Cytokines mediating the induction of chronic colitis and colitis-associated fibrosis

Abstract

To investigate the immunopathogenesis of inflammation-associated fibrosis we analyzed the chronic colitis and late-developing fibrosis occurring in BALB/c mice administered weekly doses of intrarectal trinitrobenzene sulfonic acid (TNBS). We showed first in this model that an initial T helper type 1 response involving interleukin (IL)-12p70 and interferon-gamma subsides after 3 weeks to be supplanted by an IL-23/IL-25 response beginning after 4-5 weeks. This evolution is followed by gradually increasing production of IL-17 and cytokines ordinarily seen in a T helper type 2 response, particularly IL-13, which reaches a plateau at 8-9 weeks. We then show that IL-13 production results in the induction of an IL-13 receptor formerly thought to function only as a decoy receptor, IL-13Ralpha(2), and this receptor is critical to the production of tumor growth factor (TGF)-beta(1) and the onset of fibrosis. Thus, if IL-13 signaling through this receptor is blocked by administration of soluble IL-13Ralpha(2)-Fc, or by administration of IL-13Ralpha(2)-specific siRNA, TGF-beta(1) is not produced and fibrosis does not occur. These studies show that in chronic TNBS colitis, fibrosis is dependent on the development of an IL-13 response that acts through a novel cell-surface-expressed IL-13 receptor to induce TGF-beta(1).

Figure 1

Collagen content of the colon. Collagen content was determined during chronic TNBS-colitis and chronic Ethanol administration by a Sircol assay. Data shown are mean values ± SD and are derived from at least five mice per group; **, p < 0.01.

Figure 2

Cytokine production of colonic lamina propria mononuclear cells at weekly time points during chronic TNBS-colitis in BALB/c mice. Lamina propria mononuclear cells were extracted from the lamina propria and cultured for 48h in the presence of T cell or APC stimulants. Cytokine concentrations in the culture supernatants were determined by cytokine-specific ELISA. Data shown represent an overview of the cytokine production during the time course of the animal model.

Figure 3

IL-13Rα₁ and IL-13Rα₂ expression in BALB/c mice during the course of chronic TNBS-colitis. IL-13Rα₁ expression is constitutive whereas IL-13Rα₂ expression is induced on day 35 during chronic TNBS-colitis. IL-13Rα₁ mRNA expression was determined by RT-PCR of RNA extracted from colonic LPMC and IL-13Rα₂ protein expression was determined by Western blot analysis analyzed of colonic LPMC lysates.

Figure 4

IL-13Rα₁ and IL-13Rα₂ expression after administration of pCI-sIL-13Rα₂-Fc, IL-13Rα₂-specific siRNA, or anti-TGF-β₁-antibody. IL-13Rα₂ expression (but not IL-13Rα₁) is reduced after treatment of mice with chronic TNBS-colitis with pCI-sIL-13Rα₂-Fc and IL-13Rα₂-specific siRNA. IL-13Rα₁ mRNA expression was determined by RT-PCR of RNA extracted from colonic LPMC and IL-13Rα₂ protein expression was determined by Western blot analysis analyzed of colonic LPMC lysates.

Figure 5

Collagen content of the colon after administration of pCI-sIL-13Rα₂-Fc, IL-13Rα₂-specific siRNA, or anti-TGF-β₁-antibody. Collagen content was determined during chronic TNBS-colitis by a Sircol assay. Data shown are mean values ± SD and are derived from at least five mice per group; **, p < 0.01.