Electron Microscopy of the Human Synovial Membrane

Abstract

The structure of the lining cclls at the surface of the synovial membrane facing the joint cavity has been studied by elcctron microscopy. The long cytoplasmic processes of these cells appear to be oriented toward the surface of the membrane, where they overlap and intertwine. The matrix of the lining cells contains dense material but no fibers with thc periodicity of collagen. The lining cells are divided into two cell types or states of activity on the basis of their cytoplasmic contcnts. Type A is more numerous and contains a prominent Golgi apparatus, numerous vacuolcs (0.4 to 1.5 microns in diamctcr) containing varying amounts of a dense granular material, many filopodia, mitochondria, intracellular fibrils, and micropinocytotic-likc vesicles. Type B contains large amounts of ergastoplasm with fewer large vacuoles, micropinocytotic-like vesicles, and mitochondria. The probable functions of these cells are discussed in the light of current knowledge of the metabolism and function of the synovial membrane.

Electron microscopic study of HLA‐DR and monocyte/macrophage staining cells in the rheumatoid synovial membrane

“…In the present study, EM revealed 3 different patterns of DR staining in the lining area of RA synovium. Strongly DR+ lining cells were identified as the type A, or macrophage-type, cells described by Barland et a1 (28), and largely DR-cells were identified as the type B, or fibroblast-type, cells. Intermediately staining DR+ cells of a type previously described as type I1 (37) or type C cells (38,39) were also observed.…”

“…The strongly DR+ cells had numerous irregular cytoplasmic processes, many lysosomes, vacuoles, and filopodia, indicating that these cells were of the macrophage lineage and, therefore, were type A lining cells (28,29). Type B lining cells, which had a round shape, eccentric nucleus, well-developed rough endoplasmic reticulum, and Golgi apparatus, were either negatively stained or showed very weak DR staining ( Figures 3A and B).…”

“…Hardened sections were detached Figure 1 illustrates the types of areas observed in the RA synovial membrane, i.e., lining layer, lymphocyte-rich area, transitional area, plasma cell-rich area (not shown), and interstitial area. The lining area has several layers of proliferating cells, mainly type A and type B synovial lining cells (28,29). Lymphocyterich areas, which consist mostly of densely packed small lymphocytes, usually more than 90% of the total cell ~oopulation (30,3 l ) , contain predominantly OKT4+ helperhnducer cells (23).…”

Expression of estrogen receptor α (ERα) in the rat temporomandibular joint

“…The lining layer of the synovial membrane contains two kinds of lining cells: macrophage-like type A and fibroblastic type B cells (Barland et al, 1962;Graabaek, 1984). We were unable to observe all organellae in the ER␣-positive cells due to the use of GMA resin, which is disadvantageous for detailed observations.…”

“…Many ultrastructural investigations have pointed out that the synovial membrane consists of two kinds of synovial lining cells: macrophage-like type A and fibroblastic type B cells (Barland et al, 1962;Graabaek, 1984). In rodents, type A cells are characterized by numerous vesicles, vacuoles, and lysosomes, while type B cells possess a well-developed rough endoplasmic reticulum and a number of dense secretory granules.…”