Reciprocal effects of IFN-beta and IL-12 on STAT4 activation and cytokine induction in T cells.

IL-12 is an immunoregulatory cytokine, which promotes Th1 cell differentiation and is a major inducer of IFN-gamma. IFN-beta, a Type I IFN used in the treatment of multiple sclerosis, has been shown to significantly increase the expression of the anti-inflammatory cytokine IL-10, a major suppressor of Th1 cytokines. The beneficial immunomodulatory effects of IFN-beta may in part be a result of its ability to suppress IL-12. However, IL-12 and IFN-beta signal via the STAT4 pathway. Our aim was to investigate the relationship between IL-12 and IFN-beta by observing the effect of prior exposure to IL-12 or IFN-beta on the ability of T cells to subsequently respond to the other cytokine. We report that IFN-beta increases IL-12-induced STAT4 phosphorylation and up-regulates IL-12 receptor beta1 and beta2 expression. However, despite this up-regulation, IFN-beta suppressed IL-12-induced IFN-gamma expression. Our results suggest that this may be a result of the parallel induction of IL-10 by IFN-beta.

Effects of glucocorticoids on STAT4 activation in human T cells are stimulus-dependent.

Glucocorticoids affect the immune system by a number of mechanisms, including modulation of cytokine production in lymphocytes. Glucocorticoids suppress T helper cell type 1 immune responses by decreasing the ability of T cells to respond to interleukin (IL)-12, a major inducer of interferon (IFN)-gamma. IFN-beta increases the expression of the anti-inflammatory cytokine IL-10 and suppresses IL-12. Signaling pathways through IFN-beta and the IL-12 receptor (IL-12R) involve activation by phosphorylation of signal transducer and activator of transcription 4 (STAT4). Our aim was to investigate the effects of dexamethasone on STAT4 activation by IFN-beta and IL-12 in human T cell blasts. We report that dexamethasone decreases IL-12-induced STAT4 phosphorylation and IFN-gamma production and enhances IFN-beta-induced STAT4 activation and IL-10 production. These effects are associated with a down-regulation of IL-12Rbeta1 expression but an up-regulation of IFN-betaR. These results indicate that the effect of glucocorticoids on the STAT4 signaling pathway depends on the stimulus activating that pathway.

Reciprocal Regulation of Substance P and IL-12/IL-23 and the Associated Cytokines, IFNγ/IL-17: A Perspective on the Relevance of This Interaction to Multiple Sclerosis.

UNLABELLED: The neuropeptide substance P (SP) exhibits cytokine-like properties and exerts different effects in autoimmune inflammation. Various immune cells express SP and its neurokinin-1 receptor (NK1R) isoforms. A role for SP has been demonstrated in a number of autoimmune conditions, including multiple sclerosis (MS). In this work, we studied the role of SP and NK1R in human immune cells with a focus on their relationship with IL-12/IL-23 family cytokines and the associated IFN-γ/IL-17. AIMS: (1) To determine the role of SP mediated effects on induction of various inflammatory cytokines in peripheral blood mononuclear cells (PBMC); (2) to investigate the expression of SP and its receptor in T cells and the effects of stimulation with IL-12 and IL-23. Quantitative real-time PCR, flow cytometry, ELISA, promoter studies on PBMC and primary T cells from healthy volunteers, and Jurkat cell line. Treatment with SP significantly increased the expression of IL-12/IL-23 subunit p40, IL-23 p19 and IL-12 p35 mRNA in human PBMC. Expression of NK1R and SP in T cells was upregulated by IL-23 but a trend was observed with IL-12. The IL-23 effect likely involves IL-17 production that additionally mediates IL-23 effects. Mutual interactions exist with SP enhancing the cytokines IL-23 and IL-12, and SP and NK1R expression being differentially but potentially synergistically regulated by these cytokines. These findings suggest a proinflammatory role for SP in autoimmune inflammation. We propose a model whereby immunocyte derived SP stimulates Th1 and Th17 autoreactive cells migrating to the central nervous system (CNS), enhances their crossing the blood brain barrier and perpetuates inflammation in the CNS by being released from damaged nerves and activating both resident glia and infiltrating immune cells. SP may be a therapeutic target in MS.

IL-12 inhibits glucocorticoid-induced T cell apoptosis by inducing GMEB1 and activating PI3K/Akt pathway.

Interleukin (IL)-12 is an important pro-inflammatory cytokine that has been shown to play a role in T cell survival, at least in part by activating the PI3K/Akt pathway. Glucocorticoid modulatory element binding protein (GMEB)1 and 2 are closely related proteins that modify the glucocorticoid receptor binding locus and thus modulate glucocorticoid-mediated gene induction effects, including apoptosis. GMEB1 associates with caspases and prevents apoptosis of cells in the nervous system. We have observed, in preliminary studies, that IL-12 up-regulates GMEB mRNA in human T cells, and postulated that this may contribute to the anti-apoptotic effect of IL-12 on T cells, in particular with regard to glucocorticoid induced apoptosis. Here, we confirm that IL-12 rescue of dexamethasone induced T cell apoptosis involves the PI3K/Akt pathway and that IL-12 induces GMEB1 and GMEB2. A siRNA knockdown of GMEB1 reverses the protective effect of IL-12 on dexamethasone induced T cell apoptosis. Thus, IL-12 protects T cells from glucocorticoid induced apoptosis via PI3K/Akt pathway and via induction of GMEB1, which is likely to reduce transactivation of the glucocorticoid receptor and induction of apoptotic genes. As glucocorticoid induced apoptosis occurs both in physiological and pathological/therapeutic situations, and IL-12 is actively involved in a variety of inflammatory and immune responses, the ability of IL-12 to inhibit steroid responses and increase T cell survival through GMEB1 has wide ranging implications. Manipulating GMEB may be used therapeutically to enhance the resistance or the sensitivity to steroids.

Orexin A (hypocretin-1) levels are not reduced while cocaine/amphetamine regulated transcript levels are increased in the cerebrospinal fluid of patients with multiple sclerosis: no correlation with fatigue and sleepiness.

BACKGROUND: Fatigue and sleep disturbance are common features of multiple sclerosis (MS). Our objectives were to determine cerebrospinal fluid levels of orexin A (hypocretin-1), a hypothalamic peptide involved in sleep, in patients with MS, and correlate them with fatigue, sleepiness, and levels of cocaine and amphetamine regulated transcript (CART) another neuropeptide regulating metabolism with wider nervous system distribution. METHODS: Consecutive patients with MS (n=34), other inflammatory (n=24) or non-inflammatory (n=42) neurological diseases, undergoing lumbar puncture were investigated. Orexin and CART were measured by RIA by investigators unaware of the patients' diagnosis. RESULTS: Orexin A was slightly decreased in the cerebrospinal fluid of patients with inflammatory disease. There was no evidence of orexin A deficiency in MS, although there was a non-significant trend toward a decrease compared to non-inflammatory neurological diseases (p=0.06). CART levels were increased in MS compared to the non-inflammatory disease group (p=0.03). There were no significant correlations between CSF levels of orexin A and CART, fatigue, and hypersomnolence. CONCLUSIONS: Cerebrospinal fluid orexin A is decreased in CNS inflammatory diseases other than MS, where it shows a trend toward reduction, but does not correlate significantly with CART or with measures of fatigue and hypersomnolence.

Curcumin modulation of IFN-beta and IL-12 signalling and cytokine induction in human T cells.

Curcumin is a polyphenol derived from the dietary spice turmeric. It possesses diverse anti-inflammatory and anti-cancer properties. Curcumin has been shown to exhibit an inhibitory effect on the production of inflammatory cytokines by human monocytes and has inhibited the animal model of multiple sclerosis (MS), experimental autoimmune encephalomyelitis (EAE) in association with a decrease in interleukin 12 (IL-12) production and signal transducer and activator of transcription 4 (STAT4) activation. The type I interferon (IFN) IFN-has the ability to suppress IL-12. Both IL-12 and IFN-alpha/beta signal through the activation by phosphorylation of STAT4. Our aim was to investigate the effects of curcumin on the ability of T cells to respond to IL-12 or IFN-alpha/beta. We report that curcumin decreases IL-12-induced STAT4 phosphorylation, IFN-gamma production, and IL-12 Rbeta1 and beta2 expression. IFN-beta-induced STAT4 phosphorylation, IL-10 production and IFN receptor (IFNAR) subunits 1 and 2 expression were enhanced by curcumin. Curcumin increased IFN-alpha-induced IL-10 and IFNAR1 expression. Prior exposure to curcumin decreased IFN-alpha-induced IFNAR2 expression and did not modify the level of IFN-alpha-induced pSTAT4 generation. Thus, the effect of curcumin on STAT4 activation in T cells is dependent upon the stimulus to which the T cells have been exposed.