Differential effects of interleukin-13 and interleukin-6 on Jak/STAT signaling and cell viability in pancreatic ß-cells.

Pro-inflammatory cytokines are important mediators of ß-cell demise in type 1 diabetes, and similar mechanisms are increasingly implicated in type 2 diabetes, where a state of chronic inflammation may persist. It is likely that the actions of anti-inflammatory cytokines are also altered in diabetes. Cytokines are released from immune cells, which may be recruited to the islets in diabetes, but they can also be produced by islet endocrine cells in response to environmental factors, including enteroviral infection. Since enteroviral infection of islet cells may influence the development of diabetes in humans, we examined the actions of two cytokines, IL-13 and IL-6, whose expression are reported to be altered in ß-cells during enteroviral infection. Human and rodent islet cells were shown to express receptors for both IL-13 and IL-6, and treatment with either cytokine resulted in the rapid phosphorylation of STAT3 and STAT6. However, while ß-cells were protected against a range of cytotoxic insults during exposure to IL-13, treatment with IL-6 enhanced cytotoxicity and western blotting revealed that IL-13 induced one specific isoform of phospho-STAT6 preferentially. Upon incubation with both cytokines together, the isoform of STAT6 that was upregulated by IL-13 alone was again induced, and the effects of IL-6 on ß-cell viability were attenuated. Overall, the results suggest that induction of specific isoforms of STAT family transcription factors may underlie the cytoprotective actions of IL-13, and they imply that selective targeting of specific STAT-mediated signaling components could provide a means to ameliorate the loss of ß-cell viability in diabetes.

Erythropoietin resistance: the role of inflammation and pro-inflammatory cytokines.

Up to 10% of patients with renal disease receiving recombinant human erythropoietin (rHuEPO) therapy show poor responsiveness to the drug. Even in patients who do respond to rHuEPO, there is a marked variability in drug sensitivity. Several factors have been recognized as causing resistance to rHuEPO, notably iron deficiency, infection/inflammation, and under dialysis. However, when these factors are excluded, the wide variation in responsiveness to rHuEPO persists. The mechanism of this effect needs to be fully elucidated. One hypothesis is that patients with uraemia showing resistance to rHuEPO may have enhanced levels of immune activation, causing increased release of pro-inflammatory cytokines in the bone marrow. Uraemia is known to be a chronic inflammatory state, with some patients showing considerably increased laboratory markers of inflammation and immune activation. Chronic inflammation can modify the process of erythropoiesis, probably mediated via pro-inflammatory cytokines such as interleukin-1 (IL-1), tumour necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma). The concept that rHuEPO resistance is due to enhanced levels of immune activity has been investigated by studying T-cell phenotypes using flow cytometry, as well as cytokine release from T cells and monocytes in 'good' and 'poor' responders to rHuEPO. Poor responders had significantly reduced CD28 expression on both CD4+ and CD8+ cells, enhanced IL-10 generation from peripheral blood mononuclear cells (PBMCs), higher plasma IL-12 levels, and increased TNF-alpha and IFN-gamma release from PBMCs. Anti-cytokine antibodies may be useful for studying inflammatory cytokine secretion from T cells in patients with renal failure. Strategies utilizing anti-cytokine therapy may prove to be a useful adjuvant in optimizing the response to rHuEPO therapy.

Increased expression of erythropoiesis inhibiting cytokines (IFN-gamma, TNF-alpha, IL-10, and IL-13) by T cells in patients exhibiting a poor response to erythropoietin therapy.

Resistance to recombinant human erythropoietin occurs in a small but important proportion of hemodialysis patients. This may be due to increased immune activation because pro-inflammatory cytokines inhibit erythropoiesis in vitro. Using FACScan flow cytometry, the proportion of PMA/ionomycin-stimulated T cells expressing cytokines ex vivo was compared in 18 poor responders to erythropoietin, 14 good responders to erythropoietin, and 14 normal controls. CD4(+) T cells from poor responders expressed more interferon-gamma (IFN-gamma; 19 +/- 6%) compared with good responders (11 +/- 6%, P < 0.001) and controls (12 +/- 6%, P < 0.01). Similarly, CD4+ T cells from poor responders expressed more tumor necrosis factor-alpha (TNF-alpha; poor responders: 51 +/- 19% versus good responders: 27 +/- 15% [P < 0.01] and controls: 30 +/- 19% [P < 0.01]). CD4+ expression of IL-10 was also enhanced (poor responders: 1.6 +/- 1.1% versus good responders: 0.7 +/- 0.6% [P < 0.05] and controls: 0.5 +/- 0.2% [P < 0.01]). Likewise, CD4+ expression of interleukin-13 (IL-13) was increased (poor responders: 4.4 +/- 4.2% versus good responders: 1.6 +/- 1.7% [P < 0.05] and controls: 1.6 +/- 1.5% [P < 0.05]). CD8+ T cells from poor responders also showed enhanced expression of cytokines. For IFN-gamma, poor responder expression was 48 +/- 20% compared with 31 +/- 17% (P < 0.05) for good responders and 23 +/- 15% (P < 0.01) for controls. TNF-alpha expression for poor responders was 41 +/- 21% versus 25 +/- 14% for good responders (P < 0.05) and 21 +/- 15% for controls (P < 0.01). IL-10 expression for poor responders was 2.0 +/- 1.2% (good responders: 0.7 +/- 0.6% [P < 0.01]; controls: 0.5 +/- 0.2% [P < 0.001]). These data indicate that T cells from poor responders are in an enhanced activation state possibly as a result of chronic inflammation. In the absence of any other cause (such as iron deficiency), the overproduction of cytokines may account for hyporesponsiveness to erythropoietic therapy in patients with renal failure.

Poor response to recombinant erythropoietin is associated with loss of T-lymphocyte CD28 expression and altered interleukin-10 production.

BACKGROUND: Recombinant erythropoietin (Epo) therapy is well established as an effective treatment for the anaemia of end-stage renal disease. However, 5-10% of such patients do not respond adequately and an important contributory factor to this is chronic inflammation. METHODS: The present study compares the circulating T-cell phenotypes of haemodialysis patients who respond poorly to Epo with those who respond well, along with normal controls. Isolated peripheral blood mononuclear cells were labelled with immunofluorescent monoclonal antibodies to surface antigens and analysed by flow cytometry. In vitro mononuclear cell cytokine secretion was also studied in the three subject groups. The cells were cultured for 48 h either without stimulus, with lipopolysaccharide or with monoclonal antibodies to CD3 and CD28. RESULTS: C-reactive protein levels were increased in poor responders to Epo (18.6 +/- 20.7 mg/l) compared with good responders (8.7 +/- 8.0 mg/l) and normal controls (3.8 +/- 1.1 mg/l). Patients responding poorly to Epo had increased circulating levels of CD4+/CD28- and CD8+/CD28- T-cells compared with patients responding well to Epo and normal controls. Unstimulated mononuclear cells from poor responders showed increased in vitro generation of interleukin-10 (IL-10) compared with both patients responding well to Epo and normal controls. Additionally, IL-10 generation stimulated by monoclonal antibodies to CD3 and CD28 was increased in poor responders compared with normal controls. CONCLUSIONS: These findings suggest that patients responding poorly to Epo may show enhanced immune activation as manifest by changes in both T-cell function and phenotype.