Diet-mediated constitutive induction of novel IL4+ ILC2 cells maintains intestinal homeostasis in mice

Group 2 innate lymphoid cells (ILC2s) expressing IL-5 and IL-13 are localized at various mucosal tissues and play critical roles in the induction of type 2 inflammation, response to helminth infection, and tissue repair. Here we reveal a unique ILC2 subset in the mouse intestine that constitutively expresses IL-4 together with GATA3, ST2, KLRG1, IL-17RB, and IL-5. In this subset, IL-4 expression is regulated by mechanisms similar to but distinct from those observed in T cells and is partly affected by IL-25 signaling. Although the absence of the microbiota had marginal effects, feeding mice with a vitamin B1-deficient diet compromised the number of intestinal IL-4+ ILC2s. The decrease in the number of IL-4+ ILC2s caused by the vitamin B1 deficiency was accompanied by a reduction in IL-25-producing tuft cells. Our findings reveal that dietary vitamin B1 plays a critical role in maintaining interaction between tuft cells and IL-4+ ILC2s, a previously uncharacterized immune cell population that may contribute to maintaining intestinal homeostasis.

Methods
ILC2 cells were isolated from colon and lung of GF mice and SPF mice. Colonic epithelial cells were isolated from mice fed with control diet or vitamin B1-free diet. Total RNA was extracted using TRIzol (Invitrogen) and an RNA library was prepared using a NEBNext Ultra RNA Library Prep Kit for Illumina (New England Biolabs) according to the manufacturer’s instructions. After assessing the library quality, sequencing was conducted on a HiSeq 1500 system (Illumina) using single-ended 50-bp reads. The sequenced reads were mapped to the mouse reference genome (mm9, NCBI build 37) and normalized to fragments per kilobase per million reads (FPKM) values using the Tophat and Cufflinks software pipeline.