Soluble urokinase plasminogen activator receptor in plasma of patients with inflammatory rheumatic disorders: increased concentrations in rheumatoid arthritis

Objective-Urokinase type plasminogen activator (uPA) catalyses the formatio n of the proteolytic enzyme plasmin, which is involved in matrix degradatio n in the processes of tissue remodelling. Because of a surface bound uPA re ceptor (uPAR), expressed by some cell types (for example, macrophages, mali gnant cells and inflammatory activated synoviocytes), the action of uPA can be localised and intensified. uPAR seems to have a role in the mechanisms leading to invasive growth of malignant tissue and the rheumatoid pannus. u PAR may become cleaved at its cell surface anchor, thus forming a free solu ble receptor (suPAR). suPAR is detectable in low but constant values in pla sma of healthy people, while increased concentrations are found in patients with disseminated malignant disease, so that suPAR may be an indicator of invasive growth and tissue remodelling. suPAR concentrations in plasma have not previously been measured in rheumatic patients. A controlled cross sec tional measurement was performed of suPAR in plasma of patients with variou s inflammatory rheumatic disorders with special reference to rheumatoid art hritis (RA). Methods-suPAR in plasma was measured by ELISA technique in patients with RA (n=51), reactive arthritis (ReA) (n=23), primary Sjogren's syndrome (PSS) (n=42) and sex and age matched healthy controls (n=53). Results-In the control group suPAR (median) was 0.91 (range 0.56-1.94) mu g /l. Median suPAR value in RA was 1.47 (range 0.65-6.62) mu g/L; in ReA 0.68 mu g/l (range 0.52-1.48) and in PSS 1.12 mu g/l (range 0.76-1.92); p versu s controls <0.001 in all patient groups. suPAR values in RA were also signi ficantly increased compared with ReA (p<0.001) and PSS (p=0.004) groups. su PAR in RA was positively correlated to C reactive protein (CRP) (p<0.01) an d erythrocyte sedimentation rate (p<0.05) and number of swollen joints (p<0 .05). The ReA group had the highest CRP values of all groups, but at the sa me time the lowest suPAR concentrations in plasma. Conclusions-Increased suPAR concentrations were found in plasma in RA, and to a smaller extent also in PSS, but not in were also pared ReA. In RA suPA R is related to disease activity. suPAR seems though not merely to be an ac ute phase reactant like CRP. Increased suPAR values might reflect erosive a ctivity in RA.