Synovium: what's new?

Better understanding of how it is affected by disease Until recently, the understanding of normal synovium was based solely on microanatomical studies and ideas about function based on classic observations on synovial fluid—but few experiments. We can now discuss the biology of the tissue in terms of the ontogeny of cells, morphogenesis, cell metabolism, the expression of cell surface ligands, matrix composition, and vascular and fluid physiology.1 A recurring theme is the interaction between cells and their matrix through adhesion systems that seem to modulate both cell behaviour and fluid flux. Having begun to understand how the tissue works, we can now construct models of how it becomes diseased. Synovium carries a specialised surface layer of intimal cells,2 which …