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Human cathepsin G (EC 3.4.21.20) has been reported to have the in vitro chemotactic activity for human monocytes. In this study, we examined the role of cathepsin G in monocyte involvement in joint inflammation of rheumatoid arthritis (RA) as a monocyte chemoattractant. Eighteen patients with RA and four patients with osteoarthritis (OA) were used in this study. Thiobenzylester substrate, Succ-Phe-Leu-Phe-S-Bzl, was used to measure the activity of cathepsin G in synovial fluids. Monocyte migration induced by cathepsin G and synovial fluids was assessed by a 48-well microchemotaxis chamber technique. Immunohistochemical staining was performed to determine the cellular origin of cathepsin G in RA synovial tissue. A very low activity of cathepsin G was detected in synovial fluids from patients with OA. On the other hand, significantly increased activity of cathepsin G was detected in patients with RA when compared with the value of OA patients. A considerable monocyte chemotactic activity was detected in the synovial fluid of RA patients, and the activity was partially decreased by the treatment with inhibitors for cathepsin G, alpha1-antichymotrypsin and phenylmethylsulfonyl fluoride. The activity of cathepsin G was significantly correlated with the neutrophil counts in synovial fluids and the concentration of interleukin-6. Immunohistochemical studies showed that cathepsin G was strongly expressed by synovial lining cells, and weakly expressed by macrophages and neutrophils in synovial tissues. This study indicates that the monocyte chemotactic activity of cathepsin G may have a role in the pathogenesis of RA synovial inflammation.

In this study, we examined the content of antineutrophil cytoplasmic antibodies (ANCA) against defensins and cathepsin G in sera from systemic lupus erythematosus (SLE) patients and their significance in estimating the activity of SLE. Defensins- and cathepsin G-ANCA in sera from 28 patients with SLE, eight patients with rheumatoid arthritis (RA) and eight patients with microscopic polyangitis (mPA) were measured by ELISA. Significantly increased defensins- and cathepsin G-ANCA were found in sera of patients with SLE and mPA when compared with the value of normal controls. Though significantly higher defensins- and cathepsin G-ANCA were detected in both active and inactive SLE patients, the value in active SLE patients was significantly higher than inactive SLE patients. After the therapy with high dose of prednisolone, the serum level of defensins- and cathepsin G-ANCA was decreased, and this decrease was sustained for at least 16 weeks. This study suggests that defensins- and cathepsin G-ANCA may serve as useful markers of the disease activity of SLE.