Natural killer cell activity in patients with inflammatory bowel disease.

It has been suggested that the "natural killer" (NK) cell may play an important role in immune surveillance against tumors and viral-infected cells. With the use of 51Cr-labeled K-562 as target cells, we assessed natural killer cell activity in patients with inflammatory bowel disease (IBD). In ulcerative colitis (UC) patients' NK cell activity in the remissive and active stages was not significantly different with normal controls. In Crohn's disease (CD) patients' NK cell activity was significantly below normal levels in both remissive and active stages. Furthermore, in the active stage NK cell activity was significantly lower than that in the remissive stage in CD patients. Using the anti-Leu-11a monoclonal antibody, we quantified the number of circulating NK cells in CD patients. Decreased NK activity in CD patients is most likely not the consequence of diminished numbers of NK cells or of maturational defects of NK precursor cells. Macrophage seems to be one of the factors related to decreased NK cell activity. Further, impairment of NK cell activity in CD patients is reversible. It is possible that NK cell activity in CD patients recovers to the normal level.