The plant hormone zeatin riboside inhibits T lymphocyte activity via adenosine A2A receptor activation (IRM6P.710)

Cytokinins are plant hormones that play an integral role in multiple aspects of plant growth and development. The biological functions of cytokinins in mammalian systems are, however, largely uncharacterized. The naturally occurring cytokinin zeatin riboside has recently been demonstrated to activate the mammalian adenosine A2A receptor, which is broadly expressed by various cell types including immune system cells, with the activation of the A2AR playing a role in the regulation of cells involved in both innate and adaptive immunity. We show for the first time that zeatin riboside modulates mammalian immune system activity via an A2AR-dependent mechanism. Specifically, zeatin riboside inhibits the production by CD3+CD4+ T cells of IFN-γ, IL-2, TNF-α, IL-4 and IL-13, and the production by CD3+CD8+ T cells of IFN-γ, IL-2, and TNF-α. Additionally, the upregulation of CD25, CD69 and CD40L by activated T lymphocytes is modulated by zeatin riboside. The immunomodulatory activities of zeatin riboside are blocked by co-treatment with the selective A2AR antagonist ZM241385. These data suggest that zeatin riboside possesses therapeutic potential as a mammalian immunomodulatory agent.

Adenosine A2A receptor activation inhibits T cell activity in a murine model of chronic granulomatous disease (87.3)

Chronic granulomatous disease (CGD) is caused by defects in the NADPH oxidase system, and is characterized by an increased susceptibility to recurrent, severe bacterial and fungal infections. Early diagnosis and aggressive treatment can be effective at combating life threatening infections, but other significant complications of CGD, such as non-infectious hyperinflammatory manifestations, result in a high associated morbidity. Recent studies suggest that the hyperinflammation observed in CGD (gp91phox deficient) mice may be due in part to dysregulated T cell activity. We have broadly characterized the phenotypes of T lymphocytes collected from p91phox deficient mice and our data indicate that although the basal activation states of T cells collected from WT and CGD mice are similar, upon activation through the T cell receptor, CGD T cells produce higher levels of the pro-inflammatory cytokines IFN-γ and IL-2 and express elevated levels of the cell surface activation markers CD25, CD69 and CD40L as compared to WT T cells. This hyper-activation of CGD T cells is effectively modulated by treatment with the selective adenosine A2A receptor agonist CGS21680, which reduces the levels of IFN-γ and IL-2 by approximately 90% and down regulates CD25, CD69 and CD40L expression by approximately 50%. These data suggest that the adenosine A2A receptor is a potential pharmacological target for the treatment of the hyperinflammatory complications observed in CGD patients.

Sphingosine-1-phosphate reduces CD4+ T-cell activation in type 1 diabetes through regulation of hypoxia-inducible factor short isoform I.1 and CD69

OBJECTIVES

Non-obese diabetic (NOD) mice develop spontaneous type 1 diabetes. We have shown that sphingosine-1-phosphate (S1P) reduces activation of NOD diabetic endothelium via the S1P1 receptor. In the current study, we tested the hypothesis that S1P could inhibit CD4(+) T-cell activation, further reducing inflammatory events associated with diabetes.

RESEARCH DESIGN AND METHODS

CD4(+) T-cells were isolated from diabetic and nondiabetic NOD mouse splenocytes and treated in the absence or presence of S1P or the S1P1 receptor-specific agonist, SEW2871. Lymphocyte activation was examined using flow cytometry, cytokine bead assays, and a lymphocyte:endothelial adhesion assay.

RESULTS

Diabetic T-cells secreted twofold more gamma-interferon (IFN-gamma) and interleukin-17 than nondiabetic lymphocytes. Pretreatment with either S1P or SEW2871 significantly reduced cytokine secretion by approximately 50%. Flow cytometry analysis showed increased expression of CD69, a marker of lymphocyte activation, on diabetic T-cells. Both S1P and SEW2871 prevented upregulation of CD69 on CD4(+) cells. Quantitative RT-PCR showed that lymphocytes from diabetic NOD mice had 2.5-fold lower hypoxia-inducible factor (HIF)-1alpha short isoform I.1 (HIF1alphaI.1) mRNA levels than control. HIF1alphaI.1 is a negative regulator of lymphocyte activation. S1P significantly increased HIF1alpha I.1 mRNA levels in both control and diabetic groups. IFN-gamma production and surface CD69 expression was significantly increased in lymphocytes of HIF1alphaI.1-deficient mice. S1P did not reduce either CD69 or IFN-gamma expression in lymphocytes from HIF1alphaI.1-deficient mice.

CONCLUSIONS

S1P acts through the S1P1 receptor and HIF1alpha I.1 to negatively regulate T-cell activation, providing a potential therapeutic target for prevention of diabetes and its vascular complications.

Genome sequence of the plant pathogen and biotechnology agent Agrobacterium tumefaciens C58

Agrobacterium tumefaciens is a plant pathogen capable of transferring a defined segment of DNA to a host plant, generating a gall tumor. Replacing the transferred tumor-inducing genes with exogenous DNA allows the introduction of any desired gene into the plant. Thus, A. tumefaciens has been critical for the development of modern plant genetics and agricultural biotechnology. Here we describe the genome of A. tumefaciens strain C58, which has an unusual structure consisting of one circular and one linear chromosome. We discuss genome architecture and evolution and additional genes potentially involved in virulence and metabolic parasitism of host plants.