1. Serum contains amyloid A-degrading activity. This activity is markedly reduced in patients with rheumatoid arthritis (RA) complicated by amyloidosis. α1-Antitrypsin inhibits the degradative activity. To test the hypothesis that the activity of this enzyme is regulated by α1-antitrypsin, we determined the concentrations, elastase-inhibitory activity and phenotypes of α1-antitrypsin in 24 RA patients with and in 26 RA patients without amyloidosis.
2. α1-Antitrypsin concentrations and biological activity were significantly increased in both patient groups compared with control subjects, but there was no difference between the two patient groups.
3. All patients who had developed amyloidosis were of the normal protease inhibitor (Pi) MM-phenotype.
4. We conclude that the difference in the amyloid A-degrading activity between RA patients with or without amyloidosis cannot be accounted for by differences in concentration, activity or Pi type of α1-antitrypsin.