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Journal of Clinical Investigation (1)
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Apasov, Sergey (1)
Apasov, Sergey G. (1)
Blackburn, Michael R. (1)
Choukèr, Alexander (1)
Kaufmann, Ines (1)
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Sitkovsky, Michail V. (1)
Smith, Patrick T. (1)
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Ward, Jerrold M (1)
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Critical Role of Hypoxia and A2A Adenosine Receptors in Liver Tissue-Protecting Physiological Anti-Inflammatory Pathway
Ward, Jerrold M
Sitkovsky, Michail V
Whole body exposure of wild type control littermates and A2A adenosine receptor (A2AR) gene deleted mice to low oxygen containing inspired gas mixture allowed the investigation of the mechanism that controls inflammatory liver damage and protects the liver using a mouse model of T cell-mediated viral and autoimmune hepatitis. We tested the hypothesis that the inflammatory tissue damage-associated hypoxia and extracellular adenosine → A2AR signaling plays an important role in the physiological anti-inflammatory mechanism that limits liver damage during fulminant hepatitis. After induction of T cell-mediated hepatitis, mice were kept in modular chambers either under normoxic (21% oxygen) or hypoxic (10% oxygen) conditions for 8 h. It was shown that the whole body exposure to hypoxic atmosphere caused tissue hypoxia in healthy animals as evidenced by a decrease in the arterial blood oxygen tension and increase of the plasma adenosine concentration (P < 0.05). This “hypoxic” treatment resulted in significantly reduced hepatocellular damage and attenuated levels of serum cytokines in mice with acute liver inflammation. The anti-inflammatory effects of hypoxia were not observed in the absence of A2AR in studies of A2AR gene-deficient mice or when A2AR have been pharmacologically antagonized with synthetic antagonist. The presented data demonstrate that total body hypoxia-triggered pathway provides protection in acute hepatitis and that hypoxia (upstream) and A2AR (downstream) function in the same immunosuppressive and liver tissue-protecting pathway.
Adenosine deaminase deficiency increases thymic apoptosis and causes defective T cell receptor signaling
Blackburn, Michael R.
Kellems, Rodney E.
Smith, Patrick T.
Sitkovsky, Michail V.
Journal of Clinical Investigation
Adenosine deaminase (ADA) deficiency in humans results in a severe combined immunodeficiency (SCID). This immunodeficiency is associated with severe disturbances in purine metabolism that are thought to mediate lymphotoxicity. The recent generation of ADA-deficient (ADA–/–) mice has enabled the in vivo examination of mechanisms that may underlie the SCID resulting from ADA deficiency. We demonstrate severe depletion of T and B lymphocytes and defects in T and B cell development in ADA–/– mice. T cell apoptosis was abundant in thymi of ADA–/– mice, but no increase in apoptosis was detected in the spleen and lymph nodes of these animals, suggesting that the defect is specific to developing thymocytes. Studies of mature T cells recovered from spleens of ADA–/– mice revealed that ADA deficiency is accompanied by TCR activation defects of T cells in vivo. Furthermore, ex vivo experiments on ADA–/– T cells demonstrated that elevated adenosine is responsible for this abnormal TCR signaling. These findings suggest that the metabolic disturbances seen in ADA–/– mice affect various signaling pathways that regulate thymocyte survival and function. Experiments with thymocytes ex vivo confirmed that ADA deficiency reduces tyrosine phosphorylation of TCR-associated signaling molecules and blocks TCR-triggered calcium increases.
J. Clin. Invest. 108:131–141 (2001). DOI:10.1172/JCI200110360.
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