Natural killer lymphocytes in hairy cell leukemia: presence of phenotypically identifiable cells with defective functional activity.

Eleven patients with hairy cell leukemia (HCL) were studied to determine the number and function of circulating natural killer (NK) lymphocytes in this disorder using a well-defined surface marker of these cells (Mac-1), the fluorescence-activated cell sorter (FACS), and a standard 51Cr release assay to determine cytotoxicity against the K562 cell line. Four of these patients demonstrated normal numbers of phenotypic and morphological (large granular lymphocyte) NK cells in the blood, but these cells showed a severe functional deficiency in their ability to lyse the K562 target. Sorting experiments demonstrated that although all of the NK activity was contained within the phenotypically identifiable NK population, the defect in NK function persisted even when these cells were isolated from other cell populations. Of the remaining seven patients, two had normal numbers and function of NK cells and five showed a marked deficiency of both phenotypic NK cells in the blood and NK function. These data suggest that the marked in vitro functional deficiencies of NK activity that occur in a majority of patients with HCL are sometimes associated with the preservation of phenotypically identifiable NK cells that are qualitatively rather than quantitatively deficient.