Figure 6. Succinate is produced by Tritrichomonas and sufficient to activate the tuft cell – ILC2 circuit.

(A and B) GF mice monocolonized with Tritrichomonas and concentrations of acetate (A) and succinate (B) measured in the cecal content after 6 weeks. (C) Metabolite receptor mRNA expression quantified by qPCR in tuft cells versus other epithelial cells sorted from small intestine (SI) and normalized to levels in non-tuft epithelial cells. (D–F) Tritrichomonas-free IL-13-reporter (Sm13) mice were treated with succinate, acetate or a SCFA mix (acetate, butyrate, propionate) in drinking water for 4 days. Expression of Ki-67 and IL-13 by ILC2s in SI quantified by flow cytometry and representative dot plot from wild-type (WT) mice shown (D). Expression of Ki-67 (E) and IL-13 (F) by ILC2s from WT, Pou2f3^−/−, Il25^−/− and Trpm5^−/− mice treated with indicated solutions. (G) Tritrichomonas-free WT mice treated with 100 mM succinate in drinking water for 10 days. Frequencies of tuft cells in SI by flow cytometry. (H and I) Tritrichomonas-free A20^flR+ and Il25^−/−A20^flR+ mice treated with 100 mM succinate in drinking water for 25 days and frequencies of tuft cells (H) and SI length (I) analyzed. Data from one experiment (A, B) or from one experiment representative of at least two independent experiments (C, D, G–I) or pooled from multiple independent experiments (E, F). C, mean and s.e.m.; n = 3. **p < 0.01, ****p < 0.0001; ns, not significant by Mann-Whitney U or one-way ANOVA.