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

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.