Allergen-induced resistin-like molecule-α promotes esophageal epithelial cell hyperplasia in eosinophilic esophagitis

Resistin-like molecule (Relm)-α is a secreted, cysteine-rich protein belonging to a newly defined family of proteins, including resistin, Relm-β, and Relm-γ. Although resistin was initially defined based on its insulin-resistance activity, the family members are highly induced in various inflammatory states. Earlier studies implicated Relm-α in insulin resistance, asthmatic responses, and intestinal inflammation; however, its function still remains an enigma. We now report that Relm-α is strongly induced in the esophagus in an allergen-challenged murine model of eosinophilic esophagitis (EoE). Furthermore, to understand the in vivo role of Relm-α, we generated Relm-α gene-inducible bitransgenic mice by using lung-specific CC-10 promoter (CC10-rtTA-Relm-α). We found Relm-α protein is significantly induced in the esophagus of CC10-rtTA-Relm-α bitransgenic mice exposed to doxycycline food. The most prominent effect observed by the induction of Relm-α is epithelial cell hyperplasia, basal layer thickness, accumulation of activated CD4(+) and CD4(-) T cell subsets, and eosinophilic inflammation in the esophagus. The in vitro experiments further confirm that Relm-α promotes primary epithelial cell proliferation but has no chemotactic activity for eosinophils. Taken together, our studies report for the first time that Relm-α induction in the esophagus has a major role in promoting epithelial cell hyperplasia and basal layer thickness, and the accumulation of activated CD4(+) and CD4(-) T cell subsets may be responsible for partial esophageal eosinophilia in the mouse models of EoE. Notably, the epithelial cell hyperplasia and basal layer thickness are the characteristic features commonly observed in human EoE.

Pathogenic role of mast cells in experimental eosinophilic esophagitis

Eosinophilic esophagitis (EoE) is a chronic allergic disease characterized by esophageal intraepithelial eosinophils, extracellular eosinophil granule deposition, induced mast cell accumulation, and epithelial cell hyperplasia. However, the processes involved in the development of a number of these characteristics are largely unknown. Herein, we tested the hypothesis whether induced mast cell accumulation in the esophagus has a role in promoting EoE pathogenesis. Accordingly, we induced experimental EoE in wild-type mice, mast cell-deficient WWv mice, and mast cell-reconstituted WWv mice. We report that esophageal mast cell numbers increase in parallel with eosinophils in a dose- and time-dependent manner following the induction of allergen-induced EoE. The induced mast cells are localized in the esophageal lamina propria and muscular mucosa but have no influence on promoting esophageal eosinophilia. The 5'-bromodeoxyuridine (BrdU) incorporation analysis indicated that mast cells have a significant role in muscle cell hyperplasia and hypertrophy. In addition, the wild-type and mast cell-reconstituted WWv mice showed a comparable number of BrdU⁺ cells in the esophageal muscular mucosa following allergen-induced EoE. In conclusion, we provide for the first time direct evidence that mast cell promotes muscle cell hyperplasia and hypertrophy and may have a significant role in promoting esophageal functional abnormalities in EoE.

Esophageal functional impairments in experimental eosinophilic esophagitis

Eosinophilic esophagitis (EoE) is an emerging chronic esophageal disease. Despite the increasing diagnosis of EoE globally, the causes of EoE and other esophageal eosinophilic disorders are not clearly understood. EoE pathology includes accumulation of inflammatory cells (e.g., eosinophils, mast cells), characteristic endoscopic features (e.g., furrows, the formation of fine concentric mucosal rings, exudates), and functional impairments (e.g., esophageal stricture, dysmotility). We hypothesized that the esophageal structural pathology and functional impairments of EoE develop as a consequence of the effector functions of the accumulated inflammatory cells. We analyzed eosinophils (anti-major basic protein immunostaining), esophageal stricture (X-ray barium swallowing), and esophageal motility (isometric force) in two established transgenic murine models of EoE (CD2-IL-5 and rtTA-CC10-IL-13) and a novel eosinophil-deficient model (ΔdblGATA/CD2-IL-5). Herein, we show the following: 1) CD2-IL-5 and doxycycline (DOX)-induced rtTA-CC10-IL-13 mice have chronic eosinophilic and mast cell esophageal inflammation; 2) eosinophilic esophageal inflammation promotes esophageal stricture in both transgenic murine models; 3) the eosinophil-deficient ΔdblGATA/CD-2-IL-5 mice were protected from the induction of stricture, whereas the eosinophil-competent CD2-IL-5 mice develop esophageal stricture; 4) esophageal stricture is not reversible in DOX-induced rtTA-CC10-IL-13 mice (8 wk DOX followed by 8 wk no-DOX); and 5) IL-5 transgene-induced (CD2-IL-5) EoE evidences esophageal dysmotility (relaxation and contraction) that is independent of the eosinophilic esophageal inflammation: CD2-IL-5 and ΔdblGATA/CD2-IL-5 mice have comparable esophageal dysmotility. Collectively, our present study directly implicates chronic eosinophilic inflammation in the development of the esophageal structural impairments of experimental EoE.

Interleukin-15 expression is increased in human eosinophilic esophagitis and mediates pathogenesis in mice

BACKGROUND & AIMS

Quantitative microarray analyses have shown increased expression of interleukin-15 (IL-15) messenger RNA in the esophagus of patients with eosinophilic esophagitis (EoE), a recently recognized allergic disorder with poorly understood pathogenesis.

METHODS

Quantitative polymerase chain reaction and enzyme-linked immunosorbent assay analyses were performed to examine protein and transcript levels in tissue samples from patients with EoE. Tissues from IL-15Ra-deficient and wild-type (control) mice were also examined. Tissue eosinophilia was determined by immunostaining for major basic protein and flow cytometry for cell-surface receptors.

RESULTS

Quantitative polymerase chain reaction analyses showed that levels of IL-15 and its receptor IL-15Ra were increased approximately 6- and approximately 10-fold, respectively, in tissues from patients with EoE and approximately 3- and approximately 4-fold, respectively, in mice with allergen-induced EoE. A >2-fold increase in serum IL-15 protein levels was also detected in human EoE samples compared with those from healthy individuals. Human IL-15 messenger RNA levels correlated with esophageal eosinophilia (P < .001). IL-15Ra-deficient mice were protected from allergen-induced esophageal eosinophilia compared with controls (P < .001), even though similar levels of airway eosinophilia were observed in all mice. IL-15 activated STAT5 and CD4(+) T cells to produce cytokines that act on eosinophils. Incubation of primary esophageal epithelial cells from mice and humans with IL-15 caused a dose-dependent increase in the mRNA expression and protein levels of eotaxin-1, -2, and -3.

CONCLUSIONS

IL-15 mediates in the pathogenesis of EoE. IL-15 activates CD4(+) T cells to produce cytokines that act on eosinophils.

Indoor insect allergens are potent inducers of experimental eosinophilic esophagitis in mice

EE is an emerging disease reported in children and adults of urbanized countries, where indoor insect allergens are major health risk factors. Review of our hospital patient database uncovered that a number of EE patients have hypersensitivity to indoor cat, dog, cockroach, and dust mite allergens. We tested the hypothesis whether inhaled indoor insect allergens are effective inducers of experimental EE. We delivered cat, dog, cockroach, and dust mite allergen extracts intranasally to wild-type and eotaxin-1/2-, CCR3-, and IL-5-deficient mice. Interestingly, wild-type mice exposed to cockroach or dust mite allergens develop a significant increase in the levels of esophageal eosinophils and mast cells compared with saline-challenged mice. The eosinophil numbers in the esophagus of cockroach- and dust mite-exposed mice were 18.3+/-6.8/mm2 and 33.4+/-11.1/mm2 compared with 2.3+/-1.8/mm2 and 2.1+/-1.2/mm2 in saline-challenged mice. Additionally, we observed an additive effect of these two allergens in inducing esophageal eosinophilia and mastocytosis. Histopathological analysis detected intraepithelial esophageal eosinophilia in mice exposed to both allergens. Furthermore, mice exposed to cockroach and/or dust mite had increased levels of total IgE and antigen-specific IgG1 in the blood and increased esophageal expression of eosinophil-active cytokines (IL-13) and chemokines (eotaxin-1). Notably, mice deficient in eotaxin-1/2, CCR3, and IL-5 showed ablated esophageal eosinophilia following cockroach or dust mite allergen exposure. These data indicate that indoor insect allergens are potent inducers of IL-5 and eotaxin-mediated esophageal eosinophilia. These experimental studies are in accordance with clinical data but may have some limitations inherent to animal models of human disease.