Immunological studies on Crohn's disease. III. Defective natural killer activity.

Natural killer (NK) activity was studied in 23 patients with Crohn's disease (CD) and 23 healthy controls, as assessed by lymphocyte cytotoxicity against K562 target cells. Severely impaired NK activity was found in patients with CD (p less than 0.001). The relationship between NK activity and disease activity was also analyzed. NK activity was not directly related to the disease activity, although NK function was lower in the patients with an active form of the disease.