Adenosine inhibits IL-12 and TNF-alpha production via adenosine A(2a) receptor-dependent and independent mechanisms

Interleukin 12 (IL-12) is a crucial cytokine in the regulation of T helper 1 vs. T helper 2 immune responses. In the present study, we investigated th e effect of the endogenous purine nucleoside adenosine on the production of IL-12, In mouse macrophages, adenosine suppressed 12,12 production. Althou gh the order of potency of adenosine receptor agonists suggested the involv ement of A(2a) receptors, data obtained with A(2a) receptor-deficient mice showed that the adenosine suppression of IL-12 and even TNF-alpha productio n is only partly mediated by A(2a) receptor ligation. Studies with adenosin e receptor antagonists or the adenosine uptake blocker dipyridamole showed that adenosine released endogenously also decreases IL-12. Although adenosi ne increases IL-10 production, the inhibition of IL-12 production is indepe ndent of the increased IL-10. The mechanism of action of adenosine was not associated with alterations of the activation of the p38 and p42/p44 mitoge n-activated protein kinases or the phosphorylation of the c-Jun terminal ki nase. Adenosine failed to affect steady-state levels of either IL-12 p35 or p40 mRNA, but augmented IL-10 mRNA levels. In summary, adenosine inhibits IL-12 production via various adenosine receptors. These results support the notion that adenosine-based therapies might be useful in certain autoimmun e and/or inflammatory diseases.