Francisella tularensis lipoproteins are T-independent antigens that activate TLR2 on B cells and elicit protective antibodies 4249

Description Francisella tularensis is a gram-negative bacterium that causes tularemia. We previously showed that F. tularensis proteins Tul4 and FTT1103 are triacylated lipoproteins that potently stimulate TLR2/TLR1. Here we tested whether Tul4 or FTT1103 could act as self-adjuvanted vaccine antigens. Confirming this, immunization of mice with purified Tul4 or FTT1103 elicited high titers of antigen-specific IgM, IgG1, IgG2b, IgG2c and IgG3. This response was not observed with the deacylated lipoproteins and was completely dependent on TLR2. Tcra-/- mice immunized with Tul4 showed antigen-specific IgM titer similar to WT mice but decreased IgG3 and undetectable IgG1, IgG2b and IgG2c, suggesting these lipoproteins can also act as T-independent antigens. Adoptive transfer experiments and bone marrow chimeras showed that B1 B cell-intrinsic TLR2 expression was required for production of Tul4-specific IgM while TLR2 expression on bone marrow-derived B2 B cells were responsible for production of IgG3 and IgG2b. Splenic B cells stimulated in vitro with Tul4 secreted pro-inflammatory cytokines (IL-6, TNFα) and increased expression of activation surface markers (CD69, CD80/86). Finally, Tul4 vaccination reduced bacterial burden and protected mice from F. tularensis LVS strain lung infection. Our study is the first to show that TLR2 stimulation of B cells is sufficient for IgM production in absence of T cell help and that Tul4 can be an attractive antigen for vaccination in absence of adjuvant. Funding Sources NIH R01 AI175174-01 NIH R01 AI158064-01 Topic Categories Microbial, Parasitic, and Fungal Immunology (MPF)