An immunomorphologic study of adenosine deaminase distribution in human thymus tissue, normal lymphocytes, and hematopoietic cell lines.

Adenosine deaminase (ADA) has been detected immunohistochemically in human thymus. The enzyme was localized predominantly in cortical thymocytes. Occasional lymphocytes in the medulla were also positive for ADA. Blood vessels, connective tissue, and Hassall's corpuscles were not stained for the enzyme. Using single-cell immunofluorescence and immunoperoxidase assays, we found that thymocytes and lymphoid cells of peripheral blood (PBL) and tonsils were heterogeneous with respect to ADA expression. About 70% of thymocytes were strongly stained for the enzyme whereas weak staining was seen in 20% of cells. About 10% of thymocytes were ADA negative. Twenty percent of PBL and tonsil cells were strongly positive for ADA, 10% of cells were negative for the enzyme, and weak staining was seen in the remainder. Bone marrow mononuclear cells were not stained for ADA. One hundred percent of lymphoblasts of 3 T cells leukemia lines were strongly stained for the enzyme whereas weak staining was seen in a pre-B cell leukemia line, 4 B cell lymphoma/normal lines, 2 non-T, non-B cell leukemia lines and 2 myeloid cell leukemia lines. There was a good correlation between intensity of cellular staining and quantity and activity of ADA detected in cell extracts by radioimmunoassay and enzymatically. The development of immunomorphologic methods for the detection of ADA provides a tool to study the role of the enzyme in function(s) and differentiation of normal and leukemic cells.