Synovial Fluid as a Crucial Component of the Joint Microenvironment in Rheumatoid Arthritis.

Rheumatoid arthritis (RA) is a systemic autoimmune disease closely associated with synovial tissue proliferation, pannus formation in small joints such as the hands, wrists, and feet, cartilage destruction, and systemic complications such as pulmonary, cardiovascular, neurological, and skeletal muscle lesions, glucocorticoid-induced osteoporosis and infections. The importance of confirming the diagnosis and determining local activity is given to the study of synovial fluid. A deep understanding of the pathological process in the joint in RA, characterized by changes in autoreactive CD4+ T cells, B cells, macrophages, inflammatory cytokines, chemokines, and autoantibodies, has now been achieved, although much remains to be explored. This article provides an updated overview of the pathogenesis of RA, revealing even more therapeutic targets for the intra-articular pathological process.