BACKGROUND Inflammatory bowel disease (IBD) is characterised by infiltration of inflamed mucosal regions with CD4⁺ T lymphocytes and other mononuclear cells. Interleukin (IL)-16 exerts a strong chemoattractant activity on CD4⁺ cells. Moreover, IL-16 activates expression and production of proinflammatory cytokines such as IL-1β, IL-6, IL-15, and tumour necrosis factor α (TNF-α) in human monocytes.

AIM To examine if IL-16 expression is increased in IBD patients compared with healthy controls.

RESULTS IL-16 mRNA and protein expression in the colonic mucosa of IBD patients were increased twofold compared with healthy controls, DSC, or IBD patients under steroid treatment. Most of the detected IL-16 protein was in its bioactive 17 kDa form and was predominantly expressed in eosinophils. Increased IL-16 expression in UC patients appeared to be mainly restricted to the inflamed regions of the colonic mucosa. Levels of caspase 3, which processes the 68 kDa IL-16 precursor molecule into the biological active 17 kDa form, were not increased.

CONCLUSIONS Our results provide evidence that IL-16 expression is significantly increased in the inflamed colonic mucosa of IBD patients but not in control individuals, DSC, or patients under steroid treatment. Therefore, upregulation of IL-16 expression seems to be specific for chronic intestinal inflammation and could lead to increased secretion of other proinflammatory cytokines in IBD.