The effect of synovial tissue on the breakdown of articular cartilage in organ culture

Living (pig) cartilage in contact with synovium lost both proteoglycan and collagen and sometimes became reduced to a mass of fibroblast-like chondrocytes without matrix; dead cartilage lost proteoglycan but less collagen. Similar changes appeared in living cartilage grown at a distance from the synovium but in the same dish; dead cartilage was unaffected.

CONCLUSION

the synovium has a) a direct, presumably enzymatic action on cartilage matrix and b) an indirect effect mediated through the chondrocytes.

Morphological evidence of a polypeptide-like secretory function of the B cells in the mouse synovial membrane

In the synovial membrane of the mouse, morphological features associated with active secretion are unusually well developed in cells immediately subjacent to the lining layer (in the position of B cells), comparable to those of cells known to elaborate polypeptides.

[Human joint capsule in osteoarthrosis (morpholocical changes) (author's transl)]

Morphological investigations of the joint capsules in osteoarthrotic-changed joints have given rise to doubts about the present theory of the causal aetiology of the osteoarthrosis. In every inspected and demonstrated illustration beside the partly normal capsules segments could be found every transition between mild regressive alterations and most massive proliferative changes of the conective tissue and the lining cell layer. It was extraordinary, that the strongly dilated vessels were filled with red blood cells. In another part of the same case was found a massive stricture caused by concentrically deposited substances, which were impregnated with collagenous fibers. Regeneration of the vessels frequently happened adjacent totally obstructed ones. Round-cell infiltrations, granulocytes or other indications of an inflammatory synovitis are found only in a few cases. The intracartilaginous enzymatic reactions, which have been much talked of and which were explained as characteristic of the osteoarthrosis cannot be the cause of the degradation of the cartilage, particularly, because of the normal cell count which is to be found in the synovial fluid. We can answer this problem, if we can prove that the substrates of the chondral metabolism themselves exert a direct or indirect influence on the interstitial connective tissue with induction of the powerful proliferation of the same tissue. The changes in the transit zone would be secondary and their effect on the lining cell layer would increase the progression of the arthrotic events.

Ultrastructural study of avian synovium infected with an arthrotropic reovirus

Three-week-old chicks were inoculated via the foot pad with the avian reovirus (strain WVU 2937) that has been proved to be the causative agent in avian viral arthritis. The initial stages of the avian reovirus infection in the synovium of the hock joint were studied by transmission electron microscopy to shed light on the early virus-host relationship of an arthrotropic virus and synovial tissue. At 48 hours postinoculation (PI), coated, partially coated, and uncoated virus particles were seen in a dense lysosome-like inclusion in the cytoplasm of subsynovial fibroblasts. Virus replication was demonstrated in fibroblasts of the subsynovium 4 days PI. Infiltration of leukocytes into the area of the virus replication was noted at the time of virus replication (4 days PI). By the second week of the infection (11 days PI), the subsynovium was heavily infiltrated with lymphocytes and plasma cells, and proliferative changes had occurred in the synovial lining cells.

[Identification of the crystals observed in the destructive arthropathies of chondrocalcinosis]

Study of the synovial membrane and cartilage demonstrating two destructive arthropathies of the knee diagnosed in subjects with articular pseudogout. Scanning electron microscopy reveals the presence of many crystals on the surface of the cartilage and the synovium and in the depth of the cartilage. These can be grouped into two families on the basis of dimensions and morphology. The first consists of those shaped like arrowheads and are large (80-100 microns long.) They were formally identified using Weissenberg's technique; dihydrated calcium hydrogenophosphate (CaHPO4.2H2O) is involved here. In the second family the crystallogenesis is different (prism or lozange-shaped) and the crystals themselves have not been identified with certainty because of their tiny size (20 microns). The hypothesis is proposed that the crystals of dihydrated calcium hydrogenophosphate properly belong to the destructive arthropathies of pseudogout; while not necessarily its cause, they may help explain its development.

Light and electron microscopy study of capillaries in normal and inflammatory human synovial membrane

Synovium aspirated from the knee joint by trochar was studied by light and electron microscopy in 40 cases of inflammatory arthritis and in 10 controls. The morphology of synovial capillaries, extravascular plasma diffusion, interendothelial vascular gaps, extracapillary blood cell migration, vascular congestion, endothelial hyperplasia, and obliteration of the capillary lumen by endothelial cells were compared in normal and inflammatory synovia. Inflammatory synovitis was characterised by the number and diversity of blood cells migrating through the interendothelial pathway out of the capillary lumen. Polymorphonuclear leucocytes were the blood cells most often seen at interendothelial junctions. No other capillary changes that might be related to synovial inflammation were found.

Localization of gold in synovial membrane of rheumatoid arthritis treated with sodium aurothiomalate. Studies by electron microscope and electron probe x-ray microanalysis

The localization of gold in the synovial membrane of rheumatoid arthritis patients treated with sodium aurothiomalate was examined and quantitative analysis of epon-embedded sections was carried out with a wavelength dispersive x-ray microanalyser. Gold was only detected in the lysosomes of synovial lining type A cells and subsynovial mononuclear cells in the form of filamentous deposits and highly electron-dense granules, the latter being few in number. The concentration of gold within the lysosomes containing the characteristic deposits and granules was equivalent to that in epon-embedded standard specimens of freeze-dried albumin in which 2-0-87-4 mg/ml of gold was included. In addition, sulphur was detected in the lysosomes containing the filamentous deposits, but the S/Au x-ray signal ratio was not equal to that detected in sodium aurothiomalate. The significance of the coexistence of gold with sulphur in lysosomes is discussed.

Scanning electron microscopy of equine synovial membrane

The scanning electron microscopy of synovial membrane from the radiocarpal and intercarpal joints near the lateral and medial borders of the tendon of the extensor carpi radialis muscle was studied in 5 ponies. Three different morphologic types of synovial membrane were observed. Type 1 synovial membrane was folded and had a surface mat of fibers separated by 1- to 5-micron-diameter holes. The 2nd and 3rd types of synovial membrane were both villous. The surface of type 2 synovial membrane was fibrillar but the surface of type 3 synovial membrane was cellular. The type of synovial membrane present was related to the function of the joint capsule region rather than to the type of subintimal connective tissue. Normal equine synovial membrane was found to be more villous in some regions of the joint capsule than synovial membrane of other species.

The pig synovium, II. Some properties of isolated intimal cells

I. The effect of trypsinization. Certain physiological and immunological properties of isolated intimal synoviocytes were studied in various in vitro systems. Suspensions of the synoviocytes were obtained by incubating sheets of joint capsule in a solution of trypsin and then scraping off the intimal cells with a small knife. Synovium was examined immediately after trypsinization, but before scraping, by light and electron microscopy. The intimal cells had withdrawn many of their long processes, acquired lamelliform pseudopodia, and somewhat resembled cells of the A-type (Barland et al. 1962). To test the viability of the trypsinized synovium, fragments of trypsinized joint capsule were explanted in organ culture with the intima in contact with a Millipore substrate (Fell et al. 1976). After two days the intimal synoviocytes had become branched and, as in untreated control explants, now resembled B-cells. II. Phagocytosis and opsonic adherence. In a freshly prepared suspension of synoviocytes scraped from trypsinized synovial tissue many cells were still branched, but during 1 1/4 hours' incubation in serum-containing medium the majority had withdrawn their processes and become rounded. Cells in the branched form had little capacity for phagocytosis, but most of those in the rounded form were actively phagocytic. After suspensions of intimal cells had been incubated with opsonized sheep erythrocytes, most of the rounded, but none of the few remaining branched cells, had formed rosettes. Intimal cells from scraped synovial tissue were maintained in Sykes-Moore chambers for periods of up to 48 hours. Although the young pig synovium contains only a small proportion of macrophage-like (A-type) cells, in the cultures the cell population consisted of cells indistinguishable from macrophages, with a few small colonies of typical fibroblasts. In marked contrast to the fibroblasts, the macrophage-like cells in the Sykes-Moore cultures were highly phagocytic and formed conspicuous opsonic rosettes. Excessive phagocytosis inhibited subsequent rosetting by the macrophage-like cells. III. The effect of antiserum, with and without complement, on synovial cells. In view of earlier work by Fell & Barratt (1973) the effect of rabbit antiserum to pig erythrocytes (AS) with and without serum complement (C') on intimal synoviocytes in a Sykes-Moore chamber was investigated. AS+C' either lysed the macrophage-like cells or caused them to fuse into multinucleate giant cells. In the presence of AS without C', the macrophage-like cells formed large lakes of multinucleated cytoplasm. Fibroblasts in the same cultures were much more resistant to lysis by AS+C' and did not form multinucleate giant cells when exposed to AS either with or without C'.

Epithelioid sarcoma: ultrastructural similarity to nodular synovitis

The ultrastructure of nodular synovitis of the knee and epithelioid sarcoma of the hand are compared. Both lesions show a similar pattern of light and dark cells having filopodia and microvilli, an outer coat of finely granular matrix without well defined basal laminae, maculae adherentes and attachment sites, pinocytotic vesicles, cytoplasmic filaments and complex nuclear invaginations. These similarities suggest a common histogenesis and support the concept that the epithelioid sarcoma is derived from synovioblastic mesenchyme.

Cell proliferation in rheumatoid synovial tissue

Rheumatoid synovial tissue cell proliferation was studied by incubating fresh synovial tissue samples with [3H]-thymidine in vitro. The samples were collected at operation from 7 rheumatoid patients. It was found that 0.9-4.9% of the total cell population, excluding the synovial lining cells, became labelled.

Experimental restoration of the digital synovial sheath

The digital synovial sheath constitutes an important component of the delicate mechanism of flexor tendon nutrition and gliding function, In the present study the true nature of the inner cell layers of secondary healed defects in the tendon sheath as well as of free tendon sheath autografts were studied. Leghorn chickens were used as experimental animals and the gradual development of the pseudosheath as well as the healing of sheath autografts were studied both macroscopically and histologically including transmission electron miscroscopy. Synovial regeneration by extension from intact parts of the sheath was never observed and the pseudosheath formed around silastic rods consisted of granulation tissue with fibroblasts and macrophages. The free tendon sheath autografts demonstrated a normal process of healing at the edges of the defect. Synovial regeneration appeared to be that of metaplasia and proliferation of fibroblasts and macrophages. This phenomenon was demonstrable both in the secondary healed defects and more convincingly in the sheath autografts. Further, the silastic rod was found to induce foreign body reaction in the healing synovium. It is concluded that grafting of autologous tendon sheath tissue seems to be a promising method for restoration of defects in the digital tendon sheath.

The pig synovium. I. The intact synovium in vivo and in organ culture

1. The normal synovium of the metacarpophalangeal joints of young pigs was examined by light and electron microscopy with special reference to the superficial layer (intima). 2. Cells of the macrophage-like or A-type (Barland et al. 1962) constituted only a small proportion of the intimal synoviocytes; the majority were of the intermediate and B-types. 3. Synovial villi were explanted on Millipore filters and maintained as organ cultures. The intimal cells in contact with the Millipore formed long branched processes which penetrated deeply into the substrate; these cells, which had a very well-developed endoplasmic reticulum, resembled those of the B-type. The synoviocytes at the upper (free) surface of the villus withdrew their long processes, acquired lamelliform pseudopodia, and their endoplasmic reticulum regressed; they were similar in appearance to the A-type. 4. In the organ cultures the highly branched cells (B-type) next to the Millipore were less phagocytic than the rounded cells (A-type) at the free surface of the villus.

Ultrastructure of the haemophilic synovial membrane and electron-probe X-ray analysis of haemosiderin

An ultrastructural study of the haemophilic synovial membrane revealed the presence of solitary siderosomes, compound siderosomes and a peppering of the cell cytoplasm with electron-dense particles. These changes were found in synovial intimal cells, subsynovial macrophages and fibroblasts. Electron-probe X-ray analysis of siderosomes revealed the presence of iron and traces of phosphorus. On the basis of previous and present studies it is postulated that haemosiderin is essentially a condensate of hydrated ferric oxide and that a variable amount of phospholipid material lies in company with it in the siderosome.

Selective concentration and localization of gold in macrophages of synovial and other tissues during and after chrysotherapy in rheumatoid patients

Gold distribution was studied in the tissues of 7 rheumatoid patients who had died from 0 to 23 years after stopping chrysotherapy (sodium aurothiomalate) and in 23 samples of synovial tissue removed surgically at intervals during chrysotherapy in 5 patients. After the application of a highly specific staining technique, the cellular localization of gold was examined microscopically in various tissues: the amounts of gold in selected areas of the same specimens which had been examined microscopically were then measured by neutron activation analysis. During active chrysotherapy gold was abundant in synovial lining cells except where a fibrin layer was present on the surface; after stopping chrysotherapy, gold disappeared from the synovial lining cells. Gold accumulated progressively in the subsynovial connective tissues during chrysotherapy, but was not uniformly distributed, and bore no relationship to fluctuations in serum gold levels. Gold deposition was not confined to joint tissue, but was found within the macrophages of many organs, renal tubular epithelium, and, after recent chrysotherapy, in seminiferous tubules, hepatocytes, and adrenal cortical cells. Gold persisted in synovial and other tissues for up to 23 years after chrysotherapy was stopped. The overall findings indicated that gold is selectively concentrated within inflamed synovial tissues during chrysotherapy.

Electron probe x-ray analysis of siderosomes in the rabbit haemarthrotic synovial membrane

Electron probe x-ray analysis of siderosomes produced in the rabbit synovial membrane by repeated injections of autologous blood revealed two kinds of siderosomes; (1) those containing a small amount of phosphorus and, (2) those in which no phosphorus was detectable. On the basis of these findings and past studies it is concluded that haemosiderin is an inorganic compound of iron, probably a hydrated ferric oxide and that a variable amount of organic material (proteins, lipids, phospholipids, etc.,) probably occurs in company with the haemosiderin in the siderosome, but these variable components which decrease in amount with the passage of time cannot be considered as an integral part of haemosiderin.

Prostaglandin synthetase activity from human rheumatoid synovial microsomes. Effect of 'aspirin-like' drug therapy

Using a radiometric technique, prostaglandin synthetase activity was measured in vitro in the microsomal fraction of 19 synovial tissues taken from 17 rheumatoid arthritis patients. The enzyme was inhibited in vitro by low concentrations of several 'aspirin-like' drugs, though paracetamol and salicylic acid were virtually inactive. While the synthetase preparations from patients receiving indomethacin, ibuprofen, or naproxen therapy exhibited considerable activity in vitro, we were unable to show any activity in preparations from patients taking aspirin, even in low doses. These findings suggest that in vivo aspirin may be unique in being an irreversible inhibitor of the enzyme, compared with other 'aspirin-like' drugs.

Aurosome formation in articular tissues after parenteral administration of gold

Intramuscular injection of sodium aurothiomalate (Myochrysine) produced lysosomes (aurosomes) of a characteristic morphology distinct and different from other lysosomes. The aurosome is characterised by particle and granulestudded electron-dense membranous formations which present as rod-like and curled structures. Intramuscularly injected sodium aurothiomalate in immature rabbits leads to the production of aurosomes in the articular cartilage chondrocytes and synovial intimal cells and subsynovial macrophages. In mature rabbits aurosomes develop only in the synovial intimal cells and subsynovial macrophages, but not in the chondrocytes.

Microscopic comparison of the synovial changes in rheumatoid arthritis and ostroarthritis

Whereas the histopathologic picture of the synovial membrane in rheumatoid arthritis varies widely and that in osteoarthritis displays a small range of changes, light- and transmission electron microscopic studies of synovial sections from both disease entities complement each other and assist reciprocally to corroborate the observed changes. Beyond that comparative survey of the ascertained histopathologic features and their correlation with clinical observations disclose that a study of a larger material of specimens permits with some limitations to infer the nature of the joint disease.

Innervation of the synovial membrane of the cats joint capsule

Results of investigations on the occurrence of nerve fibres and endings in the synovial membrane of the knee and elbow joint in the cat are reported. The stratum synoviale contains only autonomic fibres, running in the adventitia of arteries. Free nerve endings are lacking in the stratum synoviale. Simple Pacinian corpuscles with an inner core are occasionally observed in the border zone between the stratum synoviale and fibrosum. The ultrastructure of these endorgans resembles that of Pacinian corpuscles in the hairless and hairy skin of the cat.

The origin and nature of pseudo-synovium appearing around implanted Silastic rods: an experimental study

The pseudo-synovium appearing around Silastic rods is a labile layer made up of a range of cells from undifferentiated fibroblast precursors through to mature fibrocytes. Various factors influencing their behaviour are discussed. The optimum time for grafting into a rod-induced sheath would seem to be in excess of four months.

Fine structural analysis of rabbit synovial cells. II. Fine structure and rosette-forming cells of explant and monolayer cultures

The fine structure and plasma membrane receptors of explant and monolayer cells of normal rabbit synovium were studied. In explants about 10% of the cells were round and formed rosettes with IgC and C3 markers, whereas the remaining cells were stellate, resembled young fibroblasts, and had no receptors for IgG and complement. Monolayer cells looked like fibroblasts, produced fine extracellular fibrils and hyaluronate, and formed no rosettes. Thus early cultures contain both macrophages and fibroblasts but only the latter persist in monolayer.

[Pigmented villonodular synovitits of the hip: ultrastructure and aspects on scanning electron microscopy]

The authors studied one case of pigmented, villonodular synovitis (PVNS) of the hip by means of optical microscopy and by transmission and scanning electron microscopy. Scanning electron microscopy showed that the surface of the PVNS is completely different from that of rheumatic synovitis, in particular that of rheumatoid synovitis. The composition and the cellular morphology of the outer layer of the PVNS appear, however, to be similar to those of normal synovial membrane of arthrosic synovial membrane. Clumps of red corpuscles, enclosed in a fibrin network, were visible on the surface of the PVNS in a way that the authors has never seen previously in the 19 other human synovial membranes, normal and pathological, they had studied in this way. The totality of the microscopic findings confirms the importance of the role played by the intra-articular and intra-synovial haemorrhages, and by the macrophage reactions that follow, in the development of the lesions that characterize PVNS.

[Needle biopsy in gout and pseudogout (author's transl)]

INTRODUCTION

Radiological and morphological findings in advanced arthritis urica and pyrophosphate arthropathy are well known. In contrast, the early changes of synovial membrane in these disturbances of metabolism pose diagnostic problems. With the assistance of various cytological techniques and polarizing microscopical as well as electron microscopical investigation it was examined to what extent needle biopsies can be helpful in the differential diagnosis of gout and pseudogout.

MATERIAL AND METHODS

In 8 patients with gout and 11 patients with pseudogout synovial fluid and small tissue specimens could be obtained with the aid of the Parker-Pearson needle. Both fluid and tissue specimens were investigated light and electron microscopically. Cell counts were evaluated in a Rosenthal chamber. The differentiation of the cells in stained smears was done by counting 200-600 cells per case. Crystals were identified by polarizing microscopy in wet preparations of freshly aspirated synovial fluid.

RESULTS

Polarizing microscopy of synovial fluid detected intra- as well as extracellular urate and pyrophosphate crystals. The wedge-shaped urate crystals and the larger partly polygonal pyrophosphate crystals showed different polarizing microscopical properties and a negative birefringence. The absolute cell counts in gout were higher than those in pseudogout. The relative cell counts of the different cell types in synovial fluid showed more variation in gout than in pseudogout. Cases with acute gout developed a relative leukocytosis in contrast to a relative lymphocytosis in chronic gout. A relative leukocytosis was constant in all patients with pseudogout. Sclerosed areas with scarce and plump villi as well as sometimes hyperplastic and polymorphous synovial cell layers could be demonstrated histologically in the tissue specimens of the needle biopsies in cases with gout. Urate crystals were less frequent in specimens fixed in formalin. The histological alterations in pseudogout were uniform, 2-4 rows of slightly pleomorphic synovial cells lined the inner surface of the joint capsule, sclerosing alterations were less frequent. Pyrophosphate crystals and calcified particles were seen within the synovial lining cells, the connective tissue and the enodthelial cells of the blood vessels in pseudogout specimens. Intra- as well as extracellular crystals could also be demonstrated with the aid of scanning electron microscopy in sediments of synovial fluid in gout and pseudogout. Transmission electron microscopical investigations of synovial tissue specimens detected proliferated and pleomorphic synovial lining cells in gout in contrast to a more monomorphic appearance of these cells in pseudogout. The crystals were washed out during the preparation techniques for transmission electron microscopy so that needle-like empty spaces resulted within cytoplasm of the phagocytic cells. These clefts were surrounded by phagosomal structures and densified cytoplasmic ground substance; sometimes they were also lined by membranes...

Attempts to identify viruses in rheumatoid synovial cells

Synovial fibroblast cell strains derived from the synovial membranes of 7 patients with rheumatoid arthritis were examined for the presence of viruses, in particular leucoviruses. Seven similar synovial strains derived from patients with other arthritic conditions were used as a control group. Evidence of the presence of a virus or a viral genome was looked for by several methods of induction followed by 3H-uridine labelling of the cultures. In addition, the culture supernatant, after induction and after the synovial strains had been co-cultivated with a variety of cell lines from several species, was assayed for the presence of viral RNA-dependent DNA polymerase activity. The DNA-polymerase activity of the synovial cells themselves was also determined. No evidence was found by any of these techniques to indicate the presence of virus or viral information within the synovial fibroblasts.

Nuclear fibrous lamina in the rheumatoid synovium

Biopsy specimens of synovial membrane were obtained from patients with rheumatoid arthritis and from patients with nonrheumatoid conditions. Comparison of the mean thickness of the lamina in the rheumatoid and nonrheumatoid groups showed a statistically significant thickening of the lamina in the rheumatoid group (rho less than .01). There was no statistically significant difference in the thickness of the lamina before and after chrysotherapy.

Electron microscopic autoradiography of 35SO4-labelled material closely associated with collagen fibrils in mammalian synovium and ear cartilage

Electron microscopic autoradiography of connective tissue obtained from mice and rabbits previously injected with 35SO4 indicated that sulphated proteoglycans are localized on collagen fibrils. Ruthenium Red-positive transverse belts surrounding fibrils near the a-bands were heavily labelled, but fine lateral filaments of Ruthenium Red-positive material were not. These filaments, which interconnect collagen fibrils in a variety of connective tissues may represent linear aggregations of hyaluronic acid, glycoproteins and non-sulphated or long-lived sulphated proteoglycans.

The arthropathy of hemochromatosis

Five cases of hemochromatosis arthropathy are presented and the distinctive radiological features of the disease are described. Although the condition is typically degenerative, showing subchondral cyst formation, sclerosis, and thinning of cartilage, its distribution is characteristic. Selective degenerative changes of the second and third metacarpophalangeal joints are striking, particularly in the hands, while abnormalities in the intercarpal joints are variable and the interphalangeal joints are spared. Chondrocalcinosis involving both fibrous and hyaline cartilage is frequently seen as well, particularly in the large joints. The calcification is due to deposition of calcium pyrophosphate crystals, perhaps resulting from iron inhibition of pyrophosphatase.

Evolution of aurosomes in rabbit synovial membrane

Intra-articular injection of sodium aurothiomalate (Myochrysine) into rabbit knee joints produced lysomes (aurosomes) of a characteristic morphology in synovial intimal cells and subsynovial macrophages. Such lysosomes are distinct and different from other lysosomes and those seen after injection of sodium thiomalate. A study of the morphological events that occur after injection of gold salt shows that at first the aurosome contains electrondense granules but later membranous formations (myelinoid membranes) presenting as rod-like and curled structures develop. With electron probe x-ray analysis, gold, phosphorus, and traces of calcium were detected in the aurosome.

Ultrastructural changes produced in rheumatoid synovial membrane by chrysotherapy

Biopsies of rheumatoid synovial membrane before and after chrysotherapy were examined with the light and electron microscopes, and subjected to electronprobe x-ray analysis. The main change noted was the occurrence of electron-dense deposits of characteristic morphology within pre-existing lysosomes. Such deposits were also seen in other varieties of lysosomal bodies. X-ray analysis showed the presence of gold, phosphorus, osmium, and calcium in these deposits. The present study shows that gold enters the pre-existing lysosomes, supporting the concept that the beneficial effects of chrysotherapy are due to its action on the lysosome.

Capillary lengths and areas, and intercapillary distances in tissue near the human knee

Quantiative stereological electron microscopy has been used to investigate the capillary lengths, surface areas and intercapillary distances in the tissues around the human knee, the synovial membrane, synovial capsule, fat and tendon. The vascularity of these regions was much less than in other areas of the body, especially muscle.

Ultrastructural studies of rabbit synovitis induced by autologous IgG fragments. II. Infiltrating cells in the sublining layer

The synovial sublining layer of rabbits with synovitis induced by intra-articular injection of cathepsin D digested autologous IgG fragments (Fab2) has been examined under the electron microscope. Twelve or more injections of autologous Fab2 led to chronic synovitis with dense mononuclear cell infiltrates containing lymphocytes, blastic cells, plasma cells and macrophages. In the infiltrates there was evidence that the lymphocytes had been activated prior to transformation into mature plasma cells. Indirect evidence suggests that T lymphocyte activation also occurred in these infiltrates. Cellular contacts between macrophages and lymphocytes or plasma cells as well as between M cells and lymphocytes were demonstrated. These contacts are tentatively interpreted as a feature of ongoing immune processes in the synovium.

Ultrastructural studies of rabbit synovitis induced by autologous IgG fragments. I. Proliferation of the lining cells

The synovial lining cells of rabbits with experimental synovitis induced by intra-articular injection of cathepsin D-digested autologous IgG fragments (Fab2) have been subjected to electronmicroscopic study. From 3 to 50 such injections resulted in hyperplasia of the lining layer with an increase in the numbers of phagocytic and synthetic cells. Morphologically the phagocytes were classified into monocyte-like cells, mature and immature phagocytes, and epitheloid=like cells, indicating that synovial M cells may originate from blood monocytes that differentiate in situ like the monocytes in other tissues. The finding of "undifferentiated" (mesenchymal), transitional and mature synthetic cells in the lining layer suggests that synovial F cells are derived from the undifferentiated mesenchymal cells persisting in the synovial membrane in postnatal life. In the animals with synovitis, the synthetic cells were found to undergo mitosis but not the phagocytic cells. It is concluded that the hyperplasia of the lining layer is due to two distinct processes, namely invasion by precursors of M cells (monocytes) and local proliferation of F cells. As far as immune reactions involved in the synovitis are concerned, the possible roles played by lysosomal substances in these two processes are also discussed.

Electron microscopic observations of immunoreactive cells in the rheumatoid synovial membrane

The perivascular infiltrates of the rheumatoid synovium were examined in the electron microscope. Lymphocyte-rich, plasma cell-rich, and transitional areas were observed. The transitional areas contained lymphocytes, plasma cells, blast cells, macrophages, and fribroblasts. Although lymphoblasts were frequent, the blast cells were predominantly plasmablasts. Marked degeneration of fibroblasts in the vicinity of lymphoblasts suggested the liberation of a lymphotoxin by the lymphoblasts. There was close contact between blast cells and macrophages and between macrophages and lymphocytes. The close association of lymphoblasts, plasmablasts, and macrophages in the transitional areas suggests that these are sites of T- and B-cell interaction in the rheumatoid synovial immune response.

Light and electron microscopic investigation of equine synovial membrane. A comparison between healthy joints and joints with intraarticular fractures and osteochondrosis dissecans

Light and electron microscopic examination was made on equine synovial membrane from 23 healthy joints, nine joints with synovitis caused by intraarticular fracture and 10 joints with synovitis caused by osteochondrosis dissecans. Histologically as well as ultrastructurally the equine synovial membrane from healthy joints was of principally the same character as described in other species. Three types of synovial membrane — areolar, fibrous and adipose — and two types of lining cell were distinguished histologically. Ultrastructurally three types of lining cells were distinguished: A and Β type and an intermediate cell type. In healthy joints they were loosely arranged, parallel to the joint surface in an intercellular matrix, which was in direct continuity with the joint space. In joints with intraarticular fracture there was mild inflammation of the synovial membrane. There was elongation and hyperplasia of the lining cells with a relative increase in type A cells. The cell surface of lining cells was increased through filopodia. There was also an increase in cytoplasmic organelles i.e. hyperplasia of rough endoplasmic reticulum and Golgi complexes in Β type cells and an increase in lysosomes, and increased numbers of vesicles of varying types in A cells. In joints with osteochondrosis dissecans the lining cell hyperplasia and the inflammation in the synovial membrane were more prominent. Ultrastructurally the same alterations as in the previous group were seen including a relative increase in the number of A cells but degenerative changes were common in the lining cells. These changes were dilatation and vesiculation of rough endoplasmic reticulum, mitochondrial condensation, dilatation of the nuclear envelope and loss of plasma membranes, leading to disintegration of cells.

Cellular contacts in the synovial membrane of the cat and the rabbit: an ultrastructural study

Regularly, four different types of cellular contacts are found in synovial folds and villi of the cobital joint of the cat (interdigitations, desmosomes, intermediate junctions, gap junctions). The same types of contact--with the exception of intermediate junctions--occur sporadically also in synovial fat folds of the knee joint of the rabbit. In both species, hemidesmosomes and discontinuous basement membranes are seen in the synovial lining layer. Cellular contacts predominate between A-cells and cells of the intermediate type, hemidesmosomes and incomplete basement membranes predominate in intermediate cells and B-cells. The latter are rare in A-cells. The importance of such contacts for mechanical, metabolic and electrical interactions of cellular elements in the synovial membrane is discussed. No unanimous concept as to their function can be advanced at present.

Joint effusions, chondrocalcinosis and other rheumatic manifestations in hypothyroidism. A clinicopathologic study

Twelve patients with severe hypothyroidism and rheumatic signs and symptoms were studied before or within four days of receiving thyroid replacement therapy. Eight patients had synovial effusions. Seven effusions were extremely viscous and six contained calcium pyrophosphate crystals. Leukocyte counts were less than 1,000/mm3, except in two patients during crystal-induced synovitis. "Bulge signs" were present but often sluggish, possibly because of the viscosity of the fluid. Flexor tendon sheath thickening, joint laxity and popliteal cysts were documented. All patients complained of generalized stiffness and two had proximal myopathy. Roentgenograms were obtained in 11 patients, and chondrocalcinosis was identified in seven. Needle synovial biopsy specimens in five patients showed only mild inflammation in the thick synovium. These findings can suggest hypothyroidism, a treatable disease, as the cause of musculoskeletal problems.

Ultrastructure of the synovial membrane

The normal synovial membrane as seen by electron microscopy is bordered by one to three layers of lining cells that include some with phagocytic function, others rich in endoplasmic reticulum for protein synthesis and additional cells with mixed properties. Lining cells with prominent Golgi apparatus probably produce the synovial hyaluronic acid. The synovial matrix contains collagen and mucopolysaccharide. It offers little barrier to diffusion of most materials. Superficial capillaries and venules are fenestrated and presumably allow rapid exchange of fluid and electrolytes. Deeper venules have thick endothelium that can separate at intracellular junctions and can phagocytize circulating particles. Other identified synovial structures are fibrocytes, macrophages, lymphatics, mast cells, non-myelinated nerves and fat.

The effect of sensory denervation on rabbits' knee joints. A light and electron microscopic study

Unilateral sensory denervation of the hind limb in a group of rabbits caused progressive atrophy of cells in all structures of the knee joint, whether or not the joint was protected by a plaster cast. Immobilization without denervation caused proliferative changes, first in the synovium and then in the articular cartilage. The initial changes in the articular cartilage following sensory denervation occurred in the middle layers, suggesting that nutritional deficiency was involved. In contrast, the first changes in the cartilage of intact immobilized limbs occurred in the superficial layers and were most likely of mechanical origin.

Electron microscopic studies of the cartilage-pannus junction in rheumatoid arthritis

The junction between pannus and cartilage was examined in the rheumatoid joint. Three types of cartilage-pannus junction were observed. In one, proliferating small blood vessels, surrounded by highly cellular infiltrates, penetrated deeply into the cartilage. Degeneration of the cartilage was observed around the cellular accumulations. In the second, phagocytic and fibroblastic cells invaded the cartilage. In the third, fibrous pannus overlay the cartilage. Lysis of cartilage by infiltrating cells appeared to be a major cause of cartilage erosion in rheumatoid arthritis.