Objective: To investigate the expression of interleukin 18 (IL-18) in intestinal mucosa of patients with inflammatory bowel disease (IBD) and its relation with disease active state.

Methods: IL-18mRNA transcripts were evaluated by using a semiquantitative RT-PCR protocol. Specimens of 23 Crohn's disease (CD) and 20 ulcerative colitis (UC) patients and 20 controls were studied by immunohistochemical staining.

Results: Transcripts of IL-18 were found to be increased significantly in intestinal mucosa from active CD compared with UC and control. Immunohistochemical staining analysis localized the expression of IL-18 to intestinal epithelial cells and lamina propria (macrophages and dendritic cells, mainly). Staining was more intense in active CD compared with UC and control. Both transcriptions and staining of IL-18 in active UC were elevated, but there was no significant difference compared with control. Expression of IL-18 decreased in inactive CD (n = 9) or UC (n = 11) compared with active state of the same patients, and the difference in CD had significance.

Conclusions: IL-18 may be involved in the pathogenesis of IBD and related with CD activity.