M2 Macrophages Promote Collagen Expression and Synthesis in Laryngotracheal Stenosis Fibroblasts

Abstract

Objective Macrophages exhibit distinct phenotypes and are dysregulated in a model of iatrogenic laryngotracheal stenosis (iLTS). Increased populations of alternatively activated or M2 macrophages have been demonstrated. However, the role of these macrophages is unknown. The aims of this study are: 1) define the macrophage population in iLTS in the context of classically activated or M1 and M2 macrophage phenotypes, and 2) characterize the effect of monocyte‐derived M1 and M2 macrophages on normal airway and LTS‐derived fibroblasts (FBs) in vitro. Study Design Comparative analysis; in vitro controlled study. Methods Immunohistochemical analysis of human iLTS and control specimens was performed to define the macrophage population. In vitro, M1, and M2 macrophages were polarized using M‐CSF + Interferon‐gamma and lipopolysaccharide or Interleukin‐4, respectively. FBs isolated from laryngotracheal scar (LTS‐FBs) and normal tracheal airway (NA‐FBs) in eight patients with iLTS were cocultured with polarized macrophages. Fibrosis gene expression, soluble collagen production, and proliferation were assessed. Results Immunohistochemical analysis revealed increased CD11b + cells (macrophage marker) in laryngotracheal scar specimens (18.3% vs. 8.5%, P = .03) and predominant CD206 (M2) costaining versus CD86 (M1) (51.5% vs. 9.8%, n = 10, P = .001). In vitro, NA‐FBs cultured with M2 macrophages demonstrated a 2.41‐fold increase in collagen‐1 expression (P = .05, n = 8) and an increase in soluble collagen (9.98 vs. 8.875, mean difference: 1.11 95%, confidence interval 0.024–2.192, n = 8, P = .015). Conclusion Increased populations of CD11b cells are present in iLTS specimens and are predominantly CD206+, indicating an M2 phenotype. In vitro, M2 macrophages promoted collagen expression in airway FBs. Targeting macrophages may represent a therapeutic strategy for attenuating fibrosis in iLTS. Level of Evidence NA Laryngoscope, 131:E346–E353, 2021

An Updated Review of Subglottic Stenosis: Etiology, Evaluation, and Management

“…In iatrogenic LTS, fibroblasts have been demonstrated as the predominant effector cell in fibrogenesis [15][16][17]. Recently, macrophages, specifically of the M2 phenotype, were found at high levels in iatrogenic LTS specimens and demonstrated to induce collagen production by fibroblasts [18]. By studying mice with severe combined immunodeficiency, Ghosh et al were able to demonstrate that systemic circulating mediators, T cells, and B cells all play roles in initiating granulation tissue formation in response to tissue injury, as opposed to resident airway immune cells alone.…”

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“…Recently, Motz K et al described an increased number of M2 macrophages in an immunohistochemical analysis of human laryngotracheal scar specimens. In the same study, they also showed that in vitro M2 macrophages favoured aberrant fibroblasts behaviour and promoted tracheal fibroblasts to express and produce collagen [ 37 ]. These findings are consistent with similar investigations on other fibrotic diseases which underline the potential role of M2 inflammation in aberrant ECM deposition, especially in IPF and cardiac fibrosis [ 38 , 39 ].…”

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