A) Schematic of BA regulation via enterohepatic recirculation. B) Flare25 mice were fed control (ctrl) diet or 2% cholestyramine (2% chol) diet for two wks; IL-25+ tuft cell frequency in biliary epithelial prep was determined by flow cytometry. Representative of three experiments. C) Flare25 mice fed 2% cholestyramine diet for ten days were injected IP every other day with GW4064 (GW4064 + chol) or vehicle (veh + chol) starting on day 1 of diet. Representative of three experiments. D) Flare25 mice were fed 0.5% cholic acid (CA) diet for the indicated time periods; IL-25+ tuft cell frequency in biliary epithelial prep was determined by flow cytometry. E) Wholemount confocal imaging of Flare25 GB from mice fed chow or 0.5% CA diet for three days. F) Germfree (GF) were fed irradiated 0.5% CA diet in sterile isolators. Frequency of DCLK1+ tuft cells among epithelial cells in total GB/EHBD digest was examined by flow cytometry at indicated timepoints and compared to SPF mice fed irradiated 0.5% CA diet. G) Flare25 mice received 0.2% sodium deoxycholate in drinking water ad libitum. Tuft cell frequency among epithelial cells from total GB/EHBD digest was determined by flow cytometry. H,I) Frequency of DCLK1+ tuft cells among epithelial cells from total GB/EHBD digests was analyzed by flow cytometry in age- and sex-matched H) SPF mice from the UCSF vivarium compared to GF mice and I) Fxr −/− and WT controls. J) The frequency of IL-25+ tuft cells among biliary epithelial cells from total GB/EHBD digests was examined by flow cytometry in Flare25 reporter Cyp8b1−/−, Cyp8b1+/−, and Cyp8b1+/+ mice. K-M) Flare25 mice were subjected to bile duct ligation (BDL) or sham surgery. Seven days later total GB/EHBD digests were analyzed by flow cytometry for frequency of IL-25+ tuft cells among epithelial cells (K,L) and frequency of CD45+ immune cells (M). N-P) Total GB/EHBD digests from Pou2f3−/− and littermate controls were analyzed by flow cytometry seven days after BDL or sham surgery. Total immune cells (CD45+, N), macrophages (CD64+CD11b+Ly6G-, O), and neutrophils (Ly6G+CD11b+CD64-, P) were enumerated. Significance determined by unpaired two-tailed T test (H,I,M) or one-way ANOVA (N-P), *p<.05, **p<.01, ***p<.001, ****p<.0001.