Impaired natural killer cell activity in patients with inflammatory bowel disease: evidence for a qualitative defect.

The natural killer cell lymphocyte may represent an important element in immune defense. Since host defense may be abnormal in patients with inflammatory bowel disease, we assessed natural killer cell function in 34 patients with ulcerative colitis and Crohn's disease. Lymphocytes from 31 of 34 patients (91%) exhibited decreased natural killer cell activity (mean cytotoxicity +/- SEM was 25% +/- 7.5% of the mean normal values, p less than 0.01). Disease activity, type of disease, and steroid therapy had no influence on these values. None of the 10 age-matched disease controls with other intestinal inflammatory conditions had natural killer cell activity outside the normal range. The numbers of circulating killer cells present in patients with impaired activity were quantified using a cytofluorometric detection system. All patients tested had normal numbers of cells binding nonaggregated immunoglobulin G (Fc receptor positive) despite decreased natural killer cell activity. It appears that by using this cytofluorometric detection technique, decreased natural killer cell activity is not the consequence of diminished numbers of natural killer cells.