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Published on: March 8, 2012
Direct sequence identification and kinetic analysis of an MHC class I-restricted Listeria monocytogenes CTL epitope
1Infectious Diseases Section, Yale University School of Medicine, New Haven, CT 06510.
Insights
Researchers identified a new bacterial peptide epitope, p60 217-225, from Listeria monocytogenes using direct MHC analysis. This finding aids in understanding the immune response to intracellular bacterial infections.
Area of Science:
- Immunology
- Microbiology
- Molecular Biology
Background:
- Intracellular bacterial infections like Listeria monocytogenes trigger MHC class I-restricted T-cell responses.
- Identifying pathogen-specific epitopes among abundant self-peptides presented by MHC molecules is challenging.
Purpose of the Study:
- To determine the sequence of a pathogen-derived T-cell receptor epitope by direct analysis of peptides from MHC class I molecules.
- To characterize the kinetics and quantity of a novel Listeria monocytogenes epitope during infection.
Main Methods:
- Direct sequencing of peptides extracted from MHC class I molecules in infected murine models.
- Quantitation of specific bacterial epitopes (p60 217-225 and listeriolysin 91-99) within infected cells over time.
Main Results:
- A novel CTL epitope, p60 217-225, derived from the secreted protein p60, was identified and sequenced.
- This epitope is presented by the H-2Kd MHC class I molecule and is rapidly detectable (within 2 hours) and abundant (over 3000 copies/cell at 9 hours).
- Compared to listeriolysin 91-99, the p60 epitope exhibits significantly faster kinetics and higher abundance during infection.
Conclusions:
- Direct sequencing of MHC-bound peptides is a feasible method for identifying novel T-cell epitopes.
- Kinetic and quantitative analysis of T-cell epitopes provides valuable insights into the multispecific CTL response against intracellular pathogens.
Abstract:
Murine infection with the intracellular bacterium Listeria monocytogenes elicits MHC class I-restricted CTL with specificity for multiple bacterial peptides. The variety and relative abundance of self-peptides bound by MHC molecules make identification of pathogen-derived peptides difficult. In this report, the sequence of a pathogen-derived CTL epitope is determined by direct analysis of peptides extracted from MHC class I molecules. The epitope, p60 217-225, is presented to L. monocytogenes-specific CTL by the H-2Kd MHC class I molecule and is derived from p60, a secreted invasion-associated protein. Quantitation of p60 217-225 in infected cells shows that this epitope is detectable within 2 h of infection and, after a 9-h infection, there are over 3000 epitopes per infected cell. This contrasts with listeriolysin 91-99, the other major L. monocytogenes epitope, which is present in quantities below 200 epitopes per cell until 5 h of infection and reaches 800 epitopes per cell 9 h after infection. This report shows that identifying new T lymphocyte epitopes by direct sequence analysis of peptides isolated from MHC molecules is feasible. Furthermore, kinetic and quantitative analysis of T cell epitopes in infected cells is a useful approach to investigate the multispecific CTL response to complex intracellular pathogens.
