Lysosomal Thiol Proteases (Cathepsin B-like Proteases) in Serous Middle Ear Effusions from Adult Patients

Abstract

Hydrolytic activity of cathepsins B, H and trypsimlike proteases was measured in 38 serous middle ear effusion (MEE) samples. The conc:entrations of al₁ antitrypsin (al₁-AT) and al₂-macroglobulin (al₂-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>0.005). Very low trypsin-like protease activity could be observed. The mean concentrations of al₁-AT and al₂-M were 368°94.8 mg/dl and 57.5°57.3 mg/dl. The bulk of al₁-AT in MEEs was occupied by free al₁-AT, which can saturate exogenous trypsin. Due to the very low molar concentration of al₂-M in MEEs, thiol proteases (mainly cathepsin E) could be a possible major factor inflicting proteolytic injury on the middle ear mucsa and reflecting the seventy of the inflammatory process.

Key Words:

• al₁-antitrypsin
• al₂-macroglobulin
• cathepsin B
• lysosomal thiol protease