By comparing mRNA species expressed in dexamethasone (DEX)-treated and untreated murine thymocytes, we have identified a gene, glucocorticoid-induced leucine zipper (GILZ), encoding a new member of the leucine zipper family. GILZ was found expressed in normal lymphocytes from thymus, spleen, and lymph nodes, whereas low or no expression was detected in other nonlymphoid tissues, including brain, kidney, and liver. In thymocytes and peripheral T cells, GILZ gene expression is induced by DEX. Furthermore, GILZ expression selectively protects T cells from apoptosis induced by treatment with anti-CD3 monoclonal antibody but not by treatment with other apoptotic stimuli. This antiapoptotic effect correlates with inhibition of Fas and Fas ligand expression. Thus, GILZ is a candidate transcription factor involved in the regulation of apoptosis of T cells.

GITR (glucocorticoid-induced TNFR family related gene) is a member of the TNFR superfamily (TNFRSF) that is expressed in different cell types, including T lymphocytes. Because of a high homology in its cytoplasmic region with other known costimulatory members of the TNFRSF, we investigated whether GITR played a costimulatory role in T lymphocyte subpopulations. Our results show that the proliferation response of CD8 + and CD4 + peripheral T cell subpopulations was potentiated when a GITR costimulus was added to an anti-CD3 stimulus. Furthermore, expression of the main activation-induced receptor (IL-2R § ) and production of IL-2 and IFN-+ were increased more with a GITR costimulus than with anti-CD3 alone. GITR stimulation also enhanced anti-CD3-induced ERK phosphorylation, suggesting that GITR is involved in MAPK-pathway activation. Interestingly, CD4 + CD25 + regulatory T cell (Treg cell) proliferation was triggered by the GITR costimulus; Treg cell proliferation was paralleled by the loss of the anergic phenotype and suppressor activity. Nevertheless, unstimulated GITR -/-CD4 + CD25 + and GITR +/+ CD4 + CD25 + cells were equally able to exert suppressor activity on CD4 + CD25 -responder cells. These results indicate a novel function for GITR as costimulatory molecule of T cell subsets.

No abstract

Glucocorticoids and interleukin 10 (IL-10) prevent macrophage activation. In murine lymphocytes, glucocorticoids induce expression of glucocorticoid-induced leucine zipper (GILZ), which prevents the nuclear factor B (NF-B)-mediated activation of transcription. We investigated whether GILZ could account for the deactivation of macrophages by glucocorticoids and IL-10. We found that GILZ was constitutively produced by macrophages in nonlymphoid tissues of humans and mice. Glucocorticoids and IL-10 stimulated the production of GILZ by macrophages both in vitro and in vivo. Transfection of the macrophagelike cell line THP-1 with the GILZ gene inhibited the expression of CD80 and CD86 and the production of the proinflammatory chemokines regulated on activation normal T-cell expressed and secreted (CCL5) and macrophage inflammatory protein 1␣ (CCL3). It also prevented toll-like receptor 2 production induced by lipopolysaccharide, interferon␥, or an anti-CD40 mAb, as well as NF-B function. In THP-1 cells treated with glucocorticoids or IL-10, GILZ was associated with the p65 subunit of NF-B. Activated macrophages in the granulomas of patients with Crohn disease or tuberculosis do not produce GILZ. In contrast, GILZ production persists in tumorinfiltrating macrophages in Burkitt lymphomas. Therefore, GILZ appears to play a key role in the anti-inflammatory and immunosuppressive effects of glucocorticoids and IL-10. Glucocorticoid treatment stimulates GILZ production, reproducing an effect of IL-10, a natural anti-inflammatory agent. The development of delayedtype hypersensitivity reactions is associated with the down-regulation of GILZ gene expression within lesions. In contrast, the persistence of GILZ gene expression in macrophages infiltrating Burkitt lymphomas may contribute to the failure of the immune system to reject the tumor. IntroductionGlucocorticoids (GCs) are potent anti-inflammatory and immunosuppressive drugs. Their therapeutic effects are largely due to their ability to inhibit many functions of macrophages and of other antigen-presenting cells. Interleukin 10 (IL-10) is an antiinflammatory cytokine that has a number of effects in common with GCs, particularly those affecting macrophage functions. Both GCs 1-13 and IL-10 (reviewed in Stordeur and Goldman 14 ) inhibit antigen processing, the expression of HLA, CD80, and CD86, and the synthesis of nitric oxide, cyclo-oxygenase 2, adhesion molecules, cytokines, and chemokines. The intracellular events induced by the binding of GCs and IL-10 to their respective receptors are not fully understood, but they also share certain characteristics. In particular, both GCs and IL-10 interfere with the function of the transcriptional activators AP-1 and NF-B (reviewed in Stordeur and Goldman, 14 Karin, 15 and Barnes and Karin 16 ). Pathogenassociated molecular patterns (PAMPs) of bacterial components activate macrophages by binding to the toll-like receptors (TLRs), which trigger the nuclear factor B (NF-B) pathway and stimulate the production of inflammatory protein...