Intraepithelial Lymphocytes Suppress Intestinal Tumor Growth by Cell-to-Cell Contact via CD103/E-Cadherin Signal.

BACKGROUND & AIMS: The reason why small intestinal cancer is rarer than colorectal cancer is not clear. We hypothesized that intraepithelial lymphocytes (IELs), which are enriched in the small intestine, are the closest immune cells to epithelial cells, exclude tumor cells via cell-to-cell contact. METHODS: We developed DPE-green fluorescent protein (DPE-GFP) × adenomatous polyposis coli; multiple intestinal neoplasia (APCmin ) mice, which is a T-cell-reporter mouse with spontaneous intestinal tumors. We visualized the dynamics of IELs in the intestinal tumor microenvironment and the interaction between IELs and epithelial cells, and the roles of cell-to-cell contact in anti-intestinal tumor immunity using a novel in vivo live-imaging system and a novel in vitro co-culture system. RESULTS: In the small intestinal tumor microenvironment, T-cell movement was restricted around blood vessels and the frequency of interaction between IELs and epithelial cells was reduced. Genetic deletion of CD103 decreased the frequency of interaction between IELs and epithelial cells, and increased the number of small intestinal tumors. In the co-culture system, wild-type IELs expanded and infiltrated to intestinal tumor organoids from APCmin mice and reduced the viability of them, which was cell-to-cell contact and CD103 dependent. CONCLUSIONS: The abundance of IELs in the small intestine may contribute to a low number of tumors, although this system may not work in the colon because of the sparseness of IELs. Strategies to increase the number of IELs in the colon or enhance cell-to-cell contact between IELs and epithelial cells may be effective for the prevention of intestinal tumors in patients with a high cancer risk.

High-fat diet-derived free fatty acids impair the intestinal immune system and increase sensitivity to intestinal epithelial damage.

In Japan and other Asian countries, increased fat uptake induced by a westernized diet is thought to be associated with an increased incidence of inflammatory bowel disease, colorectal cancer and food allergies; however, the mechanism for this remains unclear. High-fat diet (HFD)-fed mice are common animal models used to examine the effect of fat intake in vivo. HFDs are reported to exacerbate DSS-induced colitis and intestinal tumorigenesis, but the effect of HFDs on the intestines before disease induction is often overlooked. We found that the intestinal and gut-associated lymphoid tissue (GALT) morphology of HFD-fed mice differed from that of standard diet (SD)-fed mice. To clarify the mechanism by which fat intake increases intestinal diseases, we analyzed the morphological and immunological aspects of the intestines of HFD-fed mice as well as the molecular mechanisms and physiology. Feeding an HFD for 3 weeks induced atrophy of the small intestine, colon and GALT and reduced the number of small intestinal intraepithelial lymphocytes (IELs) and lamina propria lymphocytes (LPLs). Feeding an HFD for only one day reduced the number of small intestinal (SI)-IELs and SI-LPLs. The effect of feeding a 3-week HFD continued for 2 weeks after returning to the SD. The effect of the HFD on the intestinal immune system was independent of the gut microbes. We hypothesized that the cytotoxicity of the abundant HFD-derived free fatty acids in the intestinal lumen impairs the intestinal immune system. Both saturated and unsaturated free fatty acids were toxic to intestinal T-cells in vitro. Orally administering free fatty acids reduced the number of SI-IELs and LPLs. Using a lipase inhibitor to reduce the luminal free fatty acids attenuated the HFD-induced changes in the intestinal immune system, while using a statin to reduce the serum free fatty acids did not. Thus, HFD-induced free fatty acids damaged the intestines; this effect was termed "intestinal lipotoxicity". Because sustained reduction of SI-LPLs after HFD feeding exacerbated indomethacin-induced small intestinal damage, lipotoxicity to the human intestines incurred by consuming a westernized diet in Japan may increase intestinal diseases such as IBD, colorectal cancer or food allergies.

CD8αα+ T cells show amoeboid shape and frequent morphological change in vitro, and localize to small intestinal intraepithelial region in vivo.

Intraepithelial lymphocytes (IELs) are very unique in the intestinal immune system. They include γδT cells and CD4-CD8-TCRαß+T cells (double negative: DNT), both of which are specific for the intestine, in addition to CD4+ and CD8+ T cells. IELs exist within the monolayer of the intestinal epithelial cells and dynamically move between lamina propria (LP) and intraepithelial (IE) region. The localization and movement patterns of IEL subsets and the regulatory factors have been unknown. Here, we developed a novel in vitro live imaging system and quantified the motility and morphological changes among subsets of IELs. We identified CD8αα as the key regulatory factor. IELs, especially γδ and DNT cells, showed amoeboid shape and frequent morphological change, while most T cells in MLN or SP showed round shape in vitro. TCR signal, IL-15, gut microbes, CCL25, and integrin αEß7 expression were non-essential for IEL movement in vitro. CD8αα+ cells showed higher motility and larger morphological changes than CD8αα- cells. Adoptive transferred CD8αα+CD4-IELs localized to IE region of recipient NSG mice, while CD8αα-CD4-IELs localized to the LP. Our results showed that the CD8αα/TL signal is essential for the localization of IELs to IE region in vivo. CD8αα/TL may be an effective target to increase the number of IELs, which protects against intestinal infection, allergy, tumorigenesis or inflammation.