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Identification of an H2-M3-restricted Listeria epitope: implications for antigen presentation by M3
1Department of Immunology, University of Washington, Seattle, 98195, USA.
Abstract:
Using expression cloning, we have identified an H2-M3-restricted epitope of the intracellular bacterial pathogen Listeria monocytogenes. Picomolar concentrations of an amino-terminal N-formylated hexapeptide, fMIGWII, targeted cells for lysis by CD8+ cytotoxic T cells, while the nonformylated peptide was approximately 100-fold less active. The sequence of the 185 aa protein source of this epitope predicts a transmembrane protein that retains its N terminus and assumes an N(out)-C(in) topology. This membrane orientation offers an explanation for the protection of the epitope from deformylases present in the bacterial cell and suggests an explanation for the ability of phagocytes to present H2-M3-restricted bacterial epitopes via a vacuolar TAP-independent mechanism.
Insights
Researchers identified a specific peptide from Listeria monocytogenes that effectively triggers CD8+ cytotoxic T cells. This N-formylated hexapeptide is crucial for immune response against this intracellular bacterial pathogen.
Area of Science:
- Immunology
- Microbiology
- Molecular Biology
Background:
- Intracellular bacterial pathogens like Listeria monocytogenes pose significant challenges to the host immune system.
- Understanding the mechanisms of antigen presentation is key to developing effective immune responses.
Purpose of the Study:
- To identify and characterize a specific epitope from Listeria monocytogenes recognized by H2-M3 restricted T cells.
- To elucidate the role of peptide formylation in T cell activation and antigen presentation.
Main Methods:
- Expression cloning was employed to identify the H2-M3-restricted epitope.
- Synthetic peptides, including an N-formylated hexapeptide (fMIGWII), were synthesized and tested for T cell activation.
- Bioinformatic analysis of the epitope's source protein sequence and predicted membrane topology.
Main Results:
- An N-formylated hexapeptide, fMIGWII, from Listeria monocytogenes was identified as a potent H2-M3-restricted epitope.
- Picomolar concentrations of the formylated peptide induced significant CD8+ cytotoxic T cell lysis.
- The non-formylated peptide showed a 100-fold lower activity, highlighting the importance of N-formylation.
- The epitope originates from a predicted transmembrane protein with an N(out)-C(in) topology, protecting it from bacterial deformylases.
Conclusions:
- The N-formylated hexapeptide fMIGWII is a critical determinant for H2-M3-restricted CD8+ T cell recognition of Listeria monocytogenes.
- The unique membrane topology of the epitope's source protein explains its protection from bacterial enzymes and suggests a vacuolar, TAP-independent antigen presentation pathway in phagocytes.