Histologic studies on human synovial membrane. I. Metachromatic staining and the effects of streptococcal hyaluronidase

THE UPTAKE OF IRON IN RABBIT SYNOVIAL TISSUE FOLLOWING INTRA-ARTICULAR INJECTION OF IRON DEXTRAN. A LIGHT AND ELECTRON MICROSCOPE STUDY

Iron dextran (molecular weight 7,000) diffuses rapidly from the joint cavity through the synovium, along lymphatics and extracellular tissue spaces; articular cartilage is impermeable to iron dextran. There is also rapid cellular uptake by synovial lining cells, particularly of the vacuolar type; endoplasmic reticulum-containing lining cells rarely take up iron dextran. Cellular uptake is probably effected by pseudopodial folds projecting from the cell surface and enclosing extracellular material. Cells containing iron may degenerate and be ingested by phagocytes, and this may account for the concentration of iron in a smaller proportion of cells on or below the synovial surface in the later stages. At 6 to 18 hours after injection there is a mild inflammatory reaction and some synovial proliferation; from this stage onwards intracellular iron occurs in the form of haemosiderin. Granules of haemosiderin are present in the synovium 3 months after injection and possibly longer.

Microfibrillar elements in the synovial joint: presence of type VI collagen and fibrillin-containing microfibrils

OBJECTIVES

The aims were to isolate and positively identify the microfibrillar elements which have been observed in the synovial lining. In addition, synovial fluid was examined for these elements to improve the understanding of the role of these structures in health and disease.

METHODS

Bacterial collagenase digestion of bovine synovial linings and human and bovine synovial fluids was used to release intact, non-denatured microfibrillar elements. The microfibrils were isolated by Sepharose CL-2B chromatography and viewed by rotary shadowing. They were characterised by immunogold labelling with specific antibodies.

RESULTS

Intact type VI collagen microfibrils and fibrillin-containing microfibrils were isolated and positively identified in the synovial lining from bovine ankle joints by immunogold labelling. Type VI collagen microfibrils were also present in the synovial fluid.

CONCLUSIONS

The role of the microfibrillar elements in vivo is not fully understood, but their distribution in the synovial lining suggests they have an important role in the mechanical and physical properties of this tissue. The presence of type VI collagen microfibrils in synovial fluid poses the intriguing possibility that it may represent a product of microfibril turnover and a potential early marker for rheumatoid arthritis. Alternatively, type VI collagen may be specifically secreted into the synovial fluid to interact with hyaluronan and form part of the structure of synovial fluid.

Microfibrillar meshwork of the synovial lining and associated broad banded collagen: a clue to identity

The surface layer of synovial interstitium lining the rabbit knee was studied by transmission electron microscopy. Over a distance of 2-3 microns normal to the surface the interstitium contained a network of fine microfibrils (diameter 9.3 (0.7) nm, mean (SEM] which was quite dense in places (fractional area of projection 0.189 (0.023], and stained with ruthenium red. Periodic collagen fibrils were relatively scanty and fine (diameter 32 (2) nm) in this surface layer. Broad cross-striated bundles occurred in association with the microfibrils and B cells. These fibrous long spacing bundles (FLS) had a single period of 92.8 (2.8) nm with a broad dark band (37.6) (1.8) nm--so called 'zebra collagen'. Both the periodicity of the FLS and the morphological characteristics of the microfibrils are typical of type VI collagen, a widespread constituent of soft connective tissues. The functional importance of the inner microfibril network is likely to be mechanical, biochemical (glycosaminoglycan and glycoprotein entrapment), and to a very minor degree hydraulic resistance.

Cellular origin of hyaluronateprotein in human synovial membrane

Bright fluorescent staining, which indicates the presence of hyaluronateprotein, was observed in the lining cells of the synovial membrane following application of rabbit antiserum to hyaluronateprotein and a fluorescein-labeled antiserum to rabbit gamma-globulin. Staining was shown to be specific and due to antigenic determinants on or closely associated with the protein moiety of hyaluronateprotein.

Culture of synovial cells in vitro. Notes on isolation and propagation

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