Decreased frequency of bone marrow NK progenitors in aplastic anaemia.

Twelve patients with aplastic anaemia were studied with regard to the frequency of NK progenitors in the bone marrow (BM) to investigate the mechanism of depressed NK activity and low NK cell count in the peripheral blood. NK cell (CD16+ cell) count and NK (K562) activity were significantly decreased (P less than 0.02 and P less than 0.001, respectively) in the patients as compared to eight healthy control subjects. Nylon wool non-adherent (NW-NA) BM mononuclear cells (MNC) of each patient and control were prepared. Mature T and NK cells were extensively depleted by sheep red cell rosette formation followed by a centrifugation on Ficoll-Hypaque and monoclonal antibody mediated complement dependent cytolysis. Those selected BM cells were cultured in the presence of recombinant interleukin 2 (rIL2). Generation of NK activity was significantly decreased (P less than 0.01) in the patients with aplastic anaemia. Frequency of NK progenitors in the selected BM cells assayed by the limiting dilution method was significantly decreased in those patients (P less than 0.05). The frequency of BM NK progenitors relative to NW-NA BM cells were related to NK cell count (P less than 0.01). Those results indicate that depressed NK activity in aplastic anaemia is closely related to decreased NK cell count which is probably due to decreased production of NK cells in the BM.