Gut Microbial-specific CD4+T cells from Crohn’s Disease Patients exhibit a Proinflammatory Th17 Phenotype

Experimental models have led to the theory that intestinal inflammation, as seen in Crohn's disease (CD), results from a loss of tolerance towards commensal microorganisms. In fact, about half of CD patients develop antibodies towards gut microbial antigens. There is however little evidence supporting the existence of a microbial-specific T cell response in CD. In testing reactivity to several gut microbial antigens in peripheral blood mononuclear cells, we detected T cell reactivity towards some antigens including FlaX, Fla2, and YidX in healthy individuals and CD patients; T cell proliferation was however higher among CD patients. Intracellular cytokine staining revealed the presence of Th17, Th1 and Th17/Th1 cells among the FlaX, Fla2 and YidX-specific T cells. While the percentage of Th1 cells was similar, Th17 and Th1/Th17 frequency was higher in CD patients compared to healthy individuals. Microarray and real time-PCR gene analysis of sorted gut microbial-specific T cells showed a Th7-biased transcriptional profile in CD patients’ microbial-specific T cells. Supernatants from CD activated FlaX, Fla2 and YidX-specific T cells induced higher expression of CXCL1 CXCL8, and CCL20 in healthy colonic crypts, which diminished upon IL-17 neutralization, demonstrating the proinflammatory potential of these cells in the intestinal mucosa. Collectively, our data indicate that T cells that react to gut microbial antigens have been differently imprinted towards a Th17 phenotype in CD. We hypothesize that these cells represent a circulating microbial-specific memory T cell pool that may contribute to sustain gut inflammation in CD; their identification opens new avenues for antigen-directed therapies.