TIR-Domain-Containing Adapter-Inducing Interferon-β (TRIF) Regulates CXCR5+ T helper Cells in the Intestine

Establishing an effective humoral immunity is an important host defense mechanism in intestinal mucosa. T follicular helper (Tfh) cells are a spectrum of CXCR5 expressing T helper cells that induce antigen-specific B cell differentiation. Because the differentiation of T helper cells is largely regulated by innate immunity, we addressed whether TRIF signaling regulates Tfh cell differentiation and its ability to trigger humoral immune responses in the intestine.

CD4⁺CXCR5⁺ T cells, B cells, and plasma cells in the Peyer's patches (PPs) of WT and TRIF-deficient (Trif^LPS2) mice were analyzed by flow cytometry at the baseline, 9 days post primary infection, and 7 days post-secondary infection with Y. enterocolitica. Y. enterocolitica-specific CD4⁺CXCR5⁺ T cells were generated in vitro by co-culturing peritoneal macrophages with splenic naïve T cells in the presence of Y. enterocolitica lysate. WT and Trif^LPS2 mice received CD4⁺CXCR5⁺ T cells isolated either from Y. enterocolitica-primed WT mice or generated in vitro. These mice were infected with Y. enterocolitica and followed up to 4 weeks. Y. enterocolitica-specific IgA and IgG were measured in stool and serum samples, respectively.

At baseline, CD4⁺CXCR5⁺ T cell proportion was higher but the proportion of B cells and plasma cells was lower in the PPs of Trif^LPS2 mice compared to WT mice. After infection, the proportion of plasma cells also became higher in the PPs of Trif^LPS2 mice compared to WT mice. Corresponding increase of Y. enterocolitica-specific stool IgA but not serum IgG was found in Trif^LPS2 mice compared to WT mice. Both in vivo isolated and in vitro generated CD4⁺CXCR5⁺ T cells induced protective immunity against Y. enterocolitica infection.

Our results reveal a novel role of TRIF in the regulation of humoral immunity in the intestine that can be utilized as a basis for a unique vaccine strategy.