Abstract

TL1A is a TNF-like cytokine that binds to the death-domain receptor (DR)3 and provides costimulatory signals to activated lymphocytes. Through this interaction, TL1A induces secretion of IFN-gamma and may, therefore, participate in the development of T helper-1-type effector responses. In this study, we investigated whether interactions between TL1A and DR3 are involved in the pathogenesis of chronic murine ileitis. We demonstrate that alternative splicing of DR3 mRNA takes place during the activation of lymphocytes, which results in up-regulation of the complete/transmembrane (tm) form of DR3. Using two immunogenetically distinct animal models of Crohn's disease, we demonstrate that induction of intestinal inflammation is associated with significant up-regulation of TL1A and tm DR3 in the inflamed mucosa. In addition, within isolated lamina propria mononuclear cells from mice with inflammation, TL1A is primarily expressed on CD11c(high) dendritic cells. We also report that TL1A acts preferentially on memory CD4(+)/CD45RB(lo) murine lymphocytes by significantly inducing their proliferation, whereas it does not affect the proliferation of the naïve CD4(+)/CD45RB(hi) T helper cell subpopulation. Finally, we demonstrate that TL1A synergizes with both the cytokine-dependent IL-12/IL-18 pathway and with low-dose stimulation of the T cell receptor to significantly induce the secretion of IFN-gamma via an IL-18-independent pathway. Our results raise the possibility that interaction(s) between TL1A expressed on antigen-presenting cells and tm DR3 on lymphocytes may be of particular importance for the pathogenesis of chronic inflammatory conditions that depend on IFN-gamma secretion, including inflammatory bowel disease. Blockade of the TL1A/DR3 pathway may, therefore, offer therapeutic opportunities in Crohn's disease.