Although eosinophils are the cardinal cellular feature defining EGIDs, how they participate in EGID pathophysiology is not understood. Our active ongoing studies are working toward: 1) Discriminating putatively “helpful” from “harmful” eosinophil subsets in EGID patient biopsies; 2) Elucidating functions of tissue eosinophils that drive pathology or promote tissue healing in EGIDs; and 3) Delineating the biological relevance of IgG4 deposition from local tissue plasma cells.