Biological property of immune complex to prolong the duration of otitis media with effusion.

This study was designed to evaluate the biological properties of a light molecular weight immune complex, in comparison with that of a heavy molecular weight immune complex. Soluble immune complexes were obtained by mixing horseradish peroxidase (HRP) with guinea pig antiserum to HRP and were divided by gel filtration into several fractions according to their molecular weight (MW). After the chemotactic activity of each fraction was examined in vitro, the lightest and the heaviest MW immune complexes were injected into a guinea pig's left and right superior bulla, respectively. Although a middle ear effusion developed in both the bulla, the histopathological feature of an experimentally induced otitis media with effusion varied with the MW of the injected immune complex. The light MW immune complex proved to be a stronger inducer for a macrophage than the heavy MW immune complex, both in vitro and in vivo, and to have a tendency to persist longer in the tympanic cavity than the heavy MW immune complex. These results suggested that otitis media had a tendency to persist when a light MW immune complex was formed in a middle ear. The light MW immune complex was suspected to be involved in the pathogenesis of otitis media with effusion.