Spatial distribution of antimicrobial peptides and mast cells in the skin of the external auditory canal

Comparative study of the external auditory canal in humans and large mammals

Given the limited source of human external auditory canal (EAC) skin, animal experiments remain an important approach for studying functional EAC reconstruction. However, differences between humans and animals in terms of the general EAC structure, histological characteristics of EAC skin, and cell markers of its specific glands in cartilaginous EAC skin remain unknown. We compared the characteristics of the EAC between humans and large animals, as a basis for appropriate animal model selection. Temporal bone computed tomography was used to compare the EACs of humans, goats, pigs, and dogs. EAC skin samples were harvested and their histological characteristics evaluated. The skin's ultrastructure and the histological structure of specific glands and cell markers related to cell phenotype and function were further identified. The EAC structure in goats was similar to that in humans in terms of diameter, length, and cartilaginous segment ratio of the EAC, while that of pigs and dogs differed markedly. Furthermore, histological evaluation showed that there were abundant ceruminous and sebaceous glands in the goat's cartilaginous skin, while dogs and pigs showed notably fewer of these glands in cartilaginous skin than humans. Nevertheless, ceruminous glands in all species studied showed similar expression of cell biomarkers and secretion function. Goats might have advantages in terms of surgery and reconstruction of the functional EAC skin compared to dogs and pigs and can be a useful candidate for ceruminous gland cell sources.

Substance P and Calcitonin Gene-Related Peptide in the Glands of External Auditory Canal Skin

Objectives

The earwax (cerumen) that covers external auditory canal (EAC) skin contains a mixture of ceruminous and sebaceous gland substances, such as lipids, peptides, and proteins. The components secreted from the ceruminous gland that is a modified sweat gland form cerumen and contain several antimicrobial factors. Since substance P (SP) and calcitonin gene-related peptide (CGRP), known as a secretagogue, have been found in sweat glands, our purpose was to determine the expression of SP and CGRP in the glands of EAC skin.

Methods

Sections of normal human EAC skins were immunostained for the presence of SP and CGRP using polyclonal antibodies. Immunoreactivity was detected using an avidin-biotin peroxidase complex method.

Results

SP staining was found in ceruminous gland acini and myoepithelial cells. But the SP staining was not found in the sebaceous glands and epidermal region. CGRP was strongly stained in the ceruminous gland and weakly in the sebaceous gland cells. Interestingly, most prominent staining of SP and CGRP was noted in the myoepithelial cells of the ceruminous gland.

Conclusion

The findings in this study suggest that SP and CGRP are expressed in the glands of the EAC skin and secreted in the process of ceruminous gland secretion.

Studies on distribution of α1-antitrypsin, lysozyme, lactoferrin, and mast cell enzymes in diseased middle ear mucosa

CONCLUSION

Antimicrobial agents (AMAs) and mast cells in chronic otitis media (COM) may play a protective role in the pathogenesis of COM. Among them, our results indicated that lysozyme may be the most important parameter of the mucosa infectivity in COM.

OBJECTIVES

AMAs include alpha 1-antitrypsin (α1-AT), lysozyme, and lactoferrin and exhibit innate immune activity that is known to play a critical role in mucosal defenses. In addition, proteases expressed in mast cells contribute to mucosal defenses. The aim of this study was to identify AMAs responsible for COM as well as their association with middle ear mucosal diseases.

METHODS

Middle ear mucosa (MEM) was intraoperatively collected by biopsy from patients, diagnosed as COM without or with cholesteatoma, and immediately processed for immunohistochemical study to evaluate expression of AMAs and mast cell proteases (chymase and tryptase).

RESULTS

The AMAs and mast cell enzymes were observed prominently in the chronic middle ear diseases whereas immunoreactivity of α1-AT and lysozyme was not significantly increased in the COM with cholesteatoma compared with that in COM without cholesteatoma. Lactoferrin was not detected in the diseased MEMs.