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Nucleotide sequence and T cell epitopes of a membrane protein of Francisella tularensis
A Sjöstedt1, G Sandström, A Tärnvik
1Department of Cell- and Microbiology, National Defence Research Establishment, Umeå, Sweden.
Abstract:
A 17-kDa major membrane protein of the facultative intracellular bacterium Francisella tularensis is recognized by T cells from individuals previously undergoing tularemia or tularemia vaccination. Here the nucleotide sequence of the encoding gene is presented. The A + T rich sequence deduced a protein of 149 amino acids with a predicted m.w. of 15,772. Evidence is presented suggesting that the 17-kDa protein is a lipoprotein. Also, homology was found to a peptidoglycan-associated lipoprotein of Escherichia coli. Thirteen overlapping synthetic peptides encompassing the entire deduced protein were tested on lymphocytes from F. tularensis-primed individuals. Three peptides induced a T cell response, as disclosed by lymphocyte proliferation and production of IL-2 and IFN-gamma. Out of five responding individuals, only one recognized more than one of the peptides. A murine mAb recognized an epitope separate from the T cell-reactive peptides. The identified T cell epitopes are presumably relevant to the host defense against F. tularensis, especially because IFN-gamma is known to enhance the antimicrobial activity of the host against intracellular bacteria.
Insights
Researchers identified key T cell epitopes on a major 17-kDa membrane protein of Francisella tularensis. These findings are crucial for understanding host defense against tularemia and developing effective vaccines.
Area of Science:
- Immunology
- Microbiology
- Bacterial Pathogenesis
Background:
- Francisella tularensis is a facultative intracellular bacterium causing tularemia.
- A 17-kDa major membrane protein is recognized by T cells in individuals with prior tularemia or vaccination.
- Understanding immune responses to F. tularensis is critical for developing effective countermeasures.
Purpose of the Study:
- To present the nucleotide sequence of the gene encoding the 17-kDa F. tularensis protein.
- To characterize the 17-kDa protein, including its potential lipoprotein nature and homology to other bacterial proteins.
- To identify specific T cell epitopes within the 17-kDa protein relevant to host immunity.
Main Methods:
- Gene sequencing and protein analysis (deduced amino acid sequence, molecular weight).
- Investigation of protein characteristics, including potential lipoprotein nature and homology searches.
- Synthesis and testing of overlapping peptides derived from the protein on lymphocytes from primed individuals.
- Measurement of lymphocyte proliferation and cytokine production (IL-2, IFN-gamma).
- Epitope mapping using a murine monoclonal antibody (mAb).
Main Results:
- The gene sequence was determined, predicting a 149-amino acid protein (15,772 Da).
- Evidence suggests the protein is a lipoprotein, showing homology to E. coli peptidoglycan-associated lipoprotein.
- Three synthetic peptides elicited T cell responses (proliferation, IL-2, IFN-gamma production) in F. tularensis-primed individuals.
- T cell recognition was largely peptide-specific, with limited cross-reactivity among individuals.
- A murine mAb recognized an epitope distinct from the T cell-reactive sites.
Conclusions:
- The identified T cell epitopes on the 17-kDa protein are likely important for host defense against F. tularensis.
- Interferon-gamma (IFN-gamma) production, induced by these epitopes, enhances the host's antimicrobial activity against intracellular bacteria.
- These findings provide insights into T cell-mediated immunity against tularemia and potential targets for vaccine development.