Distribution of 5'-nucleotidase in human lymphoid tissues.

Abstract

Low activity of 5''-nucleotidase (5''-ribonucleotide phosphohydrolase, EC 3.1.3.5) in T [thymus-derived] lymphoblasts may explain the marked sensitivity of this cell to deoxynucleotide accumulation when compared to B [bone marrow-derived] lymphoblasts. The relevance of such observations with cultured cells to the normal immune system required 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 had 5''-nucleotidase activities of 1.7, 11.3 and 21.2 nmol/h per 106 cells. Non-E-rosette forming cells from the peripheral blood or tonsil had 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 had 5''-nucleotidase activity similar to values demonstrated for E-RFC in thymus, whereas cultured B lymphoblasts had 5''-nucleotidase activity 15 times greater than T lymphoblasts. On the basis of these observations, the 5''-nucleotidase deficiency in congenital agammaglobulinemia was reevaluated. In these patients peripheral E-rosette forming cells apparently have the enzyme deficiency, demonstrating an abnormality of T lymphocytes in this disorder of immunoglobulin production.