High common-γ cytokine receptor levels promote expression of Interleukin-2/Interleukin-7 receptor α-chains with implications on T-cell differentiation and function.

Cytokines of the common-γ receptor chain (γc) family are crucial for T-cell differentiation and dysregulation of γc cytokine pathways is involved in the pathogenesis of autoimmune diseases. There is increasing evidence that the availability of the γc receptor (CD132) for the associated receptor chains has implications for T-cell functions. Here we studied the influence of differential γc expression on the expression of the IL-2Rα (CD25), the IL-7Rα (CD127) and the differentiation of activated naïve T cells. We fine-tuned the regulation of γc expression in human primary naïve T cells by lentiviral transduction using small hairpin (sh)RNAs and γc cDNA. Differential γc levels were then analysed for effects on T-cell phenotype and function after activation. Differential γc expression markedly affected IL-2Rα and IL-7Rα expression on activated naïve T cells. High γc expression (γc-high) induced significantly higher expression of IL-2Rα and re-expression of IL-7Rα after activation. Inhibition of γc caused lower IL-2Rα/IL-7Rα expression and impaired proliferation of activated naïve T cells. In contrast, γc-high T cells secreted significantly higher concentrations of effector cytokines (i.e., IFN-γ, IL-6) and showed higher cytokine-receptor induced STAT5 phosphorylation during initial stages as well as persistently higher pSTAT1 and pSTAT3 levels after activation. Finally, accelerated transition towards a CD45RO expressing effector/memory phenotype was seen especially for CD4+ γc-high naïve T cells. These results suggested that high expression of γc promotes expression of IL-2Rα and IL-7Rα on activated naïve T cells with significant effects on differentiation and effector cytokine expression.

Blockade of CD127 Exerts a Dichotomous Clinical Effect in Marmoset Experimental Autoimmune Encephalomyelitis.

Non-human primate models of human disease have an important role in the translation of a new scientific finding in lower species into an effective treatment. In this study, we tested a new therapeutic antibody against the IL-7 receptor α chain (CD127), which in a C57BL/6 mouse model of experimental autoimmune encephalomyelitis (EAE) ameliorates disease, demonstrating an important pathogenic function of IL-7. We observed that while the treatment was effective in 100 % of the mice, it was only partially effective in the EAE model in common marmosets (Callithrix jacchus), a small-bodied Neotropical primate. EAE was induced in seven female marmoset twins and treatment with the anti-CD127 mAb or PBS as control was started 21 days after immunization followed by weekly intravenous administration. The anti-CD127 mAb caused functional blockade of IL-7 signaling through its receptor as shown by reduced phosphorylation of STAT5 in lymphocytes upon stimulation with IL-7. Group-wise analysis showed no significant effects on the clinical course and neuropathology. However, paired twin analysis revealed a delayed disease onset in three twins, which were high responders to the immunization. In addition, we observed markedly opposite effects of the antibody on pathological changes in the spinal cord in high versus low responder twins. In conclusion, promising clinical effect of CD127 blockade observed in a standard inbred/SPF mouse EAE model could only be partially replicated in an outbred/non-SPF non-human primate EAE model. Only in high responders to the immunization we found a positive response to the treatment. The mechanism underpinning this dichotomous response will be discussed.

Interleukin-2 signalling is modulated by a labile disulfide bond in the CD132 chain of its receptor.

Certain disulfide bonds present in leucocyte membrane proteins are labile and can be reduced in inflammation. This can cause structural changes that result in downstream functional effects, for example, in integrin activation. Recent studies have shown that a wide range of membrane proteins have labile disulfide bonds including CD132, the common gamma chain of the receptors for several cytokines including interleukin-2 and interleukin-4 (IL-2 and IL-4). The Cys(183)-Cys(232) disulfide bond in mouse CD132 is susceptible to reduction by enzymes such as thioredoxin (TRX), gamma interferon-inducible lysosomal thiolreductase and protein disulfide isomerase, which are commonly secreted during immune activation. The Cys(183)-Cys(232) disulfide bond is also reduced in an in vivo lipopolysaccharide (LPS)-induced acute model of inflammation. Conditions that lead to the reduction of the Cys(183)-Cys(232) disulfide bond in CD132 inhibit proliferation of an IL-2-dependent T cell clone and concomitant inhibition of the STAT-5 signalling pathway. The same reducing conditions had no effect on the proliferation of an IL-2-independent T cell clone, nor did they reduce disulfide bonds in IL-2 itself. We postulate that reduction of the Cys(183)-Cys(232) disulfide in CD132 inhibits IL-2 binding to the receptor complex. Published data show that the Cys(183)-Cys(232) disulfide bond is exposed at the surface of CD132 and in close contact with IL-2 and IL-4 in their respective receptor complexes. In addition, mutants in these Cys residues in human CD132 lead to immunodeficiency and loss of IL-2 binding. These results have wider implications for the regulation of cytokine receptors in general, as their activity can be modulated by a 'redox regulator' mechanism caused by the changes in the redox environment that occur during inflammation and activation of the immune system.