LAMELLAR BODY SECRETION - ULTRASTRUCTURAL ANALYSIS OF AN UNEXPLORED FUNCTION OF SYNOVIOCYTES

The intra- and extracellular distribution and relative density of lame llar bodies (LBs) were determined by electron microscopy in synovial b iopsies from 20 non-rheumatoid arthritis (RA) patients. LBs were found on the synovial surface, in intimal cells, throughout intimal matrix, in blood vessel walls, in endothelial cytoplasm and within vascular l umena. Lamellar profiles were observed in type B synoviocytes within r ough endoplasmic reticulum (RER), in association with the Golgi appara tus, and embedded in electron dense matrix (projection cores) in multi vesicular bodies. Exocytotic release of mature LBs into intimal matrix was observed. In type A synoviocytes the outer lamellae of LBs were f requently found in contiguity with the limiting membrane of lysosomes. An in vitro investigation of the ultrastructural features of LB forma tion in cultured type B synoviocytes (from 3 non-RA patients) gave res ults similar to those obtained in biopsies. These studies provide ultr astructural evidence of synoviocyte activity in secreting and degradin g phospholipid lubricant in a sophisticated system whose function and pathological derangements are largely unknown.