A Phenotypically Distinct Subset of Eosinophils is Recovered with Intestinal Intraepithelial Leukocytes

In health, intestinal eosinophils contribute to mucosal immunity. In disease, eosinophils are associated with GI disorders such as food allergies and eosinophilic gastrointestinal diseases (EGIDs). However, the phenotype and functions of intestinal eosinophils in health or disease are poorly understood. This study assessed the phenotype, in situ localization, and capacity for in vivo antigen acquisition of intestinal eosinophils from naïve and allergic mice. Eosinophils were isolated from intestinal lamina propria (LP) and intraepithelial (IE) leukocyte populations, and their surface phenotypes were assessed by flow cytometry. In situ localization of intestinal eosinophils was assessed by fluorescence microscopy from tissue sections from mice expressing eosinophil-targeted GFP. In vivo uptake of lumen-derived antigen in live mice was accomplished using an intestinal loop surgical model. Compared to blood eosinophils, LP eosinophils had increased surface expressions of CD11b, CD11c, MHC II and CD80. A subset of eosinophils was also detected within IE preparations from naïve and allergen-challenged mice. IE eosinophils were phenotypically distinguished from LP eosinophils by increased expressions of Siglec F, CD11b and CD11c, and with low to no detectable surface MHC II. Both LP and IE eosinophil populations from allergen-sensitized mice acquired fluorescently-labeled soluble antigens deposited directly into the intestinal lumen within 45 minutes of allergen delivery. These findings identify a novel subset of tissue-dwelling eosinophils present at baseline within the intestinal IE niche and provide phenotypic insights into the unique preparedness of resident intestinal eosinophils to engage in antigen-specific functions in vivo.