High concentration of adenosine in human visceral leishmaniasis despite increased ADA and decreased CD73

Absence of an effective Th-1 response has been demonstrated as a major cause for the disease pathology among patients with visceral leishmaniasis (VL). Defining strategies to prevent the development of Th-2 response and/or initiate/activate effective Th-1 response may be of help to reduce the growing incidence of drug unresponsiveness. Adenosine, which is considered as an endogenous anti-inflammatory agent is generated in injured/inflamed tissues by the enzymatic catabolism of adenosine triphosphate (ATP), and it suppresses inflammatory responses of essentially all immune cells. The extracellular adenosine-producing pathway comprises two major enzymes CD39 (ATP -> ADP -> AMP) and CD73 (AMP -> Adenosine). In contrast, the adenosine-degrading pathway contains only one major enzyme adenosine deaminase (ADA). Our study shows high concentration of adenosine in diseased condition, varying expression of enzyme involved in adenosine-producing (CD73 down arrow) and adenosine-degrading (ADA up arrow) pathways. These are less studied in infections like VL but are very important in terms of endogenous regulation of immune response among patients.