Francisella tularensis induces Th1 like MAIT cells conferring protection against infection.

F. tularensis LVS activates MAIT reporter cells in vitro in an MR1-dependent manner and induces a systemic MAIT cell response in vivo
To confirm that F. tularensis LVS, a riboflavin biosynthesis proficient bacteria as shown in the database Kyoto Encyclopedia of Genes and Genomes, can stimulate MAIT cells, we used an in vitro activation assay with Jurkat.MAIT.AF7 reporter cells co-cultured with Class I reduced (C1R) Ag-presenting cells expressing MR1 (C1R.MR1 cells) as antigen presenting cells, as previously described10. Both F. tularensis culture supernatant and lysate were able to stimulate Jurkat.MAIT cells in this assay as assessed by the upregulation of cell surface CD69 expression (Fig. 1A). In addition, C1R.MR1 cells infected for 4h with a multiplicity of infection (MOI) of 100 could stimulate activation of Jurkat.MAIT cells (Fig. 1A). Anti-MR1 monoclonal antibody (mAb) (26.5), but not an isotype control mAb, completely blocked this response, consistent with MR1-dependent activation. Similar to previous studies using other bacteria25,40, these data demonstrated that F. tularensis LVS is capable of producing Ags that stimulate MAIT cells in an MR1-dependent manner.

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