Ultrastructural localization of 5'nucleotidase in human normal and malignant lymphoid cells

5'Nucleotidase (EC 3.1.3.5), a purine pathway enzyme, occurs as a cellular ectoenzyme. Widely differing 5'N activity has been reported in different types of lymphoid cells and appears to be related to lymphocyte function, differentiation and immunological subtype. This paper reports a study on the ultrastructural distribution of 5'N in in different types of lymphoid leukemias and non-Hodgkin's lymphomas. In lymphoid leukemias, only cALL cells showed strong 5'N staining. In CLL, PLL and HCL the intensity of staining was less than in normal cells. In the NHL group, the reaction pattern was mixed. Infiltrating neoplastic cells, specially the large lymphoid cells, consistently showed very mild activity of the enzyme, whereas follicular center cells and other mature lymphocytes were characterized by moderately strong to strong 5'N activity. These results support the view that 5'N is a marker of lymphocyte cell differentiation.