The Significance of the Mast Cell in Rheumatic Disease

Rheumatoid arthritis (RA) is one of the most typical rheumatic diseases, and is characterized by chronic inflammation, cartilage destruction and joint deformity ［1,2］. During this process, profound hypertrophic changes of the synovium with infiltration of immune cells, increased vascularity, and hyperplasia result in the formation of a synovial pannus that invades cartilage and bone ［3］. In early stages of RA, the synovial membrane begins to invade the cartilage. In established RA, the synovial membrane becomes transformed into inflammatory tissue, the pannus (Fig. 1). The cell types that occupy cartilage-pannus junctions include synovial macrophages, fibroblasts, mast cells, polymorphonuclear lymphocytes (PMNs), and displaced, probably differentiated condrocytes ［4-6］. Recent studies of rheumatoid synovial tissue have demonstrated localized accumulations of mast cells and evidence of their activation/degranulation［7］.