Complement in chronic secretory otitis media. C3 breakdown and C3 splitting activity.

Occurrence of in vivo C3 breakdown and in vitro C3 splitting activity was studied in serum and middle-ear effusion (MEE) samples from 30 children with chronic secretory otitis media (SOM). The MEE showed strongly elevated levels of both low- and high-molecular-weight C3 breakdown products, along with decreased factor B, C4, and C3 levels. Total hemolytic complement component activity was virtually absent from MEE. The MEE fluids were found to contain C3 splitting factors as demonstrated by their high capacity to convert C3 in vitro from fresh normal human serum. This activity was not inhibited by the classic complement pathway inhibitor, 0.01M ethylene glycol tetra-acetic acid with 0.005M magnesium chloride. The results suggest that a strong local complement activation has taken place and that the factors responsible are present in the MEE of patients with SOM.