LIGHT is constitutively expressed on T and NK cells in the human gut and can be induced by CD2-mediated signaling.

The TNF superfamily cytokine, lymphotoxin-like inducible protein that competes with glycoprotein D for binding herpesvirus entry mediator on T cells (LIGHT; TNFSF14), can augment T cell responses inducing IFN-gamma production and can drive pathological gut inflammation when expressed as a transgene in mouse T cells. LIGHT expression by human intestinal T cells suggests the possibility that LIGHT may play a key role in regulation of the mucosal immune system. A nonenzymatic method was developed for the isolation of T cells from the human lamina propria, permitting analysis of native cell surface protein expression. Cell surface LIGHT was constitutively expressed on mucosal T and NK cells and a subpopulation of gut-homing CD4(+) T cells in the periphery. In addition, CD2-mediated stimulation induced efficient LIGHT expression on intestinal CD4(+) T cells, but not on peripheral blood T cells, suggesting a gut-specific, Ag-independent mechanism for LIGHT induction. By contrast, herpesvirus entry mediator expression on gut T cells was unperturbed, implicating the transcriptional regulation of LIGHT as a mechanism modulating signaling activity in the gut. Quantitative analysis of LIGHT mRNA in a cohort of inflammatory bowel disease patients indicated elevated expression in biopsies from small bowel and from inflamed sites, implicating LIGHT as a mediator of mucosal inflammation.