SUPPRESSED NATURAL-KILLER-CELL ACTIVITY IN PATIENTS WITH CHRONIC AUTOIMMUNE THROMBOCYTOPENIC PURPURA

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 chromium-51 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.