Objective: The presence of natural killer cells in the colon mucosa of patients with ulcerative colitis has not been studied, therefore, the study was designed to investigate the densities of cells expressing CD3+, CD4+, CD8+, CD56+ and the new CD94+ in colon mucosa of active and inactive ulcerative colitis patients.

Methods: Twenty ulcerative colitis patients, 10 with active disease and 10 with inactive disease, and 10 subjects with a histologically normal rectal mucosa were used as patients and controls. Additionally, a subgroup of 6 patients with active proctitis has been studied. Two biopsy specimens from rectal mucosa were taken for all patients and controls. Two biopsy specimens of proximal colon mucosa of the subgroup of 6 patients were also taken. One biopsy was processed for immunohistochemical studies and another for histologic study.

Results: The densities of CD3+, CD16+, CD56+ and CD 94+ were significantly increased in active ulcerative colitis patients compared to inactive subjects (P < 0.001). The increase in the CD4+ and CD8+ was not statistically significant. Patients with inactive ulcerative colitis also presented increased numbers of CD3+, CD56+ and CD94+ cells compared to controls (P < 0.001). In the subgroup of proctitis, the densities of cells expressing all the antigens were significantly lower in the normal mucosa compared to the affected colon (P < 0.001). No differences in the number of lamina propria DC1a+ cells between patients and controls were found.

Conclusions: These findings suggest that natural killer cells are increased in active ulcerative colitis subjects and that the affected mucosa of ulcerative colitis patients with inactive disease is in state of "latent" inflammation. On the other hand, the normal looking mucosa from active ulcerative colitis patients does not differ from the mucosa of control subjects. Therefore, it seems that in ulcerative colitis the immunological alterations are limited to the affected mucosa.