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Tumor necrosis factor receptor superfamily member 18 (TNFRSF18), also known as glucocorticoid-induced tumor necrosis factor receptor family-related protein (GITR) TNFRSF18 (also known as activation-inducible TNF receptor (AITR), glucocorticoid-induced tumor necrosis factor receptor family-related protein (GITR), CD357, GITR-D) has increased expression upon T-cell activation, and is thought to play a key role in dominant immunological self-tolerance maintained by CD25(+)CD4(+) regulatory T cells. In inflammatory cells, GITR expression indicates a possible molecular link between steroid use and complicated acute sigmoid diverticulitis; increased MMP-9 expression by GITR signaling might explain morphological changes in the colonic wall in diverticulitis. Its ligand, GITRL, activates GITR which could then influence the activity of effector and regulatory T cells, participating in the development of several autoimmune and inflammatory diseases, including autoimmune thyroid disease and rheumatoid arthritis. In systemic lupus erythematosus (SLE) patients, serum GITRL levels are increased compared with healthy controls. GITR and its ligand, GITRL, are possibly involved in the pathogenesis of primary Sjogren's syndrome (pSS). GITR is inactivated during tumor progression in Multiple Myeloma (MM); restoration of GITR expression in GITR deficient MM cells leads to inhibition of MM proliferation and induction of apoptosis, thus playing a pivotal role in MM pathogenesis and disease progression. Regulatory T-cells (Tregs) in liver tumor up-regulate the expression of GITR compared with Tregs in tumor-free liver tissue and blood. Regulatory single nucleotide polymorphisms (SNPs) in the promoter regions of the TNFRSF18 gene have been identified in a group of male Gabonese individuals exposed to a wide array of parasitic diseases such as malaria, filariasis and schistosomiasis, and may serve as a basis to study parasite susceptibility in association studies.
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