TL1A (TNFSF15) is a member of the tumor necrosis factor (TNF) superfamily, a group of proteins involved in various immune and inflammatory responses. TL1A is primarily expressed on antigen-presenting cells, endothelial cells, and certain epithelial cells. It functions as a ligand, binding to its receptors DR3 and HVEM, thereby modulating immune cell activation, proliferation, and survival. TL1A plays a crucial role in promoting Th1 and Th17 cell differentiation, which are key players in immune defense mechanisms. Additionally, it has been implicated in the pathogenesis of several inflammatory and autoimmune diseases, such as inflammatory bowel disease and psoriasis, where it contributes to chronic inflammation and tissue damage. Ongoing research is exploring the potential of targeting TL1A for therapeutic intervention in these conditions.