Allergen-induced interleukin-18 promotes experimental eosinophilic oesophagitis in mice.

Elevated levels of interleukin (IL)-18 have been reported in a number of allergic diseases. We recently reported that IL-18 in the blood and IL-18Rα mRNA in the oesophagus are induced during human eosinophilic oesophagitis (EoE). Additionally, we earlier showed that invariant natural killer T (iNKT) cells are critical to EoE pathogenesis; however, the mechanism of iNKT cell activation in EoE is not well understood. Therefore, the current study focused on the hypothesis that allergen-induced IL-18 may have an important role in iNKT cell-mediated EoE pathogenesis. We first validated the human EoE findings of IL-18 in experimental EoE by examining blood levels of IL-18 and oesophageal IL-18Rα mRNA levels in aeroallergen- and food allergen-induced experimental mouse models of EoE. We demonstrate that blood IL-18 protein and oesophageal IL-18Rα mRNA are induced in the mouse model of EoE and that IL-18Rα is expressed by iNKT cells in the oesophagus. Intranasal delivery of rIL-18 induced both mast cells and eosinophilic inflammation in the oesophagus in a time- and dose-dependent manner. To establish the significance of IL-18 in EoE pathogenesis, we examined DOX-inducible rtTA-CC10-IL-18 bitransgenic mice that induce IL-18 protein expression in the oesophagus. Our analysis indicated that induction of IL-18 in these mice resulted in the development of many of the characteristics of EoE, including oesophageal intraepithelial eosinophilia, increased mast cells, oesophageal remodelling and fibrosis. The current study provides evidence that IL-18 may induce iNKT cell activation to release the eosinophil-activating cytokine IL-5, as IL-5-deficient mice and iNKT cell-deficient (CD1d null) mice do not induce EoE in response to intranasal IL-18 challenge. Taken together, these findings provide evidence that allergen-induced IL-18 has a significant role in promoting IL-5- and iNKT-dependent EoE pathogenesis.

Involvement of interleukin-18 in the pathogenesis of human eosinophilic esophagitis.

IL-18 is induced in food allergy and EoE is food allergen-induced disease. Therefore, we tested the hypothesis whether IL-18 is involved in food allergen-induced EoE pathogenesis. Accordingly, we examined normal SPT+ and SPT- EoE patient blood and biopsy samples for IL-18, IL-18Rα, ICAM and VCAM expression. Herein, we show increased IL-18 level is highly significant in food allergen SPT+ compared to SPT- EoE patients. We also report that IL-18Rα+ cells and mRNA levels are induced in the esophageal biopsies of EoE patients and blood IL-18 levels correlate with esophageal eosinophilia (P<0.01). Additionally, we report that the levels of esophageal eosinophil and mast cells correlate with ICAM expression in human EoE. Mechanistically, we show that IL-18 in vitro stimulates iNKT cells and endothelial cells and induce eosinophil active cytokines IL-5 and IL-13. We provide the evidence that IL-18 is critical cytokine involved in activation of iNKT cells and ICAM in promoting human EoE.