Ahjoku Amadi-Obi

TH17 cells contribute to uveitis and scleritis and are expanded by IL-2 and inhibited by IL-27/STAT1.

T-helper type 17 cells (TH17) are implicated in rodent models of immune-mediated diseases. Here we report their involvement in human uveitis and scleritis, and validate our findings in experimental autoimmune uveoretinitis (EAU), a model of uveitis. TH17 cells were present in human peripheral blood mononuclear cells (PBMC), and were expanded by interleukin (IL)-2 and inhibited by interferon (IFN)-γ. Their numbers increased during active uveitis and scleritis and decreased following treatment. IL-17 was elevated in EAU and upregulated tumor necrosis factor (TNF)-α in retinal cells, suggesting a mechanism by which TH17 may contribute to ocular pathology. Furthermore, IL-27 was constitutively expressed in retinal ganglion and photoreceptor cells, was upregulated by IFN-γ and inhibited proliferation of TH17. These findings suggest that TH1 cells may mitigate uveitis by antagonizing the TH17 phenotype through the IFN-γ–mediated induction of IL-27 in target tissue. The finding that IL-2 promotes TH17 expansion provides explanations for the efficacy of IL-2R antibody therapy in uveitis, and suggests that antagonism of TH17 by IFN-γ and/or IL-27 could be used for the treatment of chronic inflammation.

STAT3 Protein Promotes T-cell Survival and Inhibits Interleukin-2 Production through Up-regulation of Class O Forkhead Transcription Factors

Much is known about the role of STAT3 in regulating differentiation of interleukin-17-producing Th17 cells, but its function in other lymphocyte subsets is not well understood. In this report, we reveal wide-ranging functions of STAT3 in T-cells and provide evidence that STAT3 is convergence point for mechanisms that regulate lymphocyte quiescence and those controlling T-cell activation and survival. We show here that STAT3 inhibits T-lymphocyte proliferation by up-regulating the expression of Class-O Forkhead transcription factors, which play essential roles in maintaining T-cells in quiescent state. We further show that STAT3 binds directly to FoxO1 or FoxO3a promoter and that STAT3-deficiency resulted in down-regulation of the expression of FoxO1, FoxO3a and FoxO-target genes (IκB and p27Kip1). Compared with wild-type T-cells, STAT3-deficient T-cells produced more IL-2, due in part, to marked decrease in IκB-mediated sequestration of NF-κB in the cytoplasm and resultant enhancement of NF-κB activation. However, the high level of IL-2 production by STAT3-deficient T-cells was partially restored to normal levels by overexpressing FoxO1. It is notable that their exaggerated increase in IL-2 production rendered STAT3-deficient lymphocytes more susceptible to activation-induced cell death, suggesting that STAT3 might protect T-cells from apoptosis by limiting their production of IL-2 through up-regulation of FoxO1/FoxO3a expression. Moreover, we found that STAT3 enhanced survival of activated T-cells by up-regulating OX-40 and Bcl-2 while down-regulating FasL and Bad expression, suggesting that similar to role of FoxOs in regulating the lifespan of worms, STAT3 and FoxO pathways converge to regulate lifespan of T-lymphocytes.

Retinal cells suppress intraocular inflammation (uveitis) through production of interleukin-27 and interleukin-10

Neuronal or photoreceptor deficit observed in uveitis and multiple sclerosis derives in part from inability to control inflammatory responses in neuroretina or brain. Recently, IL‐27 was found to play a role in suppressing experimental autoimmune uveitis and experimental autoimmune encephalomyelitis, two animal models that share essential pathological features of human uveitis and multiple sclerosis, respectively. However, the mechanism by which interleukin‐27 (IL‐27) inhibits central nervous system (CNS) inflammation is not clear. In this study we have investigated mechanisms that mitigate or curtail intraocular inflammation (uveitis) and examined whether inhibitory effects of IL‐27 are mediated locally by neuroretinal cells or by regulatory T cells. We show here that microglia cells in the neuroretina constitutively secrete IL‐27 and its expression is up‐regulated during uveitis. We further show that photoreceptors constitutively express IL‐27 receptor and respond to IL‐27 signalling by producing anti‐inflammatory molecules, IL‐10 and suppressor of cytokine signalling 1 (SOCS1) through signal transducer and activator of transcription 1 (STAT1) ‐dependent mechanisms. Moreover, STAT1‐deficient mice produced reduced amounts of IL‐27, IL‐10 and SOCS1 and developed more severe uveitis. Surprisingly, IL‐10‐producing regulatory T cells had marginal roles in suppressing uveitis. These results suggest that suppression of intraocular inflammation might be mediated through endogenous production of IL‐27 and IL‐10 by retinal cells, whereas SOCS proteins induced by IL‐27 during uveitis may function to protect the neuroretinal cells from the toxic effects of pro‐inflammatory cytokines. Targeted delivery of IL‐27 into immune privileged tissues of the CNS may therefore be beneficial in the treatment of CNS inflammatory diseases, such as uveitis and multiple sclerosis.

Suppressor of cytokine signaling-1 (SOCS1) inhibits lymphocyte recruitment into the retina and protects SOCS1 transgenic rats and mice from ocular inflammation.

PURPOSE Suppressors of cytokine signaling (SOCS) proteins regulate the intensity and duration of cytokine signals and defective expression of SOCS1 and SOCS3 has been reported in a number of human diseases. The purpose of this study was to investigate the role of SOCS1 in intraocular inflammatory diseases (uveitis) and whether SOCS1 expression is defective in patients with ocular inflammatory diseases. METHODS Blood from patients with scleritis or healthy human volunteers was analyzed for SOCS expression by RNase protection assay and RT-PCR. The authors generated SOCS1 transgenic rats and mice (SOCS1-Tg), induced experimental autoimmune uveoretinitis (EAU) by active immunization with interphotoreceptor retinal binding protein or adoptive transfer of uveitogenic T cells, and investigated effects of SOCS1 overexpression on EAU. SOCS1-mediated protection of retinal cells from apoptosis was assessed by annexin V staining. RESULTS Induction of cytokine-induced SH2 protein was comparable between patients and volunteers, whereas 80% of lymphocytes from patients with scleritis failed to induce SOCS1 in response to IL-2. Compared with wild-type littermates, SOCS1-Tg rats/mice developed less severe EAU. Constitutive overexpression of SOCS1 in retina inhibited expression of chemokines (CCL17, CCL20, CXCL9, CXCL10), reduced Th17/Th1 expansion, and inhibited recruitment of inflammatory cells into the retina. The authors also show that SOCS1 protected retinal cells from staurosporine as well as H₂O₂-induced apoptosis. CONCLUSIONS Defective expression of SOCS1 in patients with scleritis, taken together with SOCS1-mediated protection of neuroretinal cells from apoptosis, suggest that SOCS1 has neuroprotective function in the retina, implying that administration of SOCS1 mimetic peptides may be useful in treating uveitis or scleritis.

Interleukin 27 Induces the Expression of Complement Factor H (CFH) in the Retina

Complement factor H (CFH) is a central regulator of the complement system and has been implicated in the etiology of age-related macular degeneration (AMD), a leading cause of blindness in the elderly. In view of previous studies showing that reduced expression of CFH in the retina is a risk factor for developing AMD, there is significant interest in understanding how CFH expression is regulated in the retina. In this study, we have shown that the anti-inflammatory cytokine, IL-27, induced CFH expression in mouse retinal cells and human retinal pigmented epithelial cells (RPE) through STAT1-mediated up-regulation of Interferon Regulatory Factor-1 (IRF-1) and IRF-8. We further show that cells in the ganglion and inner-nuclear layers of the retina constitutively express IRF-1 and IRF-8 and enhanced CFH expression in the retina during ocular inflammation correlated with significant increase in the expression of IRF-1, IRF-8 and IL-27 (IL-27p28 and Ebi3). Our data thus reveal a novel role of IL-27 in regulating complement activation through up-regulation of CFH and suggest that defects in IL-27 signaling or expression may contribute to the reduction of CFH expression in the retina of patients with AMD.

Persistence of IL‐2 expressing Th17 cells in healthy humans and experimental autoimmune uveitis

Compared with other T‐helper subsets, Th17 cell numbers are very low in human blood but become elevated in chronic inflammatory diseases. In this study, we investigated mechanisms that may explain the frequent involvement of Th17 cells in autoimmune diseases such as uveitis. We compared Th17 and Th1 subsets and found that Th17 cells expressed lower IL‐2 levels during Ag‐priming and this correlated with their decreased susceptibility to activation‐induced cell death (AICD). However, complete depletion of IL‐2 with IL‐2 neutralizing antibodies rendered Th17 cells as susceptible to apoptosis as Th1 cells, suggesting that the low levels of IL‐2 produced by Th17 cells conferred survival advantages to this subset. We describe here a Th17 subtype that constitutively produces very low levels of IL‐2 (Th17‐DP). The Th17‐DP population increased dramatically in the blood and retina of mice during experimental autoimmune uveitis, indicating their potential involvement in the etiology of uveitis. We further show that the majority of the memory Th17 cells in human blood are Th17‐DP and are targets of daclizumab, an IL‐2R antibody used in treating recalcitrant uveitis. Thus, Th17 cells may persist in tissues and contribute to chronic inflammation by limiting IL‐2 production to levels that cannot provoke IL‐2‐induced AICD yet are sufficient to promote Th17 homeostatic expansion.