Expression of osteopontin by exudate macrophages in inflammatory tissues of the middle ear: a possible association with development of tympanosclerosis.

Tympanosclerosis is a condition leading to a calcification process in the middle ear, and often develops after chronic inflammation of the middle ear. Since osteopontin (OPN) has been shown to participate in the pathological calcification, we here investigated whether OPN is involved in the process of calcification in tympanosclerosis. The tympanic membrane and middle ear mucosa, obtained from patients of tympanosclerosis and chronic otitis media, were histologically classified depending on the calcification degree. In hyalinized tissues with macroscopic calcification and fibrous tissues with microscopic calcification, OPN was immunohistochemically found in the calcification sites. In inflammatory tissues with microscopic calcification, OPN was also found in the calcifying foci, and many OPN mRNA-expressing cells, determined by in situ hybridization, located around their foci. Moreover, immunohistochemical double staining of OPN and CD68 showed that the OPN-expressing cells were CD68-positive, indicating these cells were macrophages. In inflammatory tissues without calcification, immunohistochemistry of CD68 and in situ hybridization of OPN mRNA revealed that most OPN mRNA-expressing cells were CD68-positive. The expression of OPN mRNA in inflammatory tissues was also shown by reverse transcriptase polymerase chain reaction. These results suggest that OPN secreted by exudate macrophages might be an important regulator in the calcification of tympanosclerosis.