Rheumatoid synovitis is characterized by an invasive and tissue-destructive infiltrate of lymphocytes, macrophages and synoviocytes. Matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) produced by these cells are important in the remodelling of the articular tissues in rheumatoid arthritis (RA). The aim of this study was to explore whether the serum concentrations of MMPs and their inhibitors were correlated with the histological appearance of the disease.
Tissue and serum samples were obtained from 37 patients with clinically active RA and 30 with osteoarthritis (OA). Morphological analysis allowed the division of RA synovial specimens into two distinct types. In 22 samples only diffuse infiltrates of mononuclear cells without further microanatomical organization were found. In 15 specimens we observed lymphocytic conglomerates with germinal centre-like structures. Serum concentrations of interstitial collagenase (MMP-1), stromelysin-1 (MMP-3), gelatinase B (MMP-9), TIMP-1 and TIMP-2 were measured with an ELISA technique.
Unique serum profiles of MMPs and TIMPs were identified in each of the two histological types of RA synovitis. The serum concentrations of MMP-1, MMP-3 and MMP-9 were higher in RA patients than in OA patients used as a control group (P<0.001 for all comparisons). These three MMPs dominated in the serum of RA patients with follicular synovitis compared with those with diffuse synovitis (P<0.05, P<0.01 and P<0.001 respectively). The analysis of the serum concentrations of TIMP-1 and TIMP-2 showed that their levels were also elevated in RA patients compared with OA patients (P<0.001 and P<0.01 respectively). Only TIMP-1 was found in a significantly higher concentration in the serum of RA patients with follicular synovitis than in those with diffuse synovitis (P<0.05). The serum concentrations of MMPs and TIMP-1 clearly identified patients with two different histological types of rheumatoid synovitis and with OA. Additionally, the analysis of clinical data showed that the rheumatoid disease in patients with follicular synovitis seemed to be more active than in those with diffuse synovitis.
The morphological appearance of rheumatoid synovitis and the serum MMP and TIMP-1 profile were correlated with the clinical activity of the disease, confirming the heterogeneity of RA. These associations also suggest that patients with different histological forms of RA might require different treatment regimens.