TL1A (TNF-like ligand 1A, TNFSF15), a cytokine belonging to the tumor necrosis factor (TNF) superfamily. TL1A is expressed on antigen-presenting cells and endothelial cells, particularly in inflamed intestinal tissue. It binds to its receptor DR3 (Death Receptor 3) on immune cells such as T cells and innate lymphoid cells (ILCs). This interaction enhances the production of pro-inflammatory cytokines (e.g., IFN-γ, IL-13, IL-17), promotes the differentiation and survival of pathogenic T-cell subsets (including Th1, Th17, and regulatory T cells), and directly contributes to intestinal inflammation and fibrosis—a hallmark of progressive IBD.