Role of CD44⁺CCR2⁺CD64^-monocyte-derived macrophage in chronic rhinosinusitis with nasal polyps

Heterogeneity of monocyte-derived macrophages (MDMs) is gradually recognized in polyp tissue of chronic rhinosinusitis with nasal polyps (CRSwNP). However, the contributions of MDM subsets for sustaining inflammation remain unclear. This study therefore aimed to characterize MDM subsets in polyp tissues and estimate their functions. We identified MDM subsets in polyp tissues by flow cytometry, and analyzed the correlation between the expression of these subsets and disease severity. We also explored the similarities and differences between tissue MDMs and classical ex vivo polarized MDMs. By using appropriate substitutes for tissue MDMs, we investigated the function of MDMs. MDM1 (lin^-CD44⁺CD64⁺) and MDM3 (lin^-CD44⁺CCR2⁺CD64^-) were identified in polyp tissues by flow cytometry. Recurrent CRSwNP patients exhibited higher levels of MDM3 compared to non-recurrent patients. This increase in MDM3 was positively correlated with the Lund-Mackay score, the number of infiltrated tissue eosinophils, and IL-5 expression levels. Ex vivo polarized alternatively activated (M2a) macrophage preferentially expressed MDM3 marker genes, which can be used as the substitute for MDM3 within the polyp tissues. M2a macrophages engulfed more Staphylococcus aureus than classically activated (M1) macrophages. However, interferon lambda 1 (IFN-λ1) did not alter the bacterial killing efficiency of M2a macrophages, nor did it affect the activation of reactive oxidase substrate (ROS) and signal transducer and activator of transcription 1 (STAT1) pathway and viability. The increase in MDM3 within polyp tissues, similar to classical M2a macrophages, acted as bacterial reservoirs and contributed to persistent inflammation, offering insights into the underlying mechanisms of CRSwNP.