Human ceruminous gland: ultrastructure and histochemical analysis of antimicrobial and cytoskeletal components

Abstract

The ceruminous glands in the skin of the human external auditory canal are modified apocrine glands, which, together with sebaceous glands, produce the cerumen, the ear wax. Cerumen plays an important role in the protection of the ear canal against physical damage and microbial invasion. We studied the morphology of the glandular cells by light and electronmicroscopy. Antimicrobial and cytoskeletal components of the ceruminous glands were investigated by immunohistochemical methods. Numerous antimicrobial proteins and peptides are present in the ceruminous glandular cells: beta-defensin-1, beta-defensin-2, cathelicidin, lysozyme, lactoferrin, MUC1, secretory component of IgA. These data indicate a crucial role in the innate host defense against diverse pathogens. The apocrine secretion mechanism is a special mode of secretion by which the apical part of the cell cytoplasm surrounded by a membrane is pinched off. We could show that the presence of actin filaments, CK 19 and CK 7, seems to play a role in the pinching-off mechanism. Finally, we showed the secretion of lipid vesicles from the ceruminous gland. We could extend the number of detected antimicrobial peptides and proteins in human ceruminous glandular cells that protect the surface of the external auditory meatus. In addition, we detected proteins involved in the apocrine secretion mode of the ceruminous gland.