Investigation of respiratory surfactant A protein in middle ear epithelium

Abstract

Introduction: The middle ear of mammals is an air-chamber required for sound transmission. It is lined by an epithelium which is variable but which resembles that of the lungs. Lung function depends upon surfactant which is a family of surfactant proteins which have an important role in breathing as well as infection control. Given that both the middle ear and the lungs can suffer collapse as well as infection, it is worth exploring whether surfactant protein is expressed throughout the middle ear in any manner analogous to that in the lung. Materials and methods: Our study has used simple histological stains to study cell and tissue morphology of the rodent middle ear. We used immunohistochemistry and protein electrophoresis to identify surfactant A protein as well as four cytokeratins expressed in lung cells. Results: We have demonstrated that surfactant protein A is indeed expressed in the middle ear and that there are cells which have a protein cytokeratin expression consistent with surfactant production and other cells whose cytokeratin expression reflects a likely role in gas exchange. Our research has also confirmed the presence of surfactant in the bone marrow spaces adjacent to the middle ear as well as other tissues reflecting its diverse roles. This also suggests a role in local and innate immunity. A novel finding was the presence of communications between the marrow spaces and the mouse middle ear cavity. Conclusion: These results suggest that there is a need for further work to assess the anatomical and topographical distribution of surfactant A protein throughout the variety of cell types within the middle ear. This will help to understand better the interaction of the various cell types in regard to the local and innate immunity of the middle ear as well as its gas exchange function.