Eosinophils, basophils, and type 2 immune microenvironments in COPD-affected lung tissue

Although elevated blood or sputum eosinophils are present in many patients with chronic obstructive pulmonary disease (COPD), uncertainties remain regarding the anatomical distribution pattern of lung-infiltrating eosinophils. Basophils have remained virtually unexplored in COPD. This study mapped tissue-infiltrating eosinophils, basophils, and eosinophil-promoting immune mechanisms in COPD-affected lungs. Surgical lung tissue and biopsies from major anatomical compartments were obtained from COPD patients with severity grades GOLD I-IV; never-smokers/smokers served as controls. Automated immunohistochemistry and in-situ hybridization identified immune cells, the type 2 immunity marker GATA3, and eotaxins (CCL11, CCL24). Eosinophils and basophils were present in all anatomical compartments of COPD-affected lungs and increased significantly in very severe COPD. The eosinophilia was strikingly patchy, and focal eosinophil-rich microenvironments were spatially linked with GATA3⁺ cells, including Th₂ lymphocytes and type 2 innate lymphoid cells. A similarly localised and IL-33/ST2-dependent eosinophilia was demonstrated in influenza-infected mice. Both mice and patients displayed spatially confined eotaxin signatures with CCL11⁺ fibroblasts and CCL24⁺ macrophages. In addition to identifying tissue basophilia as a novel feature of advanced COPD, the identification of spatially confined eosinophil-rich type 2 microenvironments represents a novel type of heterogeneity in the immunopathology of COPD that will likely have implications for personalised treatment.