Peri-articular lymphatic system and "Bi" theory of Chinese medicine in the pathogenesis and treatment of arthritis.

Rheumatoid arthritis (RA) and osteoarthritis (OA) are the two most common joint diseases, and they have characterization of synovial inflammation and cartilage destruction, associated with the accumulation of numerous catabolic mediators and inflammatory cells in the synovial space and surrounding soft tissues. How these factors are cleared and if the "clearance" process contributes to pathogenesis of arthritis are not known. Recently, we found the existence of the peri-articular lymphatic system in mouse joints. The blockade of lymphangiogenesis and lymphatic draining function accelerates while stimulation of lymphatic function attenuates the severity of joint tissue lesions in mouse models of RA and OA. More importantly, we noticed the similarity between the dysfunction of lymphatic drainage in arthritic joints and "Bi" theory of Chinese medicine (CM), and demonstrated that several Bi disease-treated herbal drugs directly affect the function of lymphatic endothelial cells. Here we review the advances about the interactions between joint inflammation and changes in the peri-articular lymphatic system and discuss our view of linking "Bi" theory of CM to lymphatic dysfunction in arthritis.