Serum immunoreactive prolyl hydroxylase in inflammatory rheumatic diseases

Serum immunoreactive prolyl hydroxylase protein (S-IRPH) was measured in 56 patients with inflammatory rheumatic diseases, and the values were compared with those in 32 control subjects. S-IRPH was above the 95% confidence limit of the controls in about 70% of the patients with active systemic lupus erythematosus, rheumatoid arthritis, scleroderma, Reiter's syndrome, Sjögren's syndrome, polyarteritis nodosa, or polymyositis. Raised values were observed in about half of the patients with an erythrocyte sedimentation rate (ESR) of 21-50 and in about 90% of those with ESR of over 50, whereas only about 10% of the patients with an inactive disease had an S-IRPH concentration exceeding this limit. Only 1 out of 8 patients with active ankylosing spondylitis had a raised S-IRPH value. The results support previous data indicating that significant changes in collagen metabolism occur in active connective tissue diseases. Assays of S-IRPH might be of some value in assessing the activity of these diseases and in monitoring the treatment provided.