The Role of the Environment in Eosinophilic Esophagitis.

Eosinophilic esophagitis (EoE) is a chronic, immune-mediated inflammatory disease with incompletely understood pathogenesis. Though disease manifestations were initially ascribed to a delayed reaction to food allergens, emerging evidence suggests that modifiable host factors and environmental allergen exposure may also play critical roles in the pathogenesis and ongoing manifestations of EoE. As with other atopic diseases, lack of early-life exposure to microbial pathogens leads to an immune tolerance defect and reprograms the commensal gut microflora toward a type 2 T helper (Th2) phenotype; the esophageal microbiota, a rich environment consisting of diverse bacterial species, is greatly altered by inflammation. Although multiple early life microbiome-altering factors are associated with EoE development, no causative, direct relationships have been identified. Interestingly, large, cross-sectional analyses of several populations identify an inverse relationship between Helicobacter pylori presence and EoE, likely via virulence factors that downregulate Th2 inflammation, though causality has not been proven. In regard to environmental allergens, some studies support seasonal variation in EoE diagnosis and flares, and EoE can be generated after a large, identifiable aeroallergen exposure. Examples include mouse models of intranasal Aspergillus dosing and following initiation of oral immunotherapy to foods or environmental allergens. Conversely, treatment of allergic rhinoconjunctivitis may improve EoE symptoms, though data is limited to case reports and small series. Unfortunately, biologic therapies for atopic conditions have failed to improve EoE symptoms despite improvement in esophageal eosinophil count, though dupilumab shows promise in ongoing studies. Overall, this chapter shows that EoE pathogenesis is likely multifactorial, and the environment is a key component in our understanding of EoE.