Circulating activated lymphocytes in rheumatoid arthritis: a marker of synovial inflammation.

Peripheral blood lymphocytes have been studied in rheumatoid arthritis using a Ficoll density gradient in which activated cells separate as low density lymphocytes (LDL). Increased numbers of LDL are found in rheumatoid patients with active synovitis but not in those with active extraarticular disease such as vasculitis in the absence of active synovitis. The association of activated cells with synovitis is confirmed by serial studies during cyclophosphamide therapy in which LDL correlate with a computerized thermographic index of joint inflammation. The separate immunological markers of vasculitis and synovitis, and the possible role of LDL in the pathogenesis of the latter, are discussed.