B lymphocytes and humoral immune responses in rheumatoid arthritis.

Although the etiology of rheumatoid arthritis (RA) remains unknown at present, major evidence implicates humoral immune mechanisms in the pathophysiology of this disease. The primary lesions occur in the synovium and are characterized by immunological activation and chronic inflammation. Activated B cells and plasma cells secrete antibodies including rheumatoid factors and anticollagen antibodies. These antibodies give rise to immune complex formation and activation of the inflammatory cascade. There is no evidence that rheumatoid factor secreting B cells act as antigen presenting cells and present immune complex to T cells, leading to perpetuation of the inflammatory response.