Glucocorticoid-induced tumor necrosis factor receptor-related (GITR)-Fc fusion protein inhibits GITR triggering and protects from the inflammatory response after spinal cord injury

Glucocorticoid-induced tumor necrosis factor receptor-related (GITR) protein is a costimulatory molecule that plays a role in inflammation so that GITR-Fc fusion protein can exert an antiinflammatory effect. To investigate the mechanism by which GITR-Fc exerts its effects, we first used GITR knock-out (GITR^-/-) mice to verify whether GITR ligand (GITRL)/GITR system played a pro-inflammatory role in the spinal cord injury (SCI) model. It is noteworthy that less pronounced disease was induced in GITR^-/- compared with GITR^+/+ mice. We then evaluated the effect of GITR-Fc fusion protein against SCI-induced injuries in GITR^-/- and wild-type (GITR^+/+) mice. Administration of GITR-Fc ameliorated SCI-induced inflammation in GITR^+/+ mice as evaluated through: 1) histological damage and apoptosis, 2) modulation of apoptosis-related transduction factors (Bax and Bcl-2), 3) expression of inflammatory markers [nitrotyrosine, inducible nitric-oxide synthase, interleukin (IL)-2, IL-12, and tumor necrosis factor-α], and 4) T-lymphocyte infiltration. GITR-Fc was effective in GITR^+/+ but not in GITR^-/-, suggesting that in this experimental model, its anti-inflammatory action was due to inhibition of GITR triggering and not to GITRL activation. In conclusion, GITR plays a role in SCI, and administration of GITR-Fc results in amelioration of SCI severity, prompting further studies on the potential anti-inflammatory properties of GITR-Fc.