ALKALINE-PHOSPHATASE ACTIVITY OF THE SYNOVIAL-MEMBRANE IN RHEUMATOID-ARTHRITIS

The sites of alkaline phosphatase (ALP) activity of the synovial membr ane were demonstrated by enzyme histochemistry in eight patients with rheumatoid arthritis, eleven patients with other joint diseases, and s ix control patients with normal synovial membrane who underwent surger y for traumatic injuries of the periarticular tissues. ALP activity of the lining cells of the synovial membrane was intense in patients wit h rheumatoid arthritis and moderate in control patients. The collagen- rich stroma and the underlying vessels, major sites of synovial prolif eration in rheumatoid arthritis, were also intensely positive for ALP in this disease. Selected ALP-positive cells located within the superf icial lining and the stroma were identified as macrophages. ALP activi ty was low in cases of osteoarthritis. These findings support the view s: (1) that ALP activity is produced by synovial membrane tissue compo nents; and (2) that it is an indicator of synovial proliferation and i nflammation in rheumatoid arthritis.