Background/Objectives: Airway granulation tissue is a common, recurrent problem occurring in patients with iatrogenic laryngotracheal stenosis (iLTS) due to chronic mucosal irritation from indwelling tracheostomy tubes. In iLTS, increased alternatively activated (M2) macrophages are present and promote fibrosis, however the phenotype of macrophages in upper airway granulation tissue is unknown. The objective of this study is to define the macrophage population in granulation tissue associated with iLTS.
Methods: Granulation tissue biopsies were obtained from 8 patients with iLTS. Cell type analysis was performed by flow cytometry and gene expression was measured by PCR. These methods were used to define the macrophage population in granulation tissue and were compared to healthy tracheal mucosa from rapid autopsy specimens.
Results: Flow cytometry of iLTS granulation tissue demonstrated macrophages (CD45+CD68+) represent 7.59% of the cell population. Tissue resident macrophages (CD169+) represent 1.65% of this population. Of macrophages expressing the M1 marker (CD86) or the M2 marker (CD206), 99.2% demonstrated an M2 phenotype. Additionally, 18.9% expressed the pro-inflammatory molecule S100A8/A9. M2 gene expression (Arginase 1 and CD206) was significantly increased in granulation tissue compared to controls (9.3±2.7, p=0.035 and 10.4±4.1, p=0.047). M1 gene expression (CD80 and CD86) was similar in granulation specimens and controls (p=0.64 and p=0.30).
Conclusions: Alternatively activated M2 macrophages are the dominant macrophage type in iLTS granulation tissue, however the factors leading to pathogenic macrophage polarization are unclear. The role of this cell type in promoting ongoing inflammation and fibrosis warrants future investigation to identify potential treatment strategies for airway granulation tissue.