For ex vivo culture of small intestinal tissues of mouse, ileum was isolated and cultured as described previously72 with slight modifications. Briefly, distal ileum segments (1 cm in length) with or without Peyer’s patches were collected, gently opened with a sterilized operating scissors, washed five times with PBS supplemented with 10% penicillin/streptomycin, and transferred to 12-well plates for further incubation in complete DMEM.