Secretory Immunoglobulin a (SIgA) in Middle Ear Effusions; A Further Report

Immunochemical and immunofluorescent studies of secretory immunoglobulin A (SIgA) in otitis media with effusion were carried out to investigate the local immunologic defense system and secretory activity in the middle ear. SIgA was isolated from pooled middle ear effusions by an immunoadsorbents technique and its antigenicity and subunit structure compared with SIgA derived from other external secretions, such as saliva, nasal discharge, and colostrum. The antigenicity and subunit structure of the isolated SIgA from middle ear effusions were identical or very similar to those of SIgA obtained from other external secretions. Radioimmunodiffusion analysis revealed that SIgA was present in 43 of 47 (91.5%) cases of serous middle ear effusion, whereas the sera from only 3 of 47 (6.4%) of these patients was found to have SIgA. Immunoelectrophoresis, using anti-SIgA antiserum, and radioimmunoelectrophoresis detected free SC (secretory component) in 1 of 47 (2%) serous and 6 of 30 (20%) mucoid effusions. Apices of epithelial cells and glandular acinar cells of the middle ear mucosa obtained from patients with otitis media with effusion were stained specifically with anti-SC antibodies. Findings of the study would suggest: 1) that the middle ear maintains the local immunologic defense system, as do respiratory tracts and salivary glands, and 2) that while serous middle ear effusions are a mixture of normal middle ear secretions bathing the membrane surface and transudates from serum, mucoid effusions are the result of enhanced epithelial secretory activity and transudates.