Chronic rhinosinusitis (CRS) is a chronic inflammatory disorder of nasal cavity and sinus, affecting about 10 % of the adult population throughout the world [1]. It can be divided into chronic rhinosinusitis without nasal polyps (CRSsNP) and chronic rhinosinusitis with nasal polyps (CRSwNP). Compared to CRSsNP, CRSwNP patients exhibited a higher comorbidity rate with asthma and a higher rate of revision surgery [2]. Additionally, the revision rate of CRSwNP patients is even further elevated in those with nasal colonization of Staphylococcus aureus (S. aureus) [3]. S. aureus and S. aureus-derived protein serine protease-like protein D (SplD) can induce thymic stromal lymphopoietin (TSLP) and IL-33 release from polyp tissues of CRSwNP, thereby propagating local type 2 inflammation [4,5]. It has been documented that macrophages play a pivotal role in bacterial elimination [6], and an elevated presence of CD206+macrophages in polyp tissues might be associated with the impaired phagocytosis of S. aureus [7]. This phagocytic deficiency of alternatively activated (M2a) macrophages contributes to the prolonged existence of S. aureus, exacerbating the ongoing inflammatory processes [8]. Therefore, further understanding macrophages could be beneficial for unveiling the mechanisms of bacterial clearance and chronic inflammation in CRSwNP.

Currently, the heterogeneity of macrophages is recognized by single-cell RNA sequencing (scRNA-seq). Eight subsets of tissue-resident macrophages (TRMs) and three subsets of tissue monocyte-derived macrophages (MDMs) have been identified within the polyp tissues of CRSwNP patients [9]. TRMs are known to play roles in tissue development and maintenance of homeostasis [10], while the recruitment of MDMs during inflammation tends to be connected to defense against pathogen invasion [11]. In this context, we focused on tissue MDMs in CRSwNP due to their critical functions in regulating inflammation in airways. Traditionally, ex vivo polarized MDMs such as classically activated (M1) macrophages and M2a macrophages have been used to mimic tissue MDMs for functional study in CRSwNP patients [12,13]. However, the extent to which these ex vivo polarized MDMs and tissue MDMs share phenotypic characteristics remains uncertain. Herein, further investigations are required to identify tissue MDMs and understand their regulatory role in bacteria elimination.

In this study, we validated the identification markers and characteristics of tissue MDMs in polyp tissues of CRSwNP patients. We also evaluated the correlations between the expression level of tissue MDMs and disease severity. To address the limited availability of tissue MDMs for functional studies, we explored the similarities and differences between tissue MDMs and ex vivo polarized MDMs to identify potential substitutes. Furthermore, we investigated the capacity of tissue MDMs to eliminate bacteria using suitable ex vivo polarized MDM substitutes. This research aimed to provide new insights into the roles of MDM subsets in maintaining sustained inflammation in polyp tissue.