Intestinal eosinophils are implicated in homeostatic and disease-associated processes, yet the phenotype of intestinal tissue-dwelling eosinophils is poorly defined and their roles in intestinal health or disease remain enigmatic. Here we probed the phenotype and localization of eosinophils constitutively homed to the small intestine of naive mice at baseline, and of antigen-sensitized mice following intestinal challenge. Eosinophils homed to the intestinal lamina propria of naive mice were phenotypically distinguished from autologous blood eosinophils, and constitutively expressed antigen-presenting cell markers, suggesting that intestinal eosinophils, unlike blood eosinophils, may be primed for antigen presentation. We further identified a previously unrecognized resident population of CD11c eosinophils that are recovered with intraepithelial leucocytes, and that are phenotypically distinct from both lamina propria and blood eosinophils. To better visualize intestinal eosinophils in situ, we generated eosinophil reporter mice wherein green fluorescent protein expression is targeted to both granule-delimiting and plasma membranes. Analyses of deconvolved fluorescent z-section image stacks of intestinal tissue sections from eosinophil reporter mice revealed eosinophils within intestinal villi exhibited dendritic morphologies with cellular extensions that often contacted the basement membrane. Using an in vivo model of antigen acquisition in antigen-sensitized mice, we demonstrate that both lamina propria-associated and intraepithelium-associated eosinophils encounter, and are competent to acquire, lumen-derived antigen. Taken together these data provide new foundational insights into the organization and functional potential of intestinal tissue-dwelling eosinophils, including the recognition of different subsets of resident intestinal eosinophils, and constitutive expression of antigen-presenting cell markers.

The natural history of allergic diseases suggests bidirectional and progressive relationships between allergic disorders of the skin, lung and gut indicative of mucosal organ cross-talk. However, impacts of local allergic inflammation on the cellular landscape of remote mucosal organs along the skin:lung:gut axis are not yet known. Eosinophils are tissue-dwelling innate immune leukocytes associated with allergic diseases. Emerging data suggest heterogeneous phenotypes of tissue-dwelling eosinophils contribute to multifaceted roles that favor homeostasis or disease. This study investigated the impact of acute local allergen exposure on the frequency and phenotype of tissue eosinophils within remote mucosal organs. Our findings demonstrate allergen challenge to skin, lung or gut elicited not only local eosinophilic inflammation, but also increased the number and frequency of eosinophils within remote, allergen non -exposed lung and intestine. Remote allergen-elicited lung eosinophils exhibited an inflammatory phenotype and their presence associated with enhanced susceptibility to airway inflammation induced upon subsequent inhalation of a different allergen. These data demonstrate, for the first time, a direct effect of acute allergic inflammation on the phenotype and frequency of tissue eosinophils within antigen non-exposed remote mucosal tissues associated with remote organ priming for allergic inflammation.