Dynamic expression of transforming growth factor-betas (TGF-beta) and their type I and type II receptors in the synovial tissue of arthritic rats.

A well characterized animal model that shares many characteristic features with rheumatoid arthritis (RA) is collagen-induced arthritis (CIA) in DA rats. Recent studies have demonstrated that TGF-beta, a multifunctional cytokine, is an important modulator of the immune response in CIA, and possibly also in RA. In this study we have investigated the expression of the precursor forms of TGF-beta1, TGF-beta2, TGF-beta3, as well as TGF-beta type I receptor (TGF-betaRI) and TGF-beta type II receptor (TGF-betaRII) in the synovial tissue of arthritic rats during the course of the disease. By using immunohistochemical techniques, an abundant expression of all three TGF-beta isoforms and their receptors was observed in the arthritic synovia, an expression that increased with time after onset of disease. Antibodies to TGF-beta1, TGF-beta2, TGF-betaRI and TGF-betaRII stained blood vessels intensively, already at the early onset of inflammation, whereas the synovial lining layer and chondrocytes expressed strong immunoreactivity later on in the inflammatory process. The most intense staining with these antibodies was detected in fibroblasts within fibrotic tissue, in particular at the cartilage pannus junction. Interestingly, TGF-beta3 only stained macrophage-like cells and chondrocytes in the synovia. The data suggest that the abundant expression of TGF-beta1, TGF-beta2, TGF-beta3 as well as TGF-betaRI and TGF-betaRII in the synovia, is of pathogenic importance in the development of CIA, although the question of how the different TGF-beta isoforms may enhance or counteract different arthritogenic events remains open.