Reduced amyloid-A-degrading activity in serum in amyloidosis associated with rheumatoid arthritis

Abstract

The ability to degrade amyloid A fibrils was studied in the serum of 31 patients with amyloidosis associated with rheumatoid arthritis, 33 patients with rheumatoid arthritis without amyloidosis, and 47 healthy controls. Fibrillar amyloid A protein and the radial diffusion method were used. The mean degrading activity in serum was significantly lower in patients with rheumatoid arthritis complicated by amyloidosis (58±19% SD of the activity in a pooled sample of sera from 100 healthy blood donors used as standard) than in patients with rheumatoid arthritis alone (78 ±14%; p < 0-001) or controls (99±19%; p < 0001). Alpha.-antitrypsin, concentrations of which were raised in both groups of patients, inhibited the degrading activity in serum even in low concentrations. A negative correlation between degrading activity and alpha,-antitrypsin concentrations was observed. These findings suggest that reduced amyloid-A-degrading activity is due to inhibition rather than to deficiency of enzyme. © 1982, British Medical Journal Publishing Group. All rights reserved.