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

The sites of alkaline phosphatase (ALP) activity of the synovial membrane were demonstrated by enzyme histochemistry in eight patients with rheumatoid arthritis, eleven patients with other joint diseases, and six control patients with normal synovial membrane who underwent surgery for traumatic injuries of the periarticular tissues. ALP activity of the lining cells of the synovial membrane was intense in patients with rheumatoid arthritis and moderate in control patients. The collagen-rich stroma and the underlying vessels, major sites of synovial proliferation in rheumatoid arthritis, were also intensely positive for ALP in this disease. Selected ALP-positive cells located within the superficial lining and the stroma were identified as macrophages. ALP activity was low in cases of osteoarthritis. These findings support the views: (1) that ALP activity is produced by synovial membrane tissue components; and (2) that it is an indicator of synovial proliferation and inflammation in rheumatoid arthritis.