Myeloid Phenotypes in Tracheostomy-Associated Granulation Tissue

Objective(s):Tracheostomy-associated granulation tissue is a common, recurrent problem occurring secondary to chronic mucosal irritation. Although granulation tissue is composed of predominantly innate immune cells, the phenotype of monocytes and macrophages in tracheostomy-associated granulation tissue is unknown. This study aims to define the myeloid cell population in granulation tissue secondary to tracheostomy. Methods:Granulation tissue biopsies were obtained from 8 patients with tracheostomy secondary to laryngotracheal stenosis. Cell type analysis was performed by flow cytometry and gene expression was measured by quantitative real-time polymerase chain reaction. These methods and immunohistochemistry were used to define the monocyte/macrophage population in granulation tissue and were compared to tracheal autopsy control specimens. Results:Flow cytometry demonstrated macrophages (CD45+CD11b+) and monocytes (CD45+(FSCSSClow)-S-low) represent 23.2 & PLUSMN; 6% of the granulation tissue cell population. The M2 phenotype (CD206) is present in 77 +/- 11% of the macrophage population and increased compared to the M1 phenotype (p = 0.012). Classical monocytes (CD45+CD14(high)CD16(low)) were increased in granulation tissue compared to controls (61.2 +/- 7% and 30 +/- 8.5%, p = 0.038). Eighty-five percent of macrophages expressed pro-inflammatory S100A8/A9 and 36 +/- 4% of macrophages co-localized CD169, associated with tissue-resident macrophages. M2 gene expression (Arg1/CD206) was increased in granulation tissue (3.7 +/- 0.4, p = 0.035 and 3.5 +/- 0.5, p = 0.047) whereas M1 gene expression (CD80/CD86) was similar to controls (p = 0.64, p = 0.3). Immunohistochemistry of granulation tissue demonstrated increased cells co-localizing CD11b and CD206. Conclusions:M2 macrophages are the dominant macrophage phenotype in tracheostomy-associated granulation tissue. The role of this cell type in promoting ongoing inflammation warrants future investigation to identify potential treatments for granulation tissue secondary to tracheostomy.