Streptococcus pyogenes M5 protein is a key target for T cell immunity.
- Understanding antigen processing is crucial for vaccine development.
Purpose of the Study:
- To investigate the distinct intracellular processing pathways for two T cell epitopes of the M5 protein in murine macrophages.
- To elucidate the roles of endosomal compartments and MHC class II molecules in antigen processing.
Main Methods:
- Utilized T cell hybridomas specific for M5 epitopes.
- Employed metabolic inhibitors to study processing kinetics and pathways.
- Investigated the dependence on de novo MHC class II synthesis, microtubules, and endosomal trafficking.
- Assessed the impact of anti-MHC class II antibodies on antigen processing.
Main Results:
- The M5 308-319 epitope followed a slow processing pathway in late endosomes, dependent on new MHC class II and microtubules.
- The M5 17-31 epitope underwent fast processing in early endosomes, independent of new MHC class II and microtubules.
- Differential sensitivity to anti-MHC class II antibodies was observed for the two epitopes.
Conclusions:
- Two epitopes from the same bacterial antigen are processed via distinct Major Histocompatibility Complex (MHC) class II pathways.
- These findings highlight the flexibility of antigen processing and presentation by macrophages.
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