5' nucleotidase activity in leukaemic lymphocytes.

The enzyme 5' nucleotidase (E.C.3.1.3.5.) is present in lymphocytes isolated from the blood of normal subjects. The activity was extremely low in lymphocytes from 17 patients with B lymphocytic leukaemias. Removal of normal lymphocytes from the B-cell leukaemic samples decreased further the enzyme activity. Moderately low values were observed in three cases of T-ALL and in the cells from a case of Sézary syndrome. In contrast, normal or high values were observed in three cases of ALL in which T and B markers were not demonstrable and in two of T-CLL. No differences were observed in partially purified subpopulations of normal B and T cells.