• natural killer cells;
  • autoimmunity;
  • thrombocytopenia


Natural killer (NK) cell activity was studied in 17 patients with primary chronic idiopathic autoimmune thrombocytopenic purpura (ATP). Fifteen of 17 patients had a significantly reduced NK cytotoxicity against 51chromium labeled K562 target cells (mean LU20% = 18 ± 20 in patients versus 65 = 2 5 in controls, P < 0.001). NK activity was also significantly reduced in all of six patients with secondary ATP as compared with normal controls (LU20%28±15, respectively, P < 0.005). The NK activity in both patient groups correlated with the duration of therapy being received (r = 0.60, P < 0.001). Immunophenotypic analysis of peripheral blood mononuclear cells from patients with ATP revealed that CD8- cells bearing CD57 (HNK-1, Leu 7) and CD3- cells bearing CD56 (Leu 19) were quantitatively within the normal range. These findings indicate that patients with ATP have a functional defect in NK cytolytic activity.