The Leukocyte Protein L1 in Plasma and Synovial Fluid from Patients with Rheumatoid Arthritis and Osteoarthritis

Abstract

Berntzen HB, Ölmez U, Fagerhol MK, Munthe E. The Leukocyte Protein L1 in Plasma and Synovial Fluid from Patients with Rheumatoid Arthritis and Osteoarthritis. Scand J Rheumatol 1991; 20: 74-82.

L1 is a major granulocyte and monocyte protein, released during activation and turnover of such cells. Blood and synovial fluid (SF) from 41 patients with rheumatoid arthritis (RA) and 6 patients with osteoarthritis (OA), were analyzed for L1 and the acute phase proteins C-reactive protein, orosomucoid, haptoglobin, α₁-antitrypsin and albumin as well as for differential leukocyte count. L1 levels in plasma and SF showed highly significant differences (p < 0.0001), between the RA and OA patients. All the OA patients had norma! plasma concentrations of L1 and low concentrations of L1 in SF. All the RA patients had elevated plasma levels of L1 and high L1 concentrations in SF. In the RA patients, the ratios between the protein concentrations in SF and blood were 3.29 for L1 and ≤ 0.64 for the acute phase proteins. In the SF, the L1 levels did not correlate with the monocyte count, while a low, positive correlation was found between L1 and the granulocyte count. The high L1 concentrations observed in SF from RA patients probably reflected an increased turnover of leukocytes in the inflamed joints. In SF from RA patients, high L1 concentrations were found in joints with a high amount of swelling. The present study suggests that L1 may represent a marker of both local and systemic inflammation.

This work has been supported by a Syntex scholarship in rheumatology

Key Words:

• The L1 protein
• calprotectin
• acute phase proteins
• rheumatoid arthritis
• osteoarthritis
• synovial fluid