{ "abstract": "Human tularemia is caused by infection with the intracellular bacterium Francisella tularensis. The ability of the bacterium to cause a severe pneumonic form of the disease has led to concerns in the field of biodefense and efforts to develop a vaccine. F. tularensis LVS provides partial protection against fully virulent strains, with CD4+ T cells playing a significant role in this protection, however the recognized bacterial antigens remain largely unknown. To identify these antigens, we screened MHC class II peptides presented by infected dendritic cells using mass spectrometry-based immunopeptidomics. We identified 57 MHC-II peptides from 23 different F. tularensis LVS proteins. Most of these proteins were highly expressed in the bacterial proteome. Subsequent screening for IFN-γ responses identified ten peptides as immunogenic epitopes of CD4+ T cells following immunization of mice with F. tularensis LVS, thereby revealing previously unknown specificity and breadth of the induced immune responses. Five epitopes, derived from the antigens FTL_1678, DacD, DnaK, FTL_1498, and MinD, represented the dominant epitopes that elicited a response in at least 80% of immunizations. Finally, a peptide vaccine containing these epitopes proved to be immunogenic in mice and contributed to the early control of bacterial replication following challenge with the virulent F. tularensis FSC200 strain, although this alone was insufficient to ensure complete protection. Using immunopeptidomics, we have thus identified several immunogenic CD4+ T cell epitopes and antigens of F. tularensis LVS. Beyond their potential role in the protective immune response, the identified epitopes may also enable the development of tools for characterizing antigen-specific CD4+ T cells in vaccination studies or T cell biology research. Author summary: The establishment of effective T cell-mediated immunity is essential for the elimination of infections caused by intracellular bacterial pathogens. Identifying bacterial targets for T cells is important for determining the spectrum and specificity of immune responses, developing diagnostic tools, and designing vaccines. For the intracellular bacterium Francisella tularensis, the causative agent of tularemia, knowledge of the antigens and epitopes recognized by T cells is limited. In this study, we use immunopeptidomics to identify bacterial peptides presented by MHC class II from infected dendritic cells and a mouse model of tularemia to evaluate their immunogenicity. We uncovered several immunogenic epitopes and antigens of CD4+ T cells in the F. tularensis LVS strain and evaluated the protective potential of these epitopes against infection with the virulent F. tularensis FSC200 strain. Our study provides new insights into the specificity, dominance, and breadth of CD4+ T cell immune responses induced by F. tularensis LVS.", "abstract_shown": true, "affiliations": [ "Department of Molecular Pathology and Biology, Military Faculty of Medicine, University of Defence, Hradec Kralove, Czech Republic", "Laboratory of Immunobiology, Institute of Molecular Genetics of the Czech Academy of Sciences, Prague, Czech Republic", "Laboratory of Adaptive Immunity, Institute of Molecular Genetics of the Czech Academy of Sciences, Prague, Czech Republic", "Biomedical Research Center, University Hospital Hradec Kralove, Hradec Kralove, Czech Republic", "Laboratory of Immunotherapy, Institute of Microbiology of the Czech Academy of Sciences, Prague, Czech Republic", "Department of Cell Biology, Faculty of Science, Charles University, Prague, Czech Republic" ], "article_type": "Research Article", "arxiv": null, "author_total": 13, "authors": [ { "affs": [ 0 ], "name": "Pavlina Laskova" }, { "affs": [ 1 ], "name": "Stanislava Porkertova" }, { "affs": [ 2 ], "name": "Ondrej Ballek" }, { "affs": [ 3 ], "name": "Lucie Balonova" }, { "affs": [ 4 ], "name": "Jana Pavloskova" }, { "affs": [ 5 ], "name": "Ales Neuwirth" }, { "name": "Ivona Pavkova" }, { "name": "Ivo Fabrik" }, { "name": "Pavol Lukac" }, { "name": "Luca Vannucci" }, { "name": "Dominik Filipp" }, { "name": "Jiri Stulik" }, { "name": "Marek Link" } ], "bibtex": "https://research.draconitic.com/paper/86j0areg0aqms.bib", "cited_by": 0, "doi": "10.1371/journal.ppat.1014597", "fulltext_url": "https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1014597", "id": "86j0areg0aqms", "issns": [ "1553-7374" ], "landing_url": "https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1014597", "language": null, "licence": "CC-BY-4.0", "licence_label": "CC BY 4.0", "licence_source": "journal", "licence_url": "https://creativecommons.org/licenses/by/4.0/", "metadata_licence": null, "native_subjects": [ [ "openalex", "1312|vaccines and immunoinformatics approaches" ], [ "plos", "/Biology and life sciences/Biochemistry/Proteins/Immune system proteins/Antigens" ], [ "plos", "/Biology and life sciences/Cell biology/Cellular types/Animal cells/Blood cells/White blood cells/Lymphocytes" ], [ "plos", "/Biology and life sciences/Cell biology/Cellular types/Animal cells/Blood cells/White blood cells/T helper cells" ], [ "plos", "/Biology and life sciences/Cell biology/Cellular types/Animal cells/Immune cells/White blood cells/Lymphocytes" ], [ "plos", "/Biology and life sciences/Cell biology/Cellular types/Animal cells/Immune cells/White blood cells/T helper cells" ], [ "plos", "/Biology and life sciences/Immunology/Immune cells/White blood cells/Lymphocytes" ], [ "plos", "/Biology and life sciences/Immunology/Immune cells/White blood cells/T helper cells" ], [ "plos", "/Biology and life sciences/Immunology/Immune response" ], [ "plos", "/Biology and life sciences/Immunology/Immune system proteins/Antigens" ], [ "plos", "/Biology and life sciences/Microbiology/Medical microbiology/Microbial pathogens/Bacterial pathogens/Francisella tularensis" ], [ "plos", "/Biology and life sciences/Organisms/Bacteria/Francisella" ], [ "plos", "/Biology and life sciences/Organisms/Bacteria/Francisella/Francisella tularensis" ], [ "plos", "/Biology and life sciences/Physiology/Immune physiology/Antigens" ], [ "plos", "/Medicine and health sciences/Immunology/Immune cells/White blood cells/Lymphocytes" ], [ "plos", "/Medicine and health sciences/Immunology/Immune cells/White blood cells/T helper cells" ], [ "plos", "/Medicine and health sciences/Immunology/Immune response" ], [ "plos", "/Medicine and health sciences/Immunology/Immune system proteins/Antigens" ], [ "plos", "/Medicine and health sciences/Medical conditions/Infectious diseases/Infectious disease control/Vaccines" ], [ "plos", "/Medicine and health sciences/Pathology and laboratory medicine/Pathogens/Microbial pathogens/Bacterial pathogens/Francisella tularensis" ], [ "plos", "/Research and analysis methods/Immunologic techniques/Immunoassays/Enzyme-linked immunoassays" ] ], "openalex": "W7214702396", "pdf_url": "https://journals.plos.org/plospathogens/article/file?id=10.1371/journal.ppat.1014597&type=printable", "pmcid": null, "pmid": null, "published": "2026-09-29", "publisher": "Public Library of Science", "ris": "https://research.draconitic.com/paper/86j0areg0aqms.ris", "sources": [ { "first_seen": "2026-10-30T12:17:37Z", "native_id": "10.1371/journal.ppat.1014597", "source": "plos", "url": "https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1014597" } ], "subjects": [ { "field": "biology", "origin": "plos:cell biology", "subfield": "cell-biology" }, { "field": "biology", "origin": "plos:immunology", "subfield": "immunology" } ], "title": "Immunopeptidomics reveals conserved and abundant Francisella tularensis proteins as immunogenic CD4 T cell antigens in mice", "title_text": "Immunopeptidomics reveals conserved and abundant Francisella tularensis proteins as immunogenic CD4 T cell antigens in mice", "type": "peer-reviewed", "updated_at": "2026-10-30T12:17:37Z", "url": "https://research.draconitic.com/paper/86j0areg0aqms", "venue": "PLOS Pathogens", "versions": [] }