We used immunopeptidomics to identify MHC class II peptides and antigens of the intracellular bacterial pathogen Francisella tularensis. We infected dendritic cells from mouse bone marrow with F. tularensis LVS strain or its dsbA gene mutant strain, isolated peptide-MHC-II complexes, and identified the peptides by LC-MS/MS. The identified bacterial peptides were subsequently validated as CD4 T cell epitopes in a mouse model of tularemia. We further performed proteomic analysis of LVS and LVSΔdsbA strains to determine whether there is any possible relationship between the discovered MHC-II antigens and the proteome.