In the RA synovium, thcrc are many leukocytes adjacent to blood vessels. The exuberant proliferation of new blood vessels is crucial to the development of the RA pannus. Without new blood vessel growth, leukocyte ingrecs could not occur. Until recently, the endothelium lining the blood vessels was thought to be a passive bystander in inflammatory processes such as KA. Howcvcr, it is now recognized as playing an active and pivotal part in a variety of inflammatory and immunologic processes, including presentation of antigen to other immune cells, coagulation, cytokinc production, angiogenesis. recruitment of leukocytes to an inflainmatory focus, and ccllular adhesion (1)(Figure 1).