Two Listeria monocytogenes CTL epitopes are processed from the same antigen with different efficiencies

Area of Science:

• Immunology
• Microbiology
• Molecular Biology

Background:

• Listeria monocytogenes infection triggers MHC class I-restricted cytotoxic T lymphocyte (CTL) responses in mice.
• A key CTL epitope is the p60 217-225 peptide from bacterial murein hydrolase p60, presented by H-2Kd.
• Understanding antigen processing and presentation is crucial for vaccine development and immunotherapy.

Purpose of the Study:

• To identify and characterize additional H-2Kd-presented CTL epitopes derived from Listeria monocytogenes p60.
• To compare the processing efficiency and natural abundance of different p60-derived epitopes.
• To investigate the factors influencing antigen processing and CTL epitope presentation.

Main Methods:

• Identification of naturally processed peptides eluted from Listeria monocytogenes-infected macrophages.
• Characterization of CTL responses using specific T-cell clones (e.g., WP11.12).
• Quantitative analysis of epitope abundance and competition assays for MHC binding and TAP transport.

Main Results:

• A second H-2Kd-presented CTL epitope, p60 449-457, was identified from Listeria monocytogenes.
• Both p60 449-457 and p60 217-225 efficiently bind H-2Kd and are transported by TAP.
• The natural abundance of p60 449-457 in infected cells is approximately 10-fold higher than p60 217-225.
• Altering the position of p60 217-225 reduced its processing efficiency, suggesting intrinsic factors influence processing.

Conclusions:

• Antigen processing efficiency and kinetics can vary significantly even for epitopes derived from the same antigen and presented by the same MHC molecule.
• The location and intrinsic properties of a peptide within a protein are critical determinants of its processing and presentation as a CTL epitope.
• These findings provide insights into the mechanisms governing T-cell epitope generation and immune recognition during bacterial infections.