Innate immunity and the role of defensins in otitis media

Abstract

Otitis media is the most common pediatric disease in developed countries and a significant cause of morbidity and hearing loss in developing countries. The innate immune system is essential to protecting the middle ear from infection. Defensins, broad-spectrum cationic antimicrobial peptides, have been implicated in prevention of and the early response to acute otitis media; however, the mechanisms by which defensins and other antimicrobial molecules mediate this protection have not been completely elucidated. In both animal otitis media models and human middle ear epithelial cell culture models, β-defensins are highly induced and effectively kill the common pathogens associated with otitis media. We review the importance of innate immunity in protecting the middle ear and recent advances in understanding the roles of defensins and other antimicrobial molecules in the prevention and treatment of otitis media. The extremely high prevalence of otitis media, in spite of sophisticated innate and adaptive immune systems, is a vexing problem for clinicians and scientists. We therefore also review mechanisms by which bacteria evade innate immune defenses.

Fig 1

Innate immunity and the middle ear. Innate immunity includes barrier functions, sensing of pathogenic bacteria (by receptors on and in epithelial cells, dendritic cells, and mast cells), release of antimicrobial peptides and proteins, and recruitment and activity of various effector cells (eg, neutrophils, macrophages, fibroblasts, natural killer cells, and eosinophils)