Ultrastructure of synovial membrane in rheumatoid arthritis

Involvement of Epithelial-Mesenchymal Transition (EMT) in Autoimmune Diseases

Epithelial-mesenchymal transition (EMT) is a complex reversible biological process characterized by the loss of epithelial features and the acquisition of mesenchymal features. EMT was initially described in developmental processes and was further associated with pathological conditions including metastatic cascade arising in neoplastic progression and organ fibrosis. Fibrosis is delineated by an excessive number of myofibroblasts, resulting in exuberant production of extracellular matrix (ECM) proteins, thereby compromising organ function and ultimately leading to its failure. It is now well acknowledged that a significant number of myofibroblasts result from the conversion of epithelial cells via EMT. Over the past two decades, evidence has accrued linking fibrosis to many chronic autoimmune and inflammatory diseases, including systemic sclerosis (SSc), rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), Sjögren's syndrome (SS), and inflammatory bowel diseases (IBD). In addition, chronic inflammatory states observed in most autoimmune and inflammatory diseases can act as a potent trigger of EMT, leading to the development of a pathological fibrotic state. In the present review, we aim to describe the current state of knowledge regarding the contribution of EMT to the pathophysiological processes of various rheumatic conditions.

Inhibitory Effects of Cold Atmospheric Plasma on Inflammation and Tumor-Like Feature of Fibroblast-Like Synoviocytes from Patients with Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic, debilitating systemic disease characterized by chronic inflammation and progressive joint destruction. Fibroblast-like synoviocytes (FLSs) are one of the most important players in the pathophysiology of RA, acting like tumor cells and secreting inflammatory cytokines. Previous research has shown that cold atmospheric plasma (CAP) inhibits cancer cells and may have anti-inflammatory properties. This study examined the effects of argon plasma jet-produced CAP on the suppression of invasion and inflammation caused by cultured RA-FLS. The findings revealed that CAP reduced cell viability and elevated the percentage of apoptotic RA-FLS by producing reactive oxygen species. Carboxyfluorescein diacetate succinimidyl ester (CFSE) staining confirmed that CAP could decrease the proliferation of RA-FLS. Furthermore, CAP effectively reduced the production of inflammatory factors (e.g., NF-κB and IL-6) as well as destructive factors like receptor activator of nuclear factor kappa-B ligand (RANKL) and matrix metalloproteinases-3 (MMP-3). These data suggest that CAP could be a promising treatment for slowing the progression of RA by reducing tumor-like features and inflammation in RA-FLS.

Spontaneously Resolving Joint Inflammation Is Characterised by Metabolic Agility of Fibroblast-Like Synoviocytes

Fibroblast-like synoviocytes (FLS) play an important role in maintaining joint homeostasis and orchestrating local inflammatory processes. When activated during injury or inflammation, FLS undergo transiently increased bioenergetic and biosynthetic demand. We aimed to identify metabolic changes which occur early in inflammatory disease pathogenesis which might support sustained cellular activation in persistent inflammation. We took primary human FLS from synovial biopsies of patients with very early rheumatoid arthritis (veRA) or resolving synovitis, and compared them with uninflamed control samples from the synovium of people without arthritis. Metabotypes were compared using NMR spectroscopy-based metabolomics and correlated with serum C-reactive protein levels. We measured glycolysis and oxidative phosphorylation by Seahorse analysis and assessed mitochondrial morphology by immunofluorescence. We demonstrate differences in FLS metabolism measurable after ex vivo culture, suggesting that disease-associated metabolic changes are long-lasting. We term this phenomenon 'metabolic memory'. We identify changes in cell metabolism after acute TNFα stimulation across disease groups. When compared to FLS from patients with early rheumatoid arthritis, FLS from patients with resolving synovitis have significantly elevated mitochondrial respiratory capacity in the resting state, and less fragmented mitochondrial morphology after TNFα treatment. Our findings indicate the potential to restore cell metabotypes by modulating mitochondrial function at sites of inflammation, with implications for treatment of RA and related inflammatory conditions in which fibroblasts play a role.

Nomenclature clarification: synovial fibroblasts and synovial mesenchymal stem cells

Synovial-derived cells, found in the synovial membrane of human joints, were obtained by digestion of the synovial membrane and were subsequently expanded in vitro. The identity of synovial-derived cells has long been a topic of debate. The terms "type B synoviocytes," "fibroblast-like synoviocytes (FLS)," "synovium-derived mesenchymal stem cells (MSCs)," and "synovial fibroblasts (SF)" appeared in different articles related to human synovial-derived cells in various disease models, yet they seemed to be describing the same cell type. However, to date, there is no clear standard to distinguish these terms; thus, the hypothesis that they represent the same cell type is currently inconclusive. Therefore, this review aims to clarify the similarities and differences between these terms and to diffuse the chaotic nomenclature of synovial-derived cells.

Ultrastructure of the Synovial Membrane in Seronegative Inflammatory Arthropathies

The ultrastructure of the synovial membrane has been studied in 6 patients with seronegative inflammatory arthropathies: Reiter's (2), Crohn's (2), Whipple's (1) and Behcet's disease (1). The most striking changes were found in the synovial B cells, many containing abnormally large mitochondria with altered cristae surrounded by fibrillar material. Similar material was present in dilated endoplasmic reticulum which was the probable source of groups of extracellular fibrillar spheroidal bodies. The B cells also contained electron dense granular lysosomes of very variable size which, in common with the abnormal mitochondria, were often associated with bundles of orientated microfilaments and large golgi complexes. Light microscopy of the synovial membrane was consistent with an inflammatory arthritis, as were the high white cell counts in the synovial fluid. Systemic activity in the patients was indicated by raised ESR and C-reactive protein (CRP).

A CCR2 macrophage endocytic pathway mediates extravascular fibrin clearance in vivo

Extravascular fibrin deposition accompanies many human diseases and causes chronic inflammation and organ damage, unless removed in a timely manner. Here, we used intravital microscopy to investigate how fibrin is removed from extravascular space. Fibrin placed into the dermis of mice underwent cellular endocytosis and lysosomal targeting, revealing a novel intracellular pathway for extravascular fibrin degradation. A C-C chemokine receptor type 2 (CCR2)-positive macrophage subpopulation constituted the majority of fibrin-uptaking cells. Consequently, cellular fibrin uptake was diminished by elimination of CCR2-expressing cells. The CCR2-positive macrophage subtype was different from collagen-internalizing M2-like macrophages. Cellular fibrin uptake was strictly dependent on plasminogen and plasminogen activator. Surprisingly, however, fibrin endocytosis was unimpeded by the absence of the fibrin(ogen) receptors, αMβ2 and ICAM-1, the myeloid cell integrin-binding site on fibrin or the endocytic collagen receptor, the mannose receptor. The study identifies a novel fibrin endocytic pathway engaged in extravascular fibrin clearance and shows that interstitial fibrin and collagen are cleared by different subsets of macrophages employing distinct molecular pathways.

Development and histologic characteristics of synovitis induced by trauma in the rat temporomandibular joint

Histopathological changes caused by trauma to the rat temporomandibular joint synovium were examined by light microscopy. The trauma was induced by forced hypermobility of the condyle. Pathological changes of the synovium were found primarily in the anterior pouch of the upper joint compartment. The main findings included surface cell proliferation, increased capillary hyperemia, fibrin deposits on the surfaces of inflamed synovial membranes, and fibrinous adhesion between closely opposed synovial membranes. A gradual change from fibrinous adhesion to fibrous adhesion was also seen.

Light microscopic characterization of the fibroblast-like synovial intimal cell (synoviocyte)

OBJECTIVE

To reassess synovial intimal cell populations by light microscopy.

METHODS

Non-inflamed, rheumatoid and osteoarthritic synovia were analyzed as tissue sections and cytospin preparations by a series of combined immunohistochemical and cytochemical staining techniques.

RESULTS

Two populations of intimal cells were identified. The first carried macrophage markers. The second showed high uridine diphosphoglucose dehydrogenase (UDPGD) activity, minimal cytoplasmic CD68, absent non-specific esterase (NSE) activity, and absent leukocyte and endothelial antigens. The majority of these cells showed a high content of prolyl hydroxylase.

CONCLUSION

Combined cytochemical staining for NSE and UDPGD activity allows effective separation of intimal cell populations. We suggest that the cells of high UDPGD activity are the fibroblast-like or type B synovial intimal cells defined by electron microscopy. High UDPGD activity probably reflects a preferential ability to synthesize glycosaminoglycans, including hyaluronan.

Fine structure of the human synovial lining cell in osteoarthritis: its prominent cytoskeleton

The cytoskeleton of the human osteoarthritic synovial lining cell (SLC) consists of an extensive number of vimentin intermediate filaments (IFs) in addition to microfilaments and microtubules. The IFs are especially prevalent in the SLC processes, but are commonly seen in a paranuclear arrangement. Processes, ending in numerous microvilli and blebs, project into the joint space. Scanning electron microscopy (SEM) further reveals the processes that may parallel the synovium surface for a short distance. IFs extend to the termination of such Numerous pinocytotic vesicles and extensive rough endoplasmic reticulum (rER) are characteristic of the type B cells. Lysosomes and long microvilli identify the type A cell. Punctate adherens, gap junctions, and cilia are the cell membrane specializations of the osteoarthritis (OA) synovium. A comparison with synovium from rheumatoid arthritis (RA) patients is made in order to assess the effect o this inflammatory disease on the SLC cytoskeleton, cell type relationship, and cell arrangement. The prominent cytoskeleton appears to play an important role in the architecture of the synovium. Our findings are further presented in the form of a drawing which in some aspects could describe the morphology of the normal synovium.

Potential mechanisms for coordinate gene activation in the rheumatoid synoviocyte: implications and hypotheses

Evidence is reviewed to support the concept that synovial cells in rheumatoid arthritis have undergone distinctive alterations at the cellular and subcellular level that result in their taking on some of the characteristics that are also manifest by transformed cells. These phenotypic modulations could be indirectly driven by cytokines in a paracrine or autocrine fashion. Specific regional patterns of cell phenotype modulation were used to argue against a simple widely diffusing direct inductive effect to cytokines and in favor of microenvironmental determinants. It is hypothesized that these extracellular factors induce novel activation in a coordinate manner by acting through master regulatory genes operating in cells with specific microenvironmental interactions. Two of these regulatory genes, fos and jun, are discussed in detail because of their induction by growth factors and their central role in the transactivation of genes which have been implicated in rheumatoid synovitis. A model for gene activation in the rheumatoid synovium is proposed based on the premise that fos and jun are an important link in the intracellular transduction pathways used by cytokines to induce cellular phenotypic changes.

Arthritis-associated changes in flow cytometric characteristics of cultured synovial fibroblasts

Synovial fibroblasts cultured from patients with rheumatoid or reactive arthritis and from controls were studied by flow cytometry, spectroscopy, and electron microscopy. Analysis of 29 cell lines revealed consistent differences between arthritic and normal fibroblasts. Cells cultured from inflamed synovial tissue exhibited higher autofluorescence than did control fibroblasts, and displayed exceptional light scatter properties in flow cytometry, indicating changes in cytoplasmic structures. Electron microscopic examination of the fibroblasts from arthritic synovial tissue revealed large numbers of round, swollen, laminated, mitochondrion-like bodies, which were not observed in the control fibroblasts. The changes observed by flow cytometry (light scatter and autofluorescence) coincided with the presence of the mitochondrion-like organelles. The strong autofluorescence observed in the arthritic fibroblasts resembled the fluorescence spectrum of mitochondrial flavoproteins. These data suggest that persistent metabolic and structural changes have occurred in the mitochondria of synovial fibroblasts and inflammatory synovial tissue. The usefulness of flow cytometry in identifying such cells is described.

Autoantibodies from rheumatoid arthritis patients recognize antigens on the synoviocyte surface

We have found autoantibodies in the sera from rheumatoid arthritis (RA) patients which recognize two cell surface antigens of approximately 70 kDa and 28 kDa from synoviocyte extracts as detected by immunoprecipitation analysis. These polypeptides were immunoprecipitated from extracts containing mainly macrophage-like synoviocytes (type A) but not from extracts of homogeneous fibroblast-like synoviocytes (type B). These autoantigens are not selectively expressed by RA synoviocytes, since both RA and non-rheumatoid synovia were reactive for RA sera. From the panel of different RA sera tested, 64% immunoprecipitated the 70 kDa band, and 27% recognized the 28 kDa polypeptide. These differences in the specificity of the sera seemed to be related to the clinical state of the donor. The sera from patients suffering from other autoimmune diseases such as autoimmune thyroiditis and systemic lupus erythematosus (SLE) do not appear to be reactive for these specificities, but sera from patients with Sjögren's syndrome, psoriatic arthritis, and Crohn's disease showed a weak cross-reactivity with the 70 kDa polypeptide. This autoreactivity against synovial cells in RA supports the idea that these cells participate in the initial immune response of the disease.

Activated monocytes induce arthritis-associated changes in mitochondria of cultured synovial fibroblasts

We have recently shown that synovial fibroblasts cultured from patients with reactive or rheumatoid arthritis exhibit increased autofluorescence when compared with controls. Morphological studies suggested that this increase was related to the anomalous structure of mitochondria in cells cultured from rheumatoid or non-rheumatoid inflammatory synovial tissue. The present study describes attempts to find an explanation for these observations. The effects of conditioned media of cultured mononuclear cells were tested on normal synovial fibroblasts. Conditioned media of monocytes stimulated with lipopolysaccharide or poly-IC induced an increase in the cellular autofluorescence and changes in the morphology of mitochondria in normal fibroblasts. These changes were indistinguishable from those seen in synovial fibroblasts cultured from various arthritides. Indomethacin or gold salts did not abolish the effects of monocyte-conditioned media. Abnormal mitochondria could not be induced in the presence of cycloheximide. This study describes a new aspect of monocyte-fibroblast interactions during rheumatoid and non-rheumatoid inflammation of synovial tissue.

On the presence of rheumatoid factor in joints before and after synovectomy

The presence of rheumatoid factor in synovial fluid has been investigated before and after synovectomy. The sensitized sheep cell test (SSC) and acryl fixation test were used. Fourteen patients representing 18 knee joints in which synovectomy was performed, showed the same immunologic conditions in the synovial fluid before and after the surgical procedure. The relationship between the presence of immunoglobulins and certain structural features in the synovial tissue is discussed.

Relationship between iron deposits and tissue damage in the synovium: an ultrastructural study

A detailed ultrastructural study was made of the synovial iron deposits in cases of haemophilic synovitis (HS), pigmented villonodular synovitis (PVNS), rheumatoid arthritis (RA), osteoarthritis (OA), seronegative inflammatory arthritis (SNA), and in controls, to investigate the relationship between iron deposits and tissue damage. Iron was seen by electron microscopy in about 75% of synovial lining cells in HS and PVNS but only in about 25% of synovial cells from cases of RA and SNA. In cases of OA and in controls iron deposits were scarce. The iron was usually deposited within pleomorphic siderosomes and in HS was most common in type A synovial cells. In contrast, deposits in all other cases were more common in type B cells, which were frequently the predominant cell type, and siderosomes were smaller, more homogeneous, and were more common in deeper synovial tissue. Considerable tissue damage was noted in the vicinity of iron rich siderosomes in synovial A cells from cases of HS, but such deposits in B cells in the synovium from the other cases had relatively little effect. We discuss the possibility that such differences directly reflect the differing functions of type A and B synovial cells, and particularly their relative ability to produce metabolically active oxygen metabolites with tissue destructive potential in the presence of iron.

Extracellular matrix-cytoskeletal interactions in rheumatoid arthritis. I. Immunoelectron microscopic analysis of the fibronexus at the adhesive surface of normal porcine type B synoviocytes in vitro

We studied cell surface interactions between the fibronectin (FN)-containing extracellular matrix and the actin cytoskeleton of normal porcine synoviocytes in vitro, using electron microscopic methods. These type B synovial cells were distinguishable from dermal fibroblasts co-isolated from the same organism, because of their very long cellular processes and their ability to synthesize prostaglandin E2 after stimulation with interleukin-1. With plastic sections, we found end-to-end (tandem) and track-like (lateral) transmembrane associations of extracellular fibers and cortical 5-nm microfilaments localized along the attenuated synoviocyte processes in postconfluent cultures. Very similar FN-actin complexes, termed fibronexus (FNX), have been observed on cultured fibroblasts and on granulation tissue myofibroblasts in vivo. Using double-label immunoelectron microscopy with monospecific antibodies applied to ultrathin frozen sections of synoviocytes cut in situ, we proved that these FNX were indeed composed of associated FN and actin filaments. The striking finding of numerous FNX in cultured type B synoviocytes strongly suggests that the FNX is a major cell surface adhesion site in normal synovium, which may play an important role in pannus formation, connective tissue remodeling, and synoviocyte proliferation in patients with rheumatoid arthritis.

Ultrastructural changes in the rectal mucosa of patients with rheumatoid arthritis

The rectal mucosa from patients with severe rheumatoid arthritis has been examined by electron microscopy. Initially the patients were biopsied for investigation into the diagnosis of amyloidosis or vasculitis, which proved to be negative. A range of ultrastructural abnormalities was found which included proliferation of the rough endoplasmic reticulum, mitochondrial inclusions, association of the mitochondria with cytoplasmic filaments, and marked increase in the number of iron containing siderosomes. Most of these abnormalities have already been reported in rheumatoid synovial tissue, and attention is drawn to the similarity in findings between these two sites.

Changes in vascular endothelium related to lymphocyte collections in diseased synovia

A population of small blood vessels are described in the synovia of patients with a number of different arthropathies. These vessels are identical to the high endothelial venules (HEV) of lymph node paracortex, known to be the site of lymphocyte diapedesis from blood to tissues. The significance of this finding and its possible role in the pathogenesis of inflammatory arthritides are discussed.

Ultrastructure of synovial changes in rheumatoid disease and in seronegative inflammatory arthropathies

Synovial tissue has been examined by electron microscopy from patients suffering from either sero-positive or sero-negative inflammatory arthropathies to allow direct comparison of the ultrastructural changes found in these groups and to confirm and extend observations previously made in a smaller group of sero-negative arthropathies. Both groups have been compared with material from healthy controls. The sero-positive group comprised 13 cases of 'definite' or 'classical' rheumatoid arthritis. The sero-negative group consisted of 9 cases of arthritis secondary to Crohn's disease (3); Reiter's syndrome (2); Whipple's disease (1); Behcet's disease (1); Wegener's granulomatosis (1) and ankylosing spondylitis (1). The control tissue was obtained from 6 non-arthritic subjects undergoing surgery for non-inflammatory conditions. Confirmation was obtained of changes previously reported in subcellular organelles, especially in synovial B cells, in all forms of inflammatory arthritis as compared with controls. Attention is now drawn to other intracellular changes in B cells and intermediate cells which included: a marked increase of intermediate filaments and microfilaments: and proliferation of pinocytotic vesicles and rough endoplasmic reticulum. These changes were often accompanied by the presence, in the immediate environment of these cells, of extracellular microfibrillary masses but little or no accumulation of intermediate filaments. It was confirmed that synovial A cells were reduced in number but showed changes suggestive of increased phagocytic activity and also exhibited proliferation of cytoskeletal elements. Differences in these structural changes between sero-positive and sero-negative arthritis were of degree rather than of kind and no 'specific' or diagnostic differences were observed between the various forms of seronegative athropathies. The possible significance of the structural changes observed is discussed.

Intermediate filaments in synovial lining cells in rheumatoid arthritis and other arthritides are of vimentin type

Cryostat section of synovial tissue from patients with rheumatoid arthritis, ankylosing spondylitis, osteoarthrosis, pigmented villonodular synovitis, and from a normal knee were studied by indirect immunofluorescence with guinea-pig antibodies to the intermediate filament proteins prekeratin, vimentin, and desmin. Staining for vimentin, but absence of prekeratin and desmin, was demonstrated in synovial lining cells. Antivimentin antibody also stained synovial tissue fibroblasts and vascular endothelial lining cells. The intensity of fluorescent staining for vimentin broadly correlated with cellular proliferative activity at these 3 sites.

Lysosomal elastase: effect on mechanical and biochemical properties of normal cartilage, inhibition by polysulfonated glycosaminoglycan, and binding to chondrocytes

Rheumatic joint destruction usually starts with the destabilisation of cartilage. Lysosomal elastase is a candidate effector of this process, since this enzyme is found at the site of cartilage erosion by rheumatoid synovial tissue. In order to prove this hypothesis we assessed the mechanical stability of cartilage during treatment by this enzyme in vitro. An indentation apparatus was used for this purpose and biochemical as well as microscopic techniques were used to supplement the results thus obtained. Our findings show that elastase irreversibly impairs the stability of cartilage by lysis of matrix proteoglycans without the help of additive enzymes. Collagen fragmentation played no significant role during elastase-induced destabilisation, while specific collagenase attacked the collagen network within the matrix only subsequent to the removal of proteoglycans. These findings suggest that elastase is a leading enzyme during proteolytic cartilage degradation. In addition polysulfonated glycosaminoglycan was found to reduce the mechanical effect of elastase on normal cartilage. It is therefore concluded that local inhibition of elastase promises therapeutic benefit during rheumatic cartilage degradation. Upon treatment of cartilage with elastase we observed this enzyme not only within the matrix under destruction but also bound to chondrocytes. These findings support the hypothesis that elastase plays a role on the matrix not only by direct degradation, but also by an indirect effect mediated through living chondrocytes.

Pinocytosis in human synovial cells in vitro. Evidence for enhanced activity in rheumatoid arthritis

Human synovial tissue cells in monolayer can be shown to take up and digest a soluble protein, horseradish peroxidase (HRP). Uptake of HRP was linear with increasing concentrations of substrate and cell protein and with time for up to 4 h. Low temperature (4 degrees C), and sodium fluoride, an inhibitor of glycolysis were the most effective metabolic inhibitors of endocytosis. In addition, colchicine, an inhibitor of microtubule assembly, and yeast mannan, an inhibitor of mannose-specific receptors, reduced HRP uptake. Synovial cells from patients with rheumatoid arthritis (RSC) demonstrated a statistically significantly higher rate of endocytosis (247 +/- 107 ng HRP/100 micrograms cell protein per 2 h.) than cells from control, nonrheumatoid patients (NSC) (100 +/- 80 ng HRP/100 micrograms cell protein per 2 h). Thus, it is possible to discriminate RSC from NSC by their quantitatively different rates of endocytosis. Digestion of HRP by synovial cells is statistically significant by 6 h after uptake. A faster initial rate of digestion was seen in RSC. Over the first 6--8 h of incubation 42% of the endocytosed HRP was still cell-associated in RSC and 67% remained in NSC cultures. However, by 24 h 20--30% of endocytosed HRP was found in both types of cultures. These results indicate that endocytosed molecules may accumulate more rapidly in RSC and persist within their lysosomes for a longer time than in NSC. The quantitative determination of enhanced endocytosis by RSC compared with NSC suggests that this increased activity may have a role in the pathological function of synovial tissue in rheumatoid arthritis.

Overview article: the articular territory of the reticuloendothelial system

It has long been recognized that synovial intimal cells are phagocytic and that they are capable of picking up colloidal or particulate material injected into the circulation. Hence they have been described as the "articular territory of the reticuloendothelial system." Ultrastructural studies have added a wealth new knowledge and details about the remarkable endocytotic powers of synovial cells. It has been shown that they can endocytose not only small particulate substances like colloidal iron, colloidal gold, and thorotrast but also relatively large objects like masses of fibrin and entire erythrocytes. Controversy has arisen as to whether it is the Type A or Type B cell that is the main scavenger of the joint. Evidence will be presented to show that this is a somewhat fictitious controversy and that these are not distinct and different races of cells with different functions but merely cells whose differences in morphology reflects the function they are performing at a given moment.

Cellular junctions in normal and inflammatory human synovial membrane revealed by tannic acid and freeze fracture

Cellular junctions between synovial cells and endothelial cells of the microvasculature were examined in 10 normal and 20 inflammatory human synovial membranes by means of tannic acid and freeze fracture, Gap junctions and desmosomes predominated on synovial cells, and tight junctions in the microvasculature. Comparison between normal and inflammatory synovial membranes did not demonstrate changes in cellular contacts that might be caused by inflammation.

Ultrastructural localization and in situ analysis of iron, bismuth, and gold inclusions

The purpose of this article is to review ultrastructural and electron probe X-ray analytical studies on metallic deposits in cells. The metals that will be dealt with are iron, bismuth, and gold, mainly because they have been extensively studied in recent years. The nature and chemical composition of endogenously (e.g., from breakdown of autologous blood) and exogenously (e.g., after a transfusion or injection of iron compounds) produced hemosiderin (i.e., iron deposits) has been the subject of time-hallowed controversies. Quite a few of these have now been resolved by ultrastructural studies and the atomic composition of such deposits has been determined by electron probe X-ray analysis. The interest in bismuth centers around the fact that this is one of the two metals (the other being lead) that produces quite large intranuclear inclusions. Here again much has been learned by ultrastructural and X-ray analytical studies. The interest in gold stems from the fact that soluble salts of this metal are used for the treatment of rheumatoid arthritis and current studies with the above-mentioned techniques indicates how gold produces its beneficial and toxic effects.

A mechanism of formation of desmosome-like structures between synovial intimal cells

Desmosomes or desmosome-like structures do not occur between normal synovial cells but such structures do develop between the synovial cells in cases of traumatic arthritis, rheumatoid arthritis and villonodular synovitis. Morphological evidence is presented suggesting that such structures develop as a result of the interaction of fibrin trapped between synovial cells and the plasmamembrane of these cells.

Ultrastructure of the skin of patients treated with sodium aurothiomalate

Skin biopsies from cases of rheumatoid arthritis treated with sodium aurothiomalate were examined with the electron microscope. Intralysosomal gold deposits were found in the macrophages of both normal-looking skin and from areas of erythematous rash that had developed as a toxic manifestation of gold therapy. The main difference between affected and normal-looking skin was the presence of numerous mast cells in the former. It is hence suggested that the dermatologic side-effects of gold are probably mediated by the release of vasoactive substances from mast cells and that vigorous administration of antihistamines to neutralise the liberated products of mast cells or an agent that interferes with degranulation of mast cells might have a palliative effect on the skin rash that sometimes develops during chrysotherapy.

Aurosomes produced in the synovial membrane by the oral administration of a gold compound SK & F 36914

Chlorotriethylphosphine gold (SK & F 36914) administered orally to rabbits produced aurosomes in the synovial membrane. These aurosomes were similar to aurosomes produced by parenteral or intra-articular injections of soluble gold salts such as sodium aurothiomalate and aurothioglucose. This study shows, (1) that an orally administered gold compound is capable of producing gold deposits in the synovial membrane, and (2) that such compounds may have a future in the treatment of rheumatoid arthritis.

The biology of the rheumatoid synovial cell

Over the past 15 years, many of the elaborate research techniques of cell biology and biochemistry have been applied toward discovering the cause of rheumatoid arthritis. Consequently, it is valuable to review the morphological, physiological and biochemical alterations that have been observed in rheumatoid synovial cells. All of the changes observed suggest that a viral agent may form the basis for these alterations. However, studies to date have failed to isolate or identify the putative causative virus and the search continues.

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.

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.

A malignant tumor of the vagina resembling synovial sarcoma: a light and electron microscopic study

A malignant tumor arising in the upper lateral vaginal mucosa in a 24-year-old white woman, hitherto undescribed in the literature, was studied by light and electron microscopy. The main part of the tumor was epithelioid, forming a tubular or acinar pattern. At the periphery, the tumor cells were more spindly and formed sheets resembling fibrosarcoma. The tumor cells contained occasional material positive for mucicarmine, alcian blue, and PAS stains, and the nests of the cells forming acini were surrounded by reticulin fibers. The tumor ultrastructure consisted of a single type of cell with large cytoplasmic vacuoles and occasional perinuclear intracytoplasmic filaments. Slender long microvilli projecting into the lumina were also characteristic. Basal laminae were occasionally present around the acini. The findings suggested that the tumor was of mesenchymal origin, closely related to synovial sarcoma.

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.

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.

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.

Synovial membrane and fluid morphologic alterations in early rheumatoid arthritis: microvascular injury and virus-like particles

Eight patients have been studied during the first 6 weeks of rheumatoid synovitis. All of them exhibited microvascular injury, which was manifested by gaps between endothelial cells, vascular occlusion, erythrocyte extravasation, or endothelial cell injury. In four patients, a variety of virus-like particles were found associated with the endothelium or perivascular cells. In two cases, particles were seen in electron-dense deposits in vessel walls. Lymphocytes and PMN infiltrated the synovial membranes, but plasma cells were uncommon. Evidence of phagocytosis was prominent in synovial lining cells and other large mononuclear cells, but not in PMN. These observations are consistent with injury to synovium and, specifically, synovial vessels as an early stage in RA synovitis. The virus-like particles require further investigation, because nonviral cell components remain very difficult to distinguish in electron microscopy tissue sections.