Selection of cross-reactive T cells by commensal and food-derived yeasts drives cytotoxic T H 1 cell responses in Crohn's disease.

Aberrant CD4 + T cell reactivity against intestinal microorganisms is considered to drive mucosal inflammation in inflammatory bowel diseases. The disease-relevant microbial species and the corresponding microorganism-specific, pathogenic T cell phenotypes remain largely unknown. In the present study, we identified common gut commensal and food-derived yeasts, as direct activators of altered CD4 + T cell reactions in patients with Crohn's disease (CD). Yeast-responsive CD4 + T cells in CD display a cytotoxic T helper cell (T H 1 cell) phenotype and show selective expansion of T cell clones that are highly cross-reactive to several commensal, as well as food-derived, fungal species. This indicates cross-reactive T cell selection by repeated encounter with conserved fungal antigens in the context of chronic intestinal disease. Our results highlighted a role of yeasts as drivers of aberrant CD4 + T cell reactivity in patients with CD and suggest that both gut-resident fungal commensals and daily dietary intake of yeasts might contribute to chronic activation of inflammatory CD4 + T cell responses in patients with CD.