Rheumatoid arthritis (RA) is characterized by an invasive and tissue destructive infiltrate of lymphocytes, macrophages, and synoviocytes formed in the joints. Its etiopathogenesis and the role of the particular morphological components of synovitis remain unclear. There is evidence that its histological heterogeneity is correlated with synovium cytokine transcription. We investigated whether the serum cytokine profile is associated with the morphological appearance of the disease.
Tissue and serum samples were collected from 25 patients with clinically active RA and 25 with osteoarthritis (OA) as a control group. After histological analysis RA synovial biopsies were divided into 2 distinct types; 16 samples were characterized by diffuse lymphocyte infiltrates with no additional microanatomical organization. Lymphocytic aggregates with germinal center-like structures were found in 9 specimens. Serum concentrations of interferon-gamma (IFN-gamma), interleukin 12 (IL-12, p70 heterodimer), tumor necrosis factor-alpha (TNF-alpha), and IL-15 were measured by ELISA.
Low concentrations of IFN-gamma (p < 0.01) and IL-12 (NS) were found in RA patients' serum compared with OA controls. RA patients with follicular synovitis had lower serum concentration of IFN-gamma (p < 0.05) and IL-12 (p < 0.05) than patients with diffuse infiltrates. High concentration of TNF-alpha and IL-15 characterized RA patient serum in comparison with controls (respectively, p < 0.001 and p < 0.01). In the serum of RA patients with follicular synovitis TNF-alpha was a dominant cytokine (p < 0.01) compared to patients with diffuse disease. At TNF-alpha level > or = 44 pg/ml, 5 (56%) of 9 patients with follicular RA had such elevated values vs one of 16 diffuse patients (< 10%; p < 0.02). Only serum concentrations of TNF-alpha could effectively differentiate between patients with OA and subgroups of RA. Analysis of clinical data suggested that activity of rheumatoid disease in patients with follicular synovitis was more severe than in those with diffuse infiltrates.
The association between distinct histological appearance of rheumatoid synovitis and serum cytokine profile and diverse clinical activity of disease seems to confirm its heterogeneity.