5' Nucleotidase in chronic B cell leukemias: a cytochemical and ultrastructural study

We studied by cytochemical means the distribution of 5' nucleotidase (5' NT), a purine degradative enzyme, in the circulating lymphocytes of 24 healthy donors and 41 cases of chronic lymphoid leukemias, classified according to morphological and immunological criteria. About half the normal circulating lymphocytes were 5'NT positive and exhibited variable degrees of enzyme activity. Among chronic B lymphocytic leukemias we found high percentages of positive cells only in the phenotypically more mature cases. Moreover all cases of hairy cell, follicular cell, lymphoplasmacytic, and plasma cell leukemia showed moderate or weak 5' NT reactivity. Also one case of chronic T lymphocytic leukemia, CD8 positive, was moderately positive, while another, with large granular lymphocyte morphology, was completely negative. Electron microscopy revealed a discontinuous, granular plasma membrane reaction pattern, varying in intensity from case to case. In conclusion, our results confirm the usefulness of the 5' NT cytochemical reaction for identification of lymphoid populations at different stages of maturation in chronic B cell disorders.