Resident eosinophils in patients with chronic obstructive pulmonary disease: a pilot study

Eosinophilic inflammation is involved in approximately 20% of patients with chronic obstructive pulmonary disease (COPD). Research examining the role of eosinophils in the initiation and progression of COPD has yielded varying conclusions, potentially attributable to the different subtypes of eosinophils.

In this prospective observational study from Jan 2025 and Jun 2025, we included 27 patients with stable COPD and 10 controls. Blood samples were collected for eosinophil isolation, and flow-cytometry analysis was used to determine the subtype of eosinophil: resident eosinophils (rEos: Siglec-8⁺CD62L⁺IL-3R^low) or inflammatory eosinophils (iEos: Siglec-8⁺CD62L^lowIL-3R^hi). We also recorded and analyzed baseline characteristics, pulmonary function test results, and several cytokines.

The absolute number and proportion of rEos was significantly lower in patients with stable COPD compared to healthy controls. The absolute number of rEos (cell/uL) serves as a biomarker for predicting COPD (AUC 0.856; 95% CI 0.736-0.975). A ratio below 1.955 (odds ratio 0.231; 95% CI 0.063-0.841; p = 0.026) may be linked to COPD pathophysiology.

rEos levels were notably lower in stable COPD patients compared to healthy individuals and were associated with COPD presence. Future research should include larger, diverse groups in multicenter studies to confirm the role of rEos in COPD and conduct basic experiments to investigate the molecular and cellular pathways of eosinophilic phenotypes in COPD patients.