Degradation of amyloid by a serum component and inhibition of degradation.

ADA of human serum was demonstrated and investigated with an agar gel diffusion technique using amyloid-impregnated agar plates. Sera of 20 healthy adults, 40 patients with AA-amyloidosis, and 86 nonamyloidotic patients were tested. The presence of an ADF, showing enzymatic properties and strongly bound to albumin, was demonstrated in normals and amyloidotic and nonamyloidotic patients. ADA in the serum of amyloidotic and cirrhotic patients was markedly decreased due to the presence of an inhibitor of ADF. ADA of amyloidotic sera was restored to normal by EDTA, citric acid, and ascorbic acid. The ADA of 16 FMF patients and four of 34 patients with rheumatoid arthritis without amyloidosis was intermediate between normal and amyloidotic values, indicating the presence of lADF at low concentrations in these patients. These findings suggest that amyloid is a normal protein metabolite, possibly with a high metabolic turnover. Accumulation of amyloid may be caused by decrease of the ADA of the serum by its inhibitor, rather than by accelerated production.