High-mobility group box protein 1 expression in inflammatory diseases of the middle ear

Abstract

High-mobility group box 1 (HMGB1) is a nuclear non-histone protein, playing a critical role as a mediator between innate and acquired immunity; when released extracellularly, it coordinates the cellular stress response (under necrosis, bacterial lipopolysaccharide stimulation) and acts as an inflammatory marker and cytokine. The aim of the study was to demonstrate whether HMGB1 is over-expressed in chronic middle-ear pathologies and whether the entity of expression and the localization are correlated with the degree of the inflammatory reaction, thus suggesting that HMGB1 may play a crucial role in chronic inflammatory disorders of the middle ear, as already demonstrated in other airway diseases. We analyzed 30 samples of middle-ear mucosa in patients affected by chronic suppurative otitis media with ear drum perforation with/without cholesteatoma and otosclerosis as control. The distribution of HMGB1 was evaluated as nuclear, cytoplasmic, and/or extracellular staining. The inflammatory cells observed in the biopsies were mostly lymphocytes and plasmacells. A statistically significant difference in inflammation score between otosclerosis and chronic otitis samples ( P < 0.01; Anova test) and between otosclerosis and cholesteatoma samples ( P < 0.05; Anova test) was observed; the HMGB1 positivity was in accordance with the density of the inflammatory infiltrate. HMGB1 is over-expressed in chronic middle-ear pathologies and may play a role in the progression of the inflammatory process from recurrent acute otitis media to chronic suppurative otitis media.

Keywords: cholesteatoma; high-mobility group box 1 (HMGB1); inflammation; otosclerosis.

Figure 1.

Semi-quantitative analysis of intensity of inflammation. Intensity of inflammation is measured as a score in middle ear mucosa of three pathology groups (Anova test). Inflammatory infiltrate is very low in otosclerosis (0.5%) and high in COM (2.3%) and cholesteatoma (1.9%).

Figure 2.

Inflammatory infiltrate and HMGB1 positivity in epithelial and endothelial cells of middle-ear mucosa in patient with (a, b) otosclerosis, (c, d) cholesteatoma, and (e, f) COM. Scale bars: 10 µm. Each section was stained with H&E and subjected to immunohistochemistry (IHC) for HMGB1 detection. (a) Otosclerosis : cubical epithelium and underlying chorion with a minimal inflammatory infiltrate. H&E, 200×; (b) HMGB1 positivity in epithelial and endothelial cells. IHC, 200×; (c) ciliated pseudostratified columnar epithelium and underlying chorion with inflammatory infiltrate composed by lymphocytes, plasmacells, histiocytes, and polymorphonucleated. H&E, 200×; (d) nuclear positivity in epithelial and inflammatory cells. IHC, 200×; (e) copious inflammatory infiltrate, composed of lymphocytes, plasmacells, and neutrophils. Also present is a gland with cubical epithelial cells, correlated to inflammation. H&E, 200×; (f) strong HMGB1 positivity in epithelial and inflammatory cells with prevalently nuclear distribution. IHC, 200×.