Human adenosine deaminases control the immune cell responses to activation signals by reducing extracellular adenosine concentration

Abstract Adenosine rapidly accumulates in the sites of inflammation and tumor growth. It binds to adenosine receptors expressed on the cell surface of immune cells and induces either suppression or activation of inflammatory responses to pathogens. In humans the level of extracellular adenosine is regulated by two adenosine deaminases ADA1 and ADA2. Decrease in ADAs concentration due to genetic defects in the ADA genes leads to serious perturbation in the immune system function while increase in ADA activity associates with numerous immune diseases and cancers. The immune responses to extracellular adenosine have largely been studied using pharmacological approach where non-hydrolysable adenosine receptors agonists substitute adenosine to form the activated state of adenosine receptors. On contrary, adenosine receptors bound to adenosine receptor antagonists mimic inactivated state of adenosine receptors. Here, the effect of adenosine receptor agonists and antagonists on the monocytes function as well as and T helper cell proliferation and differentiation was compared with the effect of adenosine and adenosine deaminases. It was demonstrated that adenosine deaminases control the immune cells responses to activation signals by reducing the concentration of extracellular adenosine and that the cells sensitivity to adenosine greatly depends on the type of the cell activation. Therefore, our data suggests that ADAs could be considered as new drug candidates for the treatment of immune disorders and cancers.