Chun-Pyo Hong^1,2,3, Areum Park², Bo-Gie Yang¹, Chang Ho Yun¹, Min-Jung Kwak^4,5, Gil-Woo Lee^1,2, Jung-Hwan Kim^1,2, Min Seong Jang^1,2, Eun-Jung Lee^1,2, Eun-Ji Jeun^1,2, Gihoon You², Kwang Soon Kim¹, Youngwoo Choi⁶, Ji-Hwan Park⁷, Daehee Hwang^7,8, Sin-Hyeog Im^1,2, Jihyun F. Kim⁴, Yoon-Keun Kim⁹, Ju-Young Seoh³, Charles D. Surh^1,2, You-Me Kim^{2, 6,*}, Myoung Ho Jang<sup>1,10,*

1</sup> Academy of Immunology and Microbiology, Institute for Basic Science, Pohang 37673, Republic of Korea
² Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang 37673, Republic of Korea
³ Department of Microbiology, Graduate School of Medicine, Ewha Womans University, Seoul 07985, Republic of Korea
⁴ Department of Systems Biology and Division of Life Sciences, Yonsei University, Seoul 03922, Republic of Korea
⁵ Biosystems and Bioengineering Program, Korea University of Science and Technology, Daejeon 34113, Republic of Korea
⁶ Department of Life Science, Pohang University of Science and Technology, Pohang 37673, Republic of Korea
⁷ Department of Chemical Engineering, Pohang University of Science and Technology, Pohang 37673, Republic of Korea
⁸ Center for Plant Aging Research, Institute for Basic Science, Daegu 42988, Republic of Korea
⁹ Research Institute, MD Healthcare, Seoul 03923, Republic of Korea
¹⁰ WPI Immunology Frontier Research Center, Osaka University, Suita 565-0871, Japan

^*Corresponding authors

Authorship note: Chun-Pyo Hong, Areum Park and Bo-Gie Yang contributed equally to this work.

Background & Aims
Obesity and metabolic syndrome have been associated with alterations to the intestinal microbiota. However, few studies examined the effects of obesity on the intestinal immune system. We investigated changes in subsets of intestinal CD4+ T-helper (Th) cells with obesity and the effects of gut-tropic Th17 cells in mice on a high-fat diet (HFD).

Methods
We isolated immune cells from small intestine and adipose tissue of C57BL/6 mice fed a normal chow diet or a HFD for 10 weeks and analyzed the cells by flow cytometry. Mice fed a vitamin A-deficient HFD were compared with mice fed a vitamin A-sufficient HFD. Obese RAG1-deficient mice were given injections of only T regulatory cells or a combination of T regulatory cells and Th17 cells (wild type or deficient in integrin β7 subunit-deficient or interleukin 17 [IL17]). Mice were examined for weight gain, fat mass, fatty liver, glucose tolerance, and insulin resistance. Fecal samples were collected before and after T-cell transfer and analyzed for microbiota composition by metagenomic DNA sequencing and quantitative PCR.

Results
Mice placed on a HFD became obese, which affected the distribution of small intestinal CD4+ TH cells. Intestinal tissues from obese mice had significant reductions in the proportion of Th17 cells but increased proportion of Th1 cells, compared with intestinal tissues from non-obese mice. Depletion of vitamin A in obese mice further reduced the proportion of Th17 cells in small intestine; this reduction correlated with more weight gain and worsening of glucose intolerance and insulin resistance. Adoptive transfer of in vitro-differentiated gut-tropic Th17 cells to obese mice reduced these metabolic defects, which required the integrin β7 subunit and IL17. Delivery of Th17 cells to intestines of mice led to expansion of commensal microbes associated with leanness.

Conclusions
In mice, intestinal Th17 cells contribute to development of a microbiota that maintains metabolic homeostasis, via IL17. Gut-homing Th17 cells might be used to reduce metabolic disorders in obese individuals.

Key words : glucose tolerance; mucosal immunity; intestinal microbiota