Comparison of the features of arthroscopic synovial biopsies with biopsy samples obtained at surgery

Objective

Most of the older descriptions of the synovial infiltrate are based on examination of synovial tissue (ST) obtained at surgery. However, ST from end-stage destructive rheumatoid arthritis (RA) and arthroscopic biopsies obtained during active inflammation could exhibit different characteristics. The aim of this study was to define the cell infiltrate, the expression of proinflammatory cytokines, angiogenic factors, and matrix metalloproteinases in ST selected at arthroscopy compared with ST from end-stage RA obtained at joint replacement.

Methods

Synovial biopsy specimens were obtained from the actively inflamed knee joints of 11RA patients with longstanding RA by arthroscopy and compared with ST from 13 patients with end stage, destructive RA requiring joint surgery. Use of medication was on average similar in the 2 groups. Immunohistologic analysis was performed using monoclonal antibodies (mAb) to detect T cells, plasma cells, macrophages, fibroblast-like synoviocytes (FLS), as well as the expression of IL-1β, IL-6, and TNF-α, matrix metalloproteinase (MMP)-1, MMP-3, MMP-13, tissue inhibitor of matrixmetalloproteinase (TIMP)-1, and vascular endothelial growth factor (VEGF). The integrated optical density was evaluated by computer-assisted image analysis.

Results

The expression of CD68+ macrophages was significantly higher in ST selected at arthroscopy compared to samples obtained at surgery, both in the intimal lining layer and in the sublining layer. The expression of CD3+ T cells also tended to be higher in arthroscopic samples. There was no clear difference in the expression of CD38⁺ plasma cells and CD55⁺ FLS. The expression for TNF-α, IL-6, MMP-1, MMP-3, MMP-13, TIMP-1, and VEGF was on average higher in ST obtained at arthroscopy. The expression of IL-1β was on average higher in ST obtained at surgery.

Conclusion

Active arthritis activity is especially associated with increased cell infiltration, expression of proinflammatory cytokines, MMPs, and angiogenic growth factors in synovial biopsy samples selected at arthroscopy. Increased expression of IL-1β in the synovium of patients with destructive RA requiring joint replacement may well reflect the important role of IL-1β in cartilage and bone destruction.