Distribution of 5′-nucleotidase in Human Lymphoid Tissues

Low activity of 5′-nucleotidase (5′-ribonucleotide phosphohydrolase, EC 3.1.3.5) in T lymphoblasts may explain the marked sensitivity of this cell to deoxynucleotide accumulation when compared to B lymphoblasts. The relevance of such observations with cultured cells to the normal immune system requires the demonstration of similar differences in the 5′-nucleotidase activity of normal human lymphocyte subpopulations. Sheep erythrocyte (E) rosette-forming cells from normal thymus, tonsil, and peripheral mononuclear cells have 5′-nucleotidase activities of 1.7, 11.3, and 21.2 nmol/hr per 106cells. Non-E-rosette forming cells from the peripheral blood or tonsil have 5′-nucleotidase activity comparable to the higher levels found in the peripheral E-RFC. Increased levels of 5′-nucleotidase activity may be a marker for post-thymic T lymphocytes. T lymphoblasts have 5′-nucleotidase activity similar to values demonstrated for E-RFC in thymus, whereas cultured B lymphoblasts have 5′-nucleotidase activity 15 times greater than that of T lymphoblasts. On the basis of these observations, the 5′-nucleotidase deficiency in congenital agammaglobulinemia has been reevaluated. In these patients the data indicate that peripheral E-rosette forming cells have the enzyme deficiency, demonstrating an abnormality of T lymphocytes in this disorder of immunoglobulin production.