THE ANATOMY OF THE RHEUMATOID LESION

Rheumatoid arthritis primarily involves the synovial membrane of the j oints, together with that of the tendon sheaths and bursae. These stru ctures are targeted in a selective and symmetrical manner. The inflamm atory cell infiltrate is usually dominated by mononuclear phagocytes. These are recruited into the synovial lining as type A synoviocytes. A proportion of the mononuclear cell population has proven to be specia lized antigen-presenting accessory cells. The T and B lymphocyte infil trate is quite variable in intensity, but may become highly organized. Polymorphonuclear leukocytes pass rapidly into the joint space. The c ellular characteristics of rheumatoid nodules have some similarities w ith those of the synovial membrane. In a minority of patients, immunog lobulin production and circulating immune complex formation reaches le vels which precipitate the appearance of a complement mediated vasculi tis. This may lead to tissue damage in remote organs.