Background: COPD patients may display eosinophilia, a disease feature targeted in several clinical drug programs. Although several mechanisms for B cell-eosinophil (eos) interactions have been suggested, their relationship in COPD lungs has remained poorly studied.

Aims: To investigate the relationship between tissue eos and B cells in COPD-affected distal lung tissues.

Methods: Surgical lung tissue was collected from 39 COPD patients (GOLD I-IV) and 15 non-COPD controls. Tissue eos and B-cells were identified by immunohistochemical (IHC) staining for ECP and CD20, respectively. A subset of the samples was subjected to single cell B cell profiling by multiplex IHC and subsequent histology-based single cell analysis. Analysed lung compartments included alveolar tissue, small airways, pulmonary blood vessels, and ectopic lymphoid tissues.

Results: Median total tissue eos increased in COPD (p<0.0001). COPD lungs also showed increased total tissue CD20⁺ B-cells (p=0.0005). Eos and B cell densities were statistically correlated, both within the whole study material (p<0.0001) and COPD patients alone (p<0.003). The B cell profiling revealed complex and microenvironmentally-dictated patterns of B cell subsets differentially expressing CD19, CD20, CD27, and CD38. Based on expression profiles, B cells could be identified as naive activated, memory cells, plasmablasts, memory switch activated etc.

Conclusion: Tissue eosinophilia is common in COPD and correlates with tissue infiltration of phenotypically diverse B cell populations. This observation supports the proposed link between eosinophilia and adaptive immunity in COPD and highlights the need for further research into the B cell ? eos crosstalk in COPD lungs.