Immunohistochemical quantitation of collagen types I, II, IV and V in the ventilated and non-ventilated rabbit middle ear with otitis media with effusion.

Morphometric quantitation of the area fractions of collagen types I, II, IV and V was determined in the normal rabbit middle ear mucosa and in relation to otitis media with effusion (OME) using a three-layered peroxidase-antiperoxidase technique. The effects of substituting normal low-oxygen middle ear gas (non-ventilated) with atmospheric air (ventilated) were studied in both healthy ears and ears with OME. Based upon previous histological examinations in rabbits, only ears with OME for more than 8 weeks were included to ensure the presence of chronic inflammation (COME). Atmospheric air was introduced into the middle ears by insertion of ventilation tubes or by an enlarged myringotomy. Collagen type I was predominant in all groups studied. The area fractions of collagen types I, II and IV were increased significantly in COME, with collagen type II elevated in particular. Ventilation of the normal ears resulted in a significantly increased area fraction of cells, while the area fractions and distributions of the collagen types were unaffected. None of the ventilated ears in COME improved or healed spontaneously. The total fraction of collagen in COME was not changed significantly by the introduction of atmospheric air. However, the individual distribution of the collagen types was altered, with significantly larger area fractions of types II and V found in ventilated ears with COME. Possible explanations for the differences found are discussed, including the role of oxygen-derived free radicals.