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

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 beta(1) integrins expressed by IETs. Therefore, we proposed that IET survival depended on beta(1) integrin binding to collagen IV and showed that beta(1) integrin-collagen IV interactions supported IET survival in vitro. Moreover, the absence of beta(1) integrin expression by T lymphocytes decreased TCR alpha beta(+) 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 beta(1) 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 beta(1) integrins on IETs that were important for their maintenance and for their protective function in mucosal immunity.

Automated summary

This study demonstrates that HVEM and its ligands in intestinal epithelial cells can promote the survival of small intestine IETs in steady state. HVEM enhances the synthesis of basement membrane proteins by epithelial cells, supporting the survival of IETs. Lack of β(1) integrins results in decreased number and movement of IETs.