Local immune response in the skin of the external auditory meatus: an immunohistochemical study

Cerumen plays an important role in the protection of the external auditory meatus against several kinds of damage. Its hydrophobic properties, due to the high concentration of lipids, shelter the canal from physical damages, while other components probably protect against certain microbial strains. Nevertheless there has been considerable dispute in the literature with regard to the antibacterial activity of cerumen. Because of the importance of the role of immunoglobulins (Ig) in local defense mechanisms, we attempted to study, by immunohistochemical methods, the presence and localization of the cells necessary to activate an Ig-mediated immune response and the epithelial expression of immunoglobulin A (IgA), immunoglobulin M (IgM), and immunoglobulin G (IgG) in order to obtain information about a local immune response in those areas of the skin that take part in cerumen production. Our findings indicate that in the human skin of the external auditory canal the cells necessary to activate an antibody-mediated immune response were localized in the different layers of the epidermis and/or in the dermis surrounding the sebaceous and ceruminous glands and the piliary follicle, while an intense immunoreactivity for IgA and IgG was observed in the epithelial layers of the skin. The results suggest that the external auditory canal is protected from the insults of pathogens by an antibody-mediated local immune response, because all the effector components of an active local immune system are present.