Interleukin-18 overproduction exacerbates the development of colitis with markedly infiltrated macrophages in interleukin-18 transgenic mice

Background and Aim: The authors have previously shown that production of interleukin (IL)-18 was increased in the inflamed mucosa of patients with Crohn's disease (CD) and blockade of IL-18 ameliorated the murine model of CD. This demonstrated that IL-18 plays a significant role during intestinal inflammation. However, the initial role of IL-18 during intestinal inflammation was unclear; therefore the susceptibility of IL-18 transgenic (Tg) mice to acute dextran sulfate sodium (DSS)-induced colitis was examined. Methods: Interleukin-18 Tg and wild-type (WT) mice were fed 2.0% of DSS for 8 days. The total clinical scores (bodyweight loss, stool consistency, and rectal bleeding), colon length and histological scores were assessed. The expressions of surface markers and IL-18 on infiltrating lamina propria mononuclear cells were analyzed immunohistochemistrically. Mesenteric lymph node (MLN) cells were isolated and the expressions of CD4⁺ T-cell activation markers (CD69, CD25 and IL18R) were analyzed by flow cytometry. Results: The IL-18 Tg mice exhibited an increased susceptibility to DSS-induced colitis, as shown by significantly increased clinical, histological scores, and more severe colonic shortening compared with WT mice. Immunohistochemical analysis revealed a significant increase of IL-18 production and CD11b⁺ macrophages but not CD4⁺T cells in the inflamed mucosa in DSS-fed IL-18 Tg compared with DSS-fed WT mice. Furthermore, MLN cells revealed no evidence of increased CD4⁺T-cell activation in DSS-fed IL-18 Tg. Conclusions: These findings suggest that IL-18 overproduction in the mucosa plays an important role in the marked infiltration of macrophages and exacerbates colitis in IL-18 Tg mice.