Glucocorticoid-induced TNFR family-related protein (GITR) activation exacerbates murine asthma and collagen-induced arthritis

Glucocorticoid-induced TNFR family-related protein (GITR) is expressed at low levels on resting T cells, B cells and macrophages but at high levels on regulatory T cells (Treg). Although GITR expression is up-regulated on CD4⁺ effector cells upon activation, the role of GITR in Th1 and Th2 cell development is unclear. We report here that activation of GITR signalling by anti-GITR antibody markedly enhanced the induction of both Th1 and Th2 cytokine production by naive CD4⁺CD25^- T cells. Consistent with this observation, anti-GITR antibody significantly enhanced the expression of the key Th1 (T-bet) and Th2 (GATA3) transcription factors in vitro. Administration of anti-GITR mAb in a murine model of arthritis significantly exacerbated the severity and onset of joint inflammation with elevated production of TNF-α, IFN-γ, IL-5, and collagen-specific IgG1. Administration of anti-GITR mAb also significantly exacerbated murine allergic airways inflammation with elevated production of OVA-specific IFN-γ, IL-2, IL-4, IL-5, and IgE. Finally, we demonstrated that adoptive transfer of CD4⁺GITR⁺ T cells effectively abolished airway inflammation induced in SCID mice reconstituted with CD4⁺GITR T cells. Our results therefore provide direct evidence that GITR can modulate both Th1- and Th2-mediated inflammatory diseases, and may be a potential target for therapeutic intervention.