Plasmin and fibronectin degradation in chronic secretory otitis media

Mucoid effusions from 39 children with secretory otitis media, altogether 42 specimens, were analyzed for proteolytic activity using radial caseinolysis procedures, for fibronectin using a solid-phase enzyme immunoassay, and for fibronectin fragmentation using immunoblotting. All samples contained proteolytic activity, tentatively identified as plasmin on the basis of comigration with purified human plasmin in zymographic analysis. In 19 specimens the plasmin level exceeded 1 microgram/mg of protein; the highest value recorded was 18.7 micrograms/mg. Low levels of net plasminogen activator activity were found in 12 specimens and identified as urokinase according to comigration with the urokinase standard in zymography. Fibronectin was detected in all but one of the 42 specimens; in seven specimens the levels exceeded those in normal plasma, calculated per milligram of total protein. Extensive fragmentation of fibronectin was found in 19 specimens, correlating with high plasmin levels. The results are indicative of an ongoing proteolytic process in secretory otitis media and suggest that plasmin-caused degradation of the fibronectin-containing basement membrane and subsequent formation of granulation tissue may be involved in the development of adhesive middle ears.