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Endotoxin levels and lysosomal protease (collagenase, cathepsin B, and lysozyme) activity were measured in 104 middle ear effusions (MEEs) from patients with otitis media with effusion (OME). The MEE samples were classified into four groups: pediatric serous, mucoid, and acute, and adult serous. Endotoxin levels and lysosomal protease activity in MEEs were significantly different in the following order: adult less than serous less than mucoid less than acute groups, indicating that both endotoxin and lysosomal proteases are more closely related to the pathogenesis of pediatric chronic OME than to adult OME. In pediatric serous and mucoid effusions, endotoxin level had a significant correlation with activity of the lysosomal proteases. In conclusion, endotoxin enhances leukocyte infiltration into the middle ear, and lysosomal proteases released from leukocytes damage the middle ear mucosa and thereby prolong mucosal inflammation, which may be responsible for delayed recovery from acute OME.

Hydrolytic activity of cathepsins B, H and trypsin-like proteases was measured in 38 serous middle ear effusion (MEE) samples. The concentrations of (alpha 1-AT) and alpha 2-macroglobulin (alpha 2-M) were also quantitated. The mean value of cathepsin B activity was 25.0 +/- 20.7 RFU and that of cathepsin H was 14.3 +/- 3.0--both significantly higher than those in plasma (1.8 +/- 0.4 RFU, 1.2 +/- 0.3 RFU, p less than 0.005). Very low trypsin-like protease activity could be observed. The mean concentrations of alpha 1-AT and alpha 2-M were 368 +/- 94.8 mg/dl and 57.5 +/- 57.3 mg/dl. The bulk of alpha 1-AT in MEEs was occupied by free alpha 1-AT, which can saturate exogenous trypsin. Due to the very low molar concentration of alpha 2-M in MEEs, thiol proteases (mainly cathepsin B) could be a possible major factor inflicting proteolytic injury on the middle ear mucosa and reflecting the severity of the inflammatory process.

We analyzed the composition of glycoproteins in serous and mucoid middle ear effusions (MEE) collected from patients with chronic otitis media with effusion (OME), and compared this with plasma glycoproteins, using rectin-conjugated sepharose. The concentration ratio of rectin-absorbed glycoproteins to total protein concentration in serous MEE resembled that in plasma, although mucoid MEE had a higher concentration ratio than that of the serous effusions. By SDS-polyacrylamide gel electrophoresis analysis, the molecular weight pattern of glycoproteins adsorbed to wheat germ agglutinin (WGA) gel in serous MEE was more similar to that in plasma than in the mucoid effusions. Using 2-mercaptoethanol, the basic low-molecular-weight components of the glycoproteins were almost identical in MEE and in plasma. Our findings show that mucoid MEE has a greater amount of plasma and epithelial glycoproteins than does serous fluid. The composition of these latter substances is more similar to that of plasma glycoproteins. The strong disulfide bonds present in glycoproteins may significantly contribute to the physicochemical properties of mucoid MEE.

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