Characterization of IL-6R-expressing monocytes in the lung of patients with chronic obstructive pulmonary disease [IL-6 mono]

Background: Monocytes play a crucial role in innate immune responses for host defense, yet their involvement in chronic obstructive pulmonary disease (COPD) remains poorly understood. We previously identified a subset of monocytes in COPD lung tissues characterized by high interleukin-6 receptor (IL-6R) expression. This study aimed to characterize the phenotypes of IL-6Rhi monocytes in the lung of COPD patients. Methods: Using flow cytometry, we assessed the abundance of pulmonary CD14+IL-6Rhi cells in never smokers (CNS), control ex-smokers (CES) and COPD patients. IL-6 expression in CD14+ monocytes from peripheral blood of patients with COPD was also examined. CD45+CD206–CD14+IL-6Rhi and CD45+CD206–CD14+IL-6R– cells were isolated from COPD lung tissues for transcriptome analysis. A monocyte line THP1 cell with constitutive IL-6R expression was stimulated with recombinant IL-6, followed by RNA sequencing to evaluate IL-6 responsiveness of IL-6R+ monocytes. Results: The number of pulmonary CD14+IL-6Rhi monocytes was elevated in COPD patients compared to CNS, while CD14+ monocytes in the peripheral blood of COPD patients did not express IL-6R. Upregulated mRNA expression in CD14+IL-6Rhi monocytes was associated with chemotaxis, monocyte differentiation, fatty acid metabolism and integrin-mediated signaling pathway. Stimulation of THP1 cells with recombinant IL-6 induced gene expression changes linked to chemotaxis and organism development. Conclusion: In patients with COPD, CD14+IL-6Rhi monocytes increase in lung tissues compared to CNS and exhibit a different transcriptome profile from CD14+IL-6R– monocytes.