Inhibition of interleukin-2 messenger RNA in mouse lymphocytes by 2'-deoxycoformycin and adenosine metabolites

Adenosine acts through a novel extracellular receptor to inhibit granule exocytosis by natural killer cells

Adenosine concentrations in solid tumors are elevated as a result of altered metabolism by hypoxic cancer cells within the tumor microenvironment. In this study we show that adenosine inhibits mouse natural killer (NK) cell function by interfering with the process of granule exocytosis. Adenosine, at concentrations ranging from 5-25 microM, had a marked inhibitory effect on granule exocytosis by mouse spleen cells stimulated with phorbol myristate acetate and ionomycin. Selective depletion of spleen cell subsets by antibody and complement treatments established that granule exocytosis was mediated by NK cells. Blocking the cellular uptake of adenosine with NBTI or dilazep failed to prevent the inhibitory effect of adenosine, indicating the involvement of a cell-surface receptor. However, adenosine-induced inhibition of granule exocytosis was not blocked by the nonselective A1 and A2 receptor antagonists theophylline and 8-phenyltheophylline, the A1 receptor antagonist DPCPX, or the A2 receptor antagonist DMPX. In addition, the A3 receptor agonists APNEA and NECA failed to affect granule exocytosis. Taken together, these data provide evidence that adenosine inhibits NK cell granule exocytosis by interacting with a novel extracellular receptor. A similar inhibitory effect of tumor-elaborated adenosine on the function of NK cells and other cytotoxic lymphocytes may contribute to tumor survival in the face of host cell-mediated immune defenses.

Purine metabolism in feline lymphomas

Deficiency of the purine metabolic enzyme adenosine deaminase causes severe immunodeficiency. Retroviruses have been reported to decrease the activity of adenosine deaminase, and many retroviruses, including feline leukemia virus, cause immunodeficiency. Levels of purine metabolic enzymes including adenosine deaminase and consequences of adenosine deaminase inhibition were investigated in feline leukemia virus-infected fresh tumor cells and infected and uninfected cell lines. No evidence of virus effect on levels of adenosine deaminase or other purine metabolic enzymes was detected. Neoplastic cells demonstrated considerable heterogeneity of activity levels of purine metabolic enzymes.

Defective cAMP-dependent phosphorylation of intact T lymphocytes in active systemic lupus erythematosus

The present study was undertaken to establish whether cAMP-dependent phosphorylation of endogenous substrates is impaired in T lymphocytes from subjects with active systemic lupus erythematosus (SLE). In normal human T lymphocytes, the cell-permeable cAMP analog, N6,O2'-dibutyryladenosine 3',5'-cyclic monophosphate, induced phosphorylation of substrates with molecular masses of 17.5, 23/25, 33.5 kDa on one-dimensional SDS/PAGE. Maximal phosphorylation occurred at 60 min. In contrast to healthy T cells, the extent of substrate phosphorylation achieved in active SLE T cells (n = 8) was only 15% at 60 min in the 17.5-kDa substrate, 21% in the 23/25-kDa substrate, and 9% in the 33.5-kDa substrate. The rheumatic disease controls (rheumatoid arthritis; primary Sjögren syndrome; n = 8) exhibited a mean 72%, 124%, and 85%, respectively, of phosphorylation observed in healthy T cells. Because the only known mechanism by which cAMP acts is via cAMP-dependent protein kinase (protein kinase A), these data raise the possibility of a defect at the level of this kinase in SLE T lymphocytes.