Synovial tissue macrophages and joint erosion in rheumatoid arthritis.

To analyse the mononuclear cell populations in synovial membrane biopsies obtained before treatment from patients with rheumatoid arthritis (RA) and to correlate the findings with the degree of joint damage occurring over one year. Multiple needle biopsy specimens were obtained from inflamed knee joints on entry to the study. The tissue samples were examined using immunohistochemical techniques. The degree of joint damage was estimated using the Larsen radiological index. Twelve patients were studied. It was observed that there was a significant correlation between the number of synovial tissue macrophages and the degree of joint erosion over one year (r = 0.66; p = 0.04). The synovial lining layer contained large numbers of macrophages and the cellularity of the lining layer correlated significantly with the number of macrophages infiltrating the sublining areas (r = 0.65; p = 0.01). Finally, the cellularity of the lining layer correlated with the synovial fluid levels of interleukin-6 (r = 0.66; p = 0.04). The radiological course did not correlate with infiltrating T or B lymphocyte populations, but did correlate with other previously identified indicators of the clinical course, including a high index of disease activity and IgA rheumatoid factors levels. This study suggests that synovial tissue macrophages play a critical role in the pathogenesis of joint erosion in RA.