Interleukin-2 (IL-2) withdrawal is a physiologic process inducing cell death in activated T lymphocytes. Glucocorticoidinduced leucine zipper (GILZ) has recently been identified as a protein modulating T-cell receptor activation by repressing various signaling pathways. We report here that IL-2 deprivation leads to expression of GILZ in T lymphocytes. We then characterized the human gilz promoter and showed that FoxO3 (Forkhead box class O3) binding to the Forkhead responsive elements identified in the promoter is necessary for induction of gilz expression upon IL-2 withdrawal. To assess the functional consequences of this induction, we used 2 strategies, GILZ overexpression and GILZ silencing in murine IL-2-dependent CTLL-2 cells. GILZ overexpression protects CTLL-2 cells from IL-2 withdrawal-induced apoptosis, whereas cell death is accelerated in cells unable to express GILZ. Concomitantly, the expression of Bim is inhibited in GILZ-overexpressing cells and enhanced when GILZ expression is impaired. Furthermore, GILZ inhibits FoxO3 transcriptional activity that leads to inhibition of Bim expression but also to down-regulation of GILZ itself. Therefore, GILZ is a transiently expressed protein induced upon IL-2 withdrawal that protects T cells from the onset of apoptosis. ( IntroductionA complex network of cytokines controls the development, maturation, homeostasis, and responses of the immune system. Immune responses typically involve clonal expansion of activated T cells, which must be eliminated at the end of the response to preserve homeostasis. 1 Interleukin-2 (IL-2) is secreted by activated T cells and plays a role in their survival and proliferation. IL-2 is also involved in the regulation of homeostasis of the lymphoid tissue, as IL-2 induces apoptosis of activated T cells in an "active" way involving regulation of Fas and Fas ligand (FasL) expression and in a "passive" way due to deprivation of this survival factor. 2 Binding of IL-2 to its receptor triggers a signaling cascade that induces, among others, the phosphoinositide 3-kinase (PI3K) pathway involved in T-cell proliferation and survival. 3,4 One of the downstream effectors of PI3K signaling is protein kinase B (PKB)/Akt. PKB is a serine/threonine kinase promoting cell survival by targeting proapoptotic proteins. 5 PKB exerts one of its inhibitory effects by phosphorylating members of the Forkhead family of transcription factors (Forkhead box class O1 [FoxO1], FoxO3, and FoxO4), which contain 3 RXRXXS/T consensus phosphorylation sites for PKB. 6 Interruption of the PI3K/PKB pathway following IL-2 deprivation results in dephosphorylation of FoxO proteins leading to their translocation to the nucleus and transcription of target genes.Brunet et al 7 were the first to ascribe a role to FoxO proteins in programmed cell death, reporting that overexpression of a constitutive active form of FoxO3 induces apoptosis of Jurkat T cells in a Fas-dependent manner. Fas-independent mechanisms of apoptosis induced by FoxO proteins have also been observed in othe...

Particles possess huge specific surface area and therefore nanomaterials exhibit unique characteristics, such as special physical properties and chemical hyper-reactivity, which make them particularly attractive but also raise numerous questions concerning their safety. Interactions of nanomaterials with the immune system can potentially lead to immunosuppression, hypersensitivity (allergy), immunogenicity and autoimmunity, involving both innate and adaptive immune responses. Inherent physical and chemical NP characteristics may influence their immunotoxicity, i.e., the adverse effects that can result from exposure. This review will focus on the possible interaction of nanomaterials including protein aggregates with the innate immune system with specific emphasis on antigen-presenting cells, i.e., dendritic cells, macrophages and monocytes.