Distinct roles for IL-13 and IL-4 via IL-13 receptor alpha1 and the type II IL-4 receptor in asthma pathogenesis

Abstract

IL-13 and IL-4 are central T helper 2 (Th2) cytokines in the immune system and potent activators of inflammatory responses and fibrosis during Th2 inflammation. Recent studies using Il13ra1(-/-) mice have demonstrated a critical role for IL-13 receptor (IL-13R) alpha1 in allergen-induced airway responses. However, these observations require further attention especially because IL-4 can induce similar lung pathology to IL-13, independent of IL-13, and is still present in the allergic lung. Thus, we hypothesized that IL-13Ralpha1 regulates IL-4-induced responses in the lung. To dissect the role of IL-13Ralpha1 and the type I and II IL-4Rs in experimental asthma, we examined lung pathology induced by allergen, IL-4, and IL-13 challenge in Il13ra1(-/-) mice. We report that IL-13Ralpha1 is essential for baseline IgE production, but Th2 and IgE responses to T cell-dependent antigens are IL-13Ralpha1-independent. Furthermore, we demonstrate that increased airway resistance, mucus, TGF-beta, and eotaxin(s) production, but not cellular infiltration, are critically dependent on IL-13Ralpha1. Surprisingly, our results identify a CCR3- and IL-13Ralpha1-independent pathway for lung eosinophilia. Global expression profiling of lungs from mice stimulated with allergen or IL-4 demonstrated that marker genes of alternatively activated macrophages are differentially regulated by the type I and type II IL-4R. Taken together, our data provide a comprehensive mechanistic analysis of the critical role by which IL-13Ralpha1 mediates allergic lung pathology and highlight unforeseen roles for the type II IL-4R.

Fig. 1.

Assessment of baseline serum IL-13Rα2 and IgE. (A and B) Assessment of total sIL-13Rα2 (free and bound to IL-13) and IL-13/sIL-13Rα2 complexes. The y axes in are shown in pg/ml where each dot represents a different mouse (n = 10 mice per group). ***, P < 0.001. (C) A graphic representation of the saturation status of sIL-13Rα2. (D and E) Total serum Ig concentrations were determined. ***, P < 0.01. IL-4, IFN-γ (F, day 5) and serum IgE levels (G) were monitored after goat anti-mouse IgD antiserum (GαM-IgD) injection. n = 2 (six mice per experimental group).

Fig. 2.

Assessment of IL-13Rα1-mediated responses in a model of IL-13-induced airway inflammation. Forty-eight hours after the final IL-13 challenge, the mice were assessed for BALF chemokine (A–D) and active TGF-β (E) levels, mucus production (F and G), airway resistance (H), and BALF cellular infiltration (I). Data are representative of three experiments (six to eight mice per experimental group). *, P < 0.05; **, P < 0.01; ***, P < 0.001.

Fig. 3.

Assessment of IL-13Rα1-mediated responses in allergen-induced airway inflammation. Twenty-four hours after the final allergen challenge, the mice were examined for BALF chemokine (A–D) and cytokine (E–H) production, active TGF-β production (I), mucus production (J and K), airway resistance (L), lung compliance (M), and BALF and lung cellular infiltration (N and O). Data are representative of one of three experiments (6–17 mice per experimental group). ns, not significant. *, P < 0.05; **, P < 0.01; ***, P < 0.001. Chemotaxis was assessed with eosinophils in response to BALF from allergen-challenged WT or Il13ra^−/− mice (P). “Isotype” indicates isotype-matched control, and “aCCR3” indicates anti-CCR3. Data are representative of three experiments. *, P < 0.05; **, P < 0.01; ***, P < 0.001.

Fig. 4.

Assessment of IL-13Rα1-mediated responses in a model of IL-4-induced airway inflammation. Twenty-four hours after the final IL-4C challenge the mice were assessed for mucus production (A and B), airway resistance (C), BALF cellular infiltration (D), and chemokine production (E–H). The data, representative of one of two experiments, are presented as mean ± SD (nine mice per experimental group). *, P < 0.05; ***, P < 0.001.

Fig. 5.

Identification of IL-13Rα1-dependent genes. DNA microarray analysis of allergen-challenged lungs from Il13ra1^−/− or WT mice identifies 33 altered genes (shown in parentheses) at baseline in the Il13ra1^−/− mice, 1,049 altered genes in the allergen-challenged WT mice, and 608 altered genes in the allergen-challenged Il13ra1^−/− mice (in comparison with saline-treated mice) (A). Comparison of microarray data obtained from the lungs of allergen-challenged mice reveals a subset of 205 altered genes that are depicted in four clusters as shown (B). Several allergen-induced IL-13Rα1-dependent genes are shown (C). Comparison of microarray data obtained from IL-4-challenged mice reveals a subset of 63 altered genes that are dysregulated (D). Several IL-4-induced IL-13Rα1-dependent genes are depicted (E).