[Adenosine deaminase isoenzymes in patients with Graves' disease]

CD26, the T cell activation antigen, is identical to the ADA binding protein and is considered to interact with ADA to activate the T cells on the surface. Therefore, we examined the activity of serum ADA isoenzymes in patients with Graves' disease in whom CD26 presented T cells were increased. The activities of total ADA and ADA2 were significantly higher in Graves' disease than normals. We also observed that the levels of soluble interleukin-2 receptor (sIL-2R) and neopterin, markers of T cell activation, were significantly higher in Graves' disease. The correlation coefficients among ADA2, neopterin, and sIL-2R were significantly high (p < 0.001). Among these parameters, only sIL-2R was correlated with the thyroid hormones. ADA2 activity was considered to reflect the activated state of T cells and to be, independent of the thyroid hormone levels.