The microvasculature of the synovial membrane of the monkey: Ultrastructural studies

The normal synovial microvasculature of Cebus albifrons monkeys is characterized by fenestrated superficial capillaries and venules, and deeper vessels with thicker, active-appearing endothelium from which intravenously injected tracers occasionally were seen to have leaked. Carbon tracer was also identified in endothelial phagosomes. The possible roles of these vessels in joint inflammation is discussed. Leakage of still unidentified pathogenic agents from synovial vessels may be an early event in joint inflammation.