Significance of Interleukin (IL)-15 in IgE associated eosinophilic Esophagitis (EoE).

Background and aim: IgE-mediated immune responses contribute to the pathogenesis of eosinophilic esophagitis (EoE). Interleukin (IL)-4 is a well-established cytokine involved in B cell activation, immunoglobulin (Ig) E production and isotype class switching. Earlier reports indicated that IL-15, B cells and IgE are induced in EoE pathogenesis. Therefore, we hypothesized that induced IL-15 and IgE may have a significant correlation in promoting EoE pathogenesis.

Methods: Accordingly, we performed ELISA, qPCR, flowcytometric and immunostaining analyses to examine IgE, B cells, eosinophils and mast cells in the esophagus of IL-15 overexpressed mice following EoE induction.

Results: Herein, we show that IL-15 overexpressed mice indeed have induced baseline IL-4, B cells, eosinophils, mast cells and IgE levels in the blood and esophagus. Further, we observed that IL-15 overexpressed mice show induction of IgE, and accumulation of degranulated eosinophils and mast cells in allergen-induced experimental EoE. Notably, despite induced blood IgE, esophageal eosinophilia is not induced in intestinal fatty acid binding protein IL-15 overexpressed gene (Fabpi-IL-15) mice. Fabpi-IL-15 transgenic mice showed IgE in the blood and intestine and intestinal eosinophilia, but no esophageal eosinophilia at baseline and comparable eosinophils in the esophagus of saline and allergen challenged Fabpi-IL-15 mice. Similarly, allergen challenged IL-15 gene-deficient mice show reduced IgE and esophageal eosinophilia in allergen-induced experimental EoE.

Conclusions: Taken together, we for the first time provide direct evidence that tissue-specific IL-15 induced IgE mediated responses, not systemic IgE is critical in promoting EoE pathogenesis.