Spontaneous development of otitis media in plasminogen-deficient mice.

Inflammatory conditions of the ear, otitis media, are one of the most common disease entities in children. In this study, the role of the plasminogen (plg)/plasmin system for the spontaneous development of chronic otitis media was investigated by the analysis of plg-deficient mice. Whereas essentially all of the wild-type control mice kept a healthy status of the middle ear, all the plg-deficient mice gradually developed chronic otitis media with various degrees of inflammatory changes during an 18-week observation period. Five bacterial strains were identified in materials obtained from the middle ear cavities of six plg-deficient mice. Morphological studies revealed the formation of an amorphous mass tissue and inflammatory changes in the middle ears of plg-deficient mice. Immunohistochemical studies further indicate a mass infiltration of neutrophils and macrophages as well as the presence of T and B cells in the middle ear mucosa of these mice. Extensive fibrin deposition and an abnormal keratin formation were also observed in the tympanic membrane, the middle ear cavity and external ear canal in these mice. These results suggest that plg plays an essential role in protecting against the spontaneous development of chronic otitis media. Our findings also suggest the possibility of using plg for clinical therapy of certain types of otitis media.