Passive transfer of immune-mediated middle ear inflammation and effusion

Antigenic challenge in the middle ear of animals previously sensitized intradermally results in an immunologically mediated inflammatory response, including the generation of serous effusion in the middle ear cavity. The mechanisms which contribute to this immune-mediated otitis media with effusion (OME) were investigated by passive transfer with either purified IgG or with sensitized lymphocytes. A peritoneal exudate was raised in strain 13 guinea pigs by repeated injection of keyhole limpet hemocyanin (KLH) with complete Freund's adjuvant. IgG and lymphocytes were isolated from exudates and used for passive sensitization. Middle ear challenge following passive transfer of IgG specific to KLH produced effusion and inflammation which was equivalent to that observed in actively immunized animals, but resulted in significantly greater numbers of leukocytes infiltrating the middle ear. Unlike in the active response, few of the cells infiltrating the middle ear mucosa and middle ear cavity were eosinophils. Middle ear challenge with KLH following passive transfer with sensitized lymphocytes produced no middle ear effusion, relatively little mucosal inflammation, and sharply reduced exocytosis of leukocytes into the middle ear when compared with the active immune response or even with unimmunized controls. It is concluded that middle ear effusion, inflammation, and leukocytic exocytosis are mediated primarily by the IgG fraction of humoral immunity in our model of immune OME.