Lactobacillus reuteri induces gut intraepithelial CD4 + CD8αα + T cells

Tolerogenic T cells need probiotics CD4 + CD8αα + double-positive intraepithelial lymphocytes (DP IELs) are a recently discovered class of intestinal T cells believed to take part in a variety of immune responses, including oral tolerance. These cells are absent in germ-free mice, but the mechanisms driving their development are unclear. Cervantes-Barragan et al. found that a particular species of probiotic bacteria, Lactobacillus reuteri , induces DP IELs. This does not occur by stimulating the immune system directly. Instead, L. reuteri generates a specific derivative of dietary tryptophan that promotes differentiation of DP IEL precursors. These findings underscore the delicate interplay between benign bacteria, diet, and gut health. Science , this issue p. 806