Epithelial HVEM maintains intraepithelial T cell survival and contributes to host protection

Intestinal epithelia maintain T cells
Immune surveillance of the intestinal epithelium is crucial for intestinal homeostasis and protecting against infection. However, how the intestinal epithelium helps induce immune surveilling intraepithelial T cells (IET) is unclear. Here, Seo, Takahashi, and Wang et al. used mouse knockout models to demonstrate that herpes virus entry mediator (HVEM), a TNFR superfamily member, expression on intestinal epithelial cells was crucial for the survival and patrolling ability of intraepithelial CD8α T cells. LIGHT, a ligand for HVEM, was crucial for the HVEM-driven effects seen. Epithelial knockout of HVEM led to poorer protection against intestinal S. typimurium infection. Together, these data show that HVEM expression in intestinal epithelial cells is involved in IET-mediated immune surveillance of the small intestine

Intraepithelial T cells (IETs) are in close contact with intestinal epithelial cells and the underlying basement membrane, and they detect invasive pathogens. How intestinal epithelial cells and basement membrane influence IET survival and function, at steady state or after infection, is unclear. The herpes virus entry mediator (HVEM), a member of the TNF receptor superfamily, is constitutively expressed by intestinal epithelial cells and is important for protection from pathogenic bacteria. Here, we showed that at steady-state LIGHT, an HVEM ligand, binding to epithelial HVEM promoted the survival of small intestine IETs. RNA-seq and addition of HVEM ligands to epithelial organoids indicated that HVEM increased epithelial synthesis of basement membrane proteins, including collagen IV, which bound to β1 integrins expressed by IETs. Therefore, we proposed that IET survival depended on β1 integrin binding to collagen IV and showed that β1 integrin–collagen IV interactions supported IET survival in vitro. Moreover, the absence of β1 integrin expression by T lymphocytes decreased TCR αβ+ IETs in vivo. Intravital microscopy showed that the patrolling movement of IETs was reduced without epithelial HVEM. As likely consequences of decreased number and movement, protective responses to Salmonella enterica were reduced in mice lacking either epithelial HVEM, HVEM ligands, or β1 integrins. Therefore, IETs, at steady state and after infection, depended on HVEM expressed by epithelial cells for the synthesis of collagen IV by epithelial cells. Collagen IV engaged β1 integrins on IETs that were important for their maintenance and for their protective function in mucosal immunity