Cutting Edge: IL-36 Receptor Promotes Resolution of Intestinal Damage

Abstract

IL-1 family members are central mediators of host defense. In this article, we show that the novel IL-1 family member IL-36γ was expressed during experimental colitis and human inflammatory bowel disease. Germ-free mice failed to induce IL-36γ in response to dextran sodium sulfate (DSS)-induced damage, suggesting that gut microbiota are involved in its induction. Surprisingly, IL-36R-deficient (Il1rl2(-/-)) mice exhibited defective recovery following DSS-induced damage and impaired closure of colonic mucosal biopsy wounds, which coincided with impaired neutrophil accumulation in the wound bed. Failure of Il1rl2(-/-) mice to recover from DSS-induced damage was associated with a profound reduction in IL-22 expression, particularly by colonic neutrophils. Defective recovery of Il1rl2(-/-) mice could be rescued by an aryl hydrocarbon receptor agonist, which was sufficient to restore IL-22 expression and promote full recovery from DSS-induced damage. These findings implicate the IL-36/IL-36R axis in the resolution of intestinal mucosal wounds.

FIGURE 1

IL-36γ is expressed during experimental colitis and human IBD. (A) IL-36γ, IL-36γ, and IL-36γ mRNA expression in colons of WT mice treated for 5 d with DSS. (B) ELISA and WB analyses of IL-36γ in colons of WT mice treated as in (A). (C) IL-36γ mRNA expression in colonic tissue from CTL, DSS (5 d), CD45RB^hi, and H. hepaticus models of colitis. (D) IL-36γ mRNA expression in CTL, IBD, UC, or CD human mucosa samples. (E) IL-36γ mRNA expression from cLP DC, Mϕ, IEL, and IEC from WT mice treated as in (A). (F) IL-36γ mRNA expression in colons of WT mice housed under CNV or GF conditions and treated as in (A). Data are representative of two or three independent experiments with four or five mice per group. *P < 0.05.

FIGURE 2

IL-36R contributes to colonic wound healing. (A) DAI of Il1rl2^+/+ and Il1rl2^−/− mice treated for 5 d with DSS followed by normal water for 8 d. (B) Image and length of Il1rl2^+/+ and Il1rl2^−/− colons from mice treated as in (A) at 13 d. (C) H&E staining and (D) histology scoring of colon sections from Il1rl2^+/+ and Il1rl2^−/− mice treated as in (A) at 13 d. (E) Endoscopic images at 2 d and 4 d and (F) Quantification at 4 d of wound repair in Il1rl2^+/+ and Il1rl2^−/− mice after biopsy-induced injury. Arrows indicate the wound bed. Data are representative of three independent experiments with five mice per group. *P < 0.05.

FIGURE 3

IL-36R contributes to DSS-induced IL-22 production. (A) Time course of IL-36γ and IL-22 mRNA expression in colons of WT mice treated for 5 d with DSS. (B) ELISA of IL-22 in colons of Il1rl2^+/+ and Il1rl2^−/− mice treated for 5 d or 8 d with DSS. (C) FACS plots and (D) absolute cell numbers of IL-22-producing colonic T cells, ILCs and Nϕ in the colon of Il1rl2^+/+ or Il1rl2^−/− mice treated as in (A). Data are representative of two or three independent experiments with four or five mice per group. *P < 0.05.

FIGURE 4

FICZ induces IL-22 and resolution of colonic damage in Il1rl2^−/− mice. (A) DAI of Il1rl2^+/+ (blue) and Il1rl2^−/− (red) mice treated for 5 d with DSS followed by normal water for 8 days, in the presence (black line) or absence (no line) of FICZ. (B) H&E staining and (C) histology scoring of colon sections of Il1rl2^+/+ and Il1rl2^−/− mice treated as in (A). (D) IL-22 mRNA expression in colons from DSS-treated Il1rl2^−/− mice in the presence or absence of FICZ (5 d). Data are representative of three independent experiments with five mice per group. *P < 0.05.