Effects of endotoxin and neutrophil lysate on experimental otitis media with effusion in cats

Middle ear effusion (MEE) from otitis media with effusion (OME) contains large amounts of chemical mediators and substances from bacteria, which may act on the mucosa itself and cause further changes in the inflamed mucosa and MEE. To clarify the effects of such substances in MEE, we instilled endotoxin (LPS) or allogeneic neutrophil lysate (NL) into the middle ear cavity of OME induced by Eustachian tube obstruction (ETO). ETO + LPS and ETO + NL groups showed retention of a large amount of MEE as a characteristic difference between ETO alone group and these groups. The instillation of LPS into the middle ear cavity of the ETO model significantly increased the number of total cells and the ratio of the concentrations of albumin to total protein in MEEs. The instillation of NL significantly increased the number of goblet cells in the middle ear. These facts indicate that the pathology of OME may change in response to various factors added to MEE. Hence, we propose that a vicious circle of self-mediated inflammation is a possible causative factor for chronic OME.