TL1A as a Potential Local Inducer of IL17A Expression in Colon Mucosa of Inflammatory Bowel Disease Patients.

Interaction between TL1A and death receptor 3 (DR3) co-stimulates T cells, induces production of several pro-inflammatory cytokines and has been linked to pathogenesis of inflammatory bowel disease (IBD). This study aimed to establish a link between expression of TL1A and selected TL1A-induced pro-inflammatory cytokines involved in IBD pathogenesis (IL-4, IL-13, IL-17A and IFN-γ) and to investigate a connection between serum concentration of TL1A in patients with IBD and activation of peripheral blood T cells. Elevated levels of IL-4 (2.91-fold) and IL-13 (4.05-fold) mRNA were detected in the inflamed colon mucosa of patients with ulcerative colitis (UC), IFN-γ mRNA was upregulated (3.23-fold) in the inflamed colon mucosa of patients with Crohn's disease (CD), whereas upregulation of IL-17A and TL1A mRNA was present in the inflamed colon mucosa of patients with both CD and UC (IL-17A: 4.48-fold and 2.74-fold, TL1A: 3.19-fold and 3.22-fold, respectively) vs. control subjects. We did not detect any changes in DR3 mRNA expression in the investigated groups of patients. TL1A mRNA level in colon mucosa of patients with IBD correlated only with the level of IL-17A mRNA but no other investigated cytokines. In colon mucosa, expression of TL1A and DR3 was localized to enterocytes and lamina propria mononuclear cells. We did not find any correlation between serum concentrations of TL1A and IL-17A or changes of CD4(+) or CD8(+) lymphocytes phenotype in patients with IBD. Therefore, our data indicate that TL1A may contribute to pathogenesis of IBD via local but not systemic induction of IL-17A but not IL-4, IL-13 or IFN-γ.

Sustained TL1A expression modulates effector and regulatory T-cell responses and drives intestinal goblet cell hyperplasia.

The tumor necrosis factor (TNF) superfamily protein TNF-like 1A (TL1A) is the ligand for death receptor 3 (DR3). TL1A is induced on activated dendritic cells (DCs) and its expression has been linked to human inflammatory bowel disease. To address how TL1A might influence intestinal inflammation, we generated transgenic mice that constitutively express TL1A on DCs. TL1A transgenic mice developed striking goblet cell hyperplasia in the ileum that was associated with elevated interleukin (IL)-13 levels in the small intestine. IL-13- and IL-17-producing small intestinal lamina propria T cells were increased in TL1A transgenic mice. TL1A also enhanced regulatory T (Treg) cell turnover in vivo and directly stimulated Treg cell proliferation in vitro. The presence of TL1A attenuated the ability of Treg cells to suppress conventional T cells, an effect that required DR3 signaling in either conventional T cells or Treg cells. Our findings identify mechanisms by which chronic DR3 signaling could promote pathogenesis in inflammatory bowel disease.