Deficient natural killer (NK) cells in paroxysmal nocturnal haemoglobinuria (PNH): studies of lymphoid cells fractionated by discontinuous density gradient centrifugation.

Non-adherent, non-B lymphoid cells from six patients with PNH and six healthy subjects were fractionated by Percoll discontinuous density gradient centrifugation (DDGC). The cell distribution pattern, NK cell activity (NKA), large granular lymphocytes (LGL) count and surface marker phenotypes were studied. The distribution patterns of patients' cells did not significantly differ from the controls. The peak of the NKA was found in low density fractions where the maximum counts of LGL, Leu-7+2- cells and Leu-11+ cells were present. The NKA and the proportion of Leu-7+2- cells and Leu-11+ cells were significantly lower in patients with PNH (P less than 0.001 for NKA and surface phenotypes; P less than 0.02 for LGL counts). NKA in the Percoll fractions was correlated with the counts of LGL (r=0.69, P less than 0.001), Leu-7+2- cells (r = 0.75, P less than 0.001) and Leu-11+ cells (r = 0.89, P less than 0.001). Therefore, we concluded that NKA is deficient in PNH because of decreased NK cell counts.