ADA

Adenosine deaminase (ADA) is an enzyme of purine metabolism catalyzing irreversible deamination of adenosine to inosine, and deoxyadenosine to deoxyinosine, respectively.ADA has two major isoenzymes ADA1 (a single-chain Zn-binding protein and almost all activities are attributed to this protein) and ADA2 (believed to be produced by monocytes and is found in negligible quantities). ADA is widely distributed in human tissues with its highest activity in T-lymphocytes than B lymphocytes and increases during T cell differentiation. It also acts in maturation of monocytes transforming them to macrophage. It is considered as a good marker of cell-mediated immune response. High lymphocytic ADA activities were reported in many diseases which are associated with alteration in cell mediated immune responses.
ADA has been proposed to be a useful surrogate marker for TB because it can be detected in body fluids such as pleural, pericardial and peritoneal fluids. The levels of ADA increase in TB because of the stimulation of T cells by mycobacterial antigens. High titre of ADA in pleural effusion is an indicator of pleural tuberculosis and necessity of treatment initiation. On the other hand it is used for treatment follow up in patient on standard anti-tuberculosis regimen. Decreasing level of ADA could be a predictor of treatment response.