Synovial Intimal Cells Research Articles

Cannabinoid receptors are expressed in equine synovium and upregulated with synovitis.

Osteoarthritis (OA) is a major cause of equine lameness. Cannabinoid (CB) receptors are now considered to be promising therapeutic targets in human rheumatology for pain and inflammation, however, little is known about the equine endocannabinoid system. The primary goal was to assess the presence and expression pattern of CB1 and CB2 in the synovium of healthy joints. A secondary goal was to explore the relationship between the CB expression, degree of synovitis and OA pathology. Ex vivo experimental study. Metacarpophalangeal joints (n=25) from a tissue bank were studied. The joints were dissected, and the articular cartilage lesions were scored. Synovial membrane specimens (n=45) were harvested, fixed and the degree of synovitis was graded on histological sections. Colocalised synovial sections were also immunostained with antibodies to CB1 and CB2. Five regions of interest were randomly selected from digital images of manually segmented synovial intima and scored blindly for positive cellular immunoreactive staining by two independent observers. Interobserver agreement was calculated with an intraclass correlation coefficient (ICC). Relationships between CB1 and CB2 immunoreactive scores and synovitis or joint OA grade were explored with mixed linear models. CB1 was expressed in synovial intimal cells in all specimens studied whereas CB2 expression was identified in 94%. Both receptors were also expressed in the subintimal blood vessel walls. ICCs were 84.6% (CB1) and 92.9% (CB2) for the immunoreactivity scores. Both CB1 and CB2 expression were significantly upregulated (p=0.04 and p=0.03, respectively) with increasing degree of synovitis. Conversely, CB1 expression significantly decreased (p=0.03) with increasing severity of OA. The type of synovial cell expressing CB1 or CB2 was not investigated. Equine synovial intimal cells constitutively express both CB1 and CB2 receptors that are upregulated with synovitis and may have a role in joint pain. They are potential targets for therapy with cannabinoid molecules or their derivatives.

Podoplanin (D2-40) and Clusterin Are Reliable Markers of Normal and Inflamed Synovium

Synovial lining cells (“intima”) arise from a proliferation of fibroblast-like cells and recruitment of macrophage-like cells from the circulation. Recent work has shown that synovial intimal cells are positive for clusterin (CLU) and podoplanin (PP). CLU has been noted to mark nonneoplastic synovium adjacent to tenosynovial tumors, and some studies suggest that PP …

Effects of continuous intra-articular infusion of gentamicin on synovial membrane and articular cartilage in the tarsocrural joint of horses.

To determine the effects of a continuous intra-articular infusion of gentamicin on the synovial membrane and articular cartilage in the tarsocrural joint of horses. 6 healthy adult horses. A balloon infusion system attached to a catheter placed in the plantarolateral pouch of both tarsocrural joints in each horse was used for continuous gentamicin solution (GM) or balanced electrolyte solution (BES) delivery for 5 days. Cartilage and synovial membrane specimens were collected on day 5 from 3 horses and on day 14 from the remaining 3 horses. Both infused joints from each horse were assessed, using gross evaluation and histologic scoring systems. Significant differences in the histologic scores of synovial membrane specimens between the GM- and BES-treated joints at either 5 or 14 days were not observed. Safranin-O-fast green staining scores were similar between cartilage specimens from GM- and BES-treated joints. Although the synovial membrane histologic scores and safranin-O-fast green staining scores improved from day 5 to 14, the changes in scores were not significant. Loss of synovial intimal cells from villi was found more commonly in sections of synovial membrane from GM-treated joints, compared with BES-treated joints. Continuous infusion of GM into the tarsocrural joint of horses does not have significant effects on histologic scores of articular cartilage or synovial membrane, compared with those infused with BES. Continuous infusion of GM into the tarsocrural joint of horses for 5 days is an acceptable method for the treatment of septic arthritis.

Insulinlike growth factor-I gene therapy applications for cartilage repair.

Cartilage function after resurfacing with cell-based transplantation procedures or during the early stages of arthritic disease may be bolstered by the addition of growth factor genes to the transplanted tissue. Insulinlike growth factor-I maintains chondrocyte metabolism in normal cartilage homeostasis and has been shown to improve cartilage healing in vivo. Given the relatively short half-life of insulinlike growth factor-I in biologic systems, however, maintenance of effective concentrations of this peptide has necessitated either very high initial doses or repeated treatment. Delivery of the insulinlike growth factor-I gene, using a deleted adenovirus vector, specifically targeting graftable articular chondrocytes, bone marrow-derived chondroprogenitor cells, or synovial lining cells, may provide more durable insulinlike growth factor-I fluxes to articular tissues. Cultured equine articular chondrocytes, mesenchymal stem cells, synovial explants, and synovial intimal cells were readily transfected with an E1-deleted adenoviral vector containing equine insulinlike growth factor-I coding sequence. Optimal viral concentrations for effective transduction were 100 multiplicities of infection in synoviocytes, 500 multiplicities of infection in chondrocytes, and 1000 multiplicities of infection in mesenchymal stem cells. Production of insulinlike growth factor-I ligand varied from 65 ng/mL to 246 ng/mL in medium from chondrocytes and synovial explants, respectively. For chondrocytes, these concentrations were sufficient to produce significant stimulation of cartilage matrix gene expression and subsequent proteoglycan production. Moreover, cells in infected cultures maintained a chondrocytic phenotype and continued to express elevated insulinlike growth factor-I levels during 28 days of monolayer culture. Minimal synthetic activity, other than insulinlike growth factor-I ligand synthesis, was evident in synovial cultures. These experiments suggest several avenues for insulinlike growth factor-I supplementation of articular cartilage, including preimplantation adenoviral-insulinlike growth factor gene transfer to chondrocytes or chondroprogenitor cells, and direct injection of adenoviral-insulinlike growth factor to transfect the synovial structures in situ.

Samarium 153-labeled hydroxyapatite microspheres for radiation synovectomy in the horse: a study of the biokinetics, dosimetry, clinical, and morphologic response in normal metacarpophalangeal and metatarsophalangeal joints.

To determine the effects of Samarium-153 bound to hydroxyapatite microspheres (153SmM) when injected into the metacarpophalangeal and metatarsophalangeal joints of horses. - Horses were injected with 153SmM in metacarpophalangeal and metatarsophalangeal joints with the diagonal contralateral joints used as untreated controls. Twelve adult horses without pre-existing disease involving the metacarpo/metatarsophalangeal joints. Horses were divided into three groups: high-dose Samarium-153 (12.5 to 17.0 millicurie [mCi]), intermediate dose (6.5 to 12.0 mCi), and low dose (3.5 to 6.0 mCi). Horses were examined daily for 7 days postinjection for clinical abnormalities, lameness, and surface and systemic radiation levels. One horse from each group was euthanatized at 14, 30, and 60 days postinjection and the effects of the 153SmM examined microscopically in the cartilage and synovial membrane. Intraarticular(153)SmM caused inflammation characterized by lameness, effusion, and regional edema for 48 to 72 hours. Minimal levels of active 153SmM were identified in the blood or urine and were well below the maximal tolerance of 1 mCi. Microscopically the radiation caused no effects on the articular cartilage. The synovectomy created was good but not ideal in that some areas did have necrosis into the subintimal regions and a few islands of intact intimal cells persisted. The use of 153SmM is an effective means of targeting the synovial intimal cells with minimal extrasynovial leakage of radiation. The metacarpophalangeal and metatarsophalangeal joints of the horse can be safely treated with 153SmM without damage to the cartilage or significant extracapsular leakage.

Morphology and functional roles of synoviocytes in the joint.

The joint capsule exhibits a unique cellular lining in the luminal surface of the synovial membrane. The synovial intimal cells, termed synoviocytes, are believed to be responsible for the production of synovial fluid components, for absorption from the joint cavity, and for blood/synovial fluid exchanges, but their detailed structure and function as well as pathological changes remain unclear. Two types of synoviocytes, macrophagic cells (type A cells) and fibroblast-like cells (type B cells) have been identified. Type A synoviocytes are non-fixed cells that can phagocytose actively cell debris and wastes in the joint cavity, and possess an antigen-presenting ability. These type A cells, derived from blood-borne mononuclear cells, can be considered resident macrophages (tissue macrophages) like hepatic Kupffer cells. Type B synoviocytes are characterized by the rich existence of rough endoplasmic reticulum, and dendritic processes which form a regular network in the luminal surface of the synovial membrane. Their complex three-dimensional architecture was first revealed by our recent scanning electron microscopy of macerated samples. The type B cells, which are proper synoviocytes, are involved in production of specialized matrix constituents including hyaluronan, collagens and fibronectin for the intimal interstitium and synovial fluid. The proliferative potentials of type B cells in loco are much higher than type A cells, although the transformation of subintimal fibroblasts into type B cells can not be excluded. In some mammals, type B cells show features suggesting endocrine and sensory functions, but these are not recognized in other species. The synoviocytes, which form a discontinuous cell layer, develop both fragmented basement membranes around the cells and junctional apparatus such as desmosomes and gap junctions. For an exact understanding of the mechanism of arthritis, we need to establish the morphological background of synoviocytes as well as their functions under normal conditions.

An immunocytochemical study of the distribution of proline-4-hydroxylase in normal, osteoarthritic and rheumatoid arthritic synovium at both the light and electron microscopic level.

The monoclonal antibody 5B5 reacts with the beta subunit of proline-4-hydroxylase, the enzyme which catalyses the formation of 4-hydroxyl proline in collagen and other proteins with collagen-like amino acid sequences. This study aims to assess the production and tissue distribution of this enzyme in normal and diseased synovia from patients with various joint diseases, on the basis that it is a putative marker of collagen-producing cells and, therefore, in this context, of fibroblasts. Sections from five normal, 10 osteoarthritic (OA) and 26 rheumatoid arthritic (RA) synovia were labelled with a mouse monoclonal antibody to proline-4-hydroxylase. The enzyme was found to be expressed by a proportion of synovial intimal cells and by fibroblasts in the underlying connective tissue in normal, OA and RA synovia. Labelling was more pronounced in OA and RA cases. The intimal cells labelling positively showed type B synoviocyte morphology, which was confirmed by subsequent double immunolabelling with 5B5 and antibody against type IV collagen using immunocytochemistry and immunoelectron microscopy.

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

To reassess synovial intimal cell populations by light microscopy. Non-inflamed, rheumatoid and osteoarthritic synovia were analyzed as tissue sections and cytospin preparations by a series of combined immunohistochemical and cytochemical staining techniques. 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. 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.

Type IV collagen and laminin in the synovial intimal layer: An immunohistochemical study

The distribution of type IV collagen and laminin in the intimal layer of rheumatoid, osteoarthritic, traumatic and normal human synovium was determined by immunohistochemistry using polyclonal and monoclonal antibodies. All samples showed a similar pattern of labelling with type IV collagen and laminin present around the synovial intimal cells. Type IV collagen has previously only been identified in association with basement membranes which are not found at this site. Two major basement membrane components around synovial cells suggest the formation of a modified basement membrane-like structure.

Synovial chondromatosis of the temporomandibular joint: A light and electron microscopic study

The light and electron microscopic features of synovial chondromatosis of the temporomandibular joint of one patient are presented. The affected synovial membrane and the cartilaginous nodules, which were freely movable in the joint space as well as attached to or incorporated in the synovial membrane, were examined. Light microscopic observation revealed metaplastic formation of these nodules within the subintima of the synovial membrane. Different stages of development of the nodules were observable. Electron microscopic examination of the cartilaginous nodules revealed features of mature chondrocytes well endowed with rough-surfaced endoplasmic reticulum and Golgi apparatus. The synovial intimal cells had a differentiated ultrastructural appearance. Several cytoplasmic organelles of the chondrocytes and intimal cells are described. The results of this study support the benign nature of synovial chondromatosis.

Macrophage ferritin and iron deposition in the rat air pouch model of inflammatory synovitis.

Using a rat air pouch model of red cell promoted allergic inflammation, we have investigated the relation between ferritin synthesis and iron deposition in pouch wall lining cells. These cells have structural and immunohistochemical similarities to human synovial intimal cells and studies of them are pertinent to the clinical situation. In control air pouch wall tissue after single or double antigenic challenge the (apo)ferritin containing macrophages are most numerous seven days after antigenic challenge when there is active connective tissue proliferation and a generalised mononuclear cell response in the pouch wall, suggesting that (apo)ferritin is produced in macrophages as part of the tissue inflammatory response. In contrast with control tissue, where there is a steady decrease in positive cells over the ensuing weeks, injection of blood into both single and double challenge air pouches produces a significant (p less than 0.001) and continuing rise in the numbers of ferritin containing macrophages after day 7. Also, after 14 days Perls' positive ferric iron is detectable in increasing numbers of ferritin containing macrophages, a trend which is more marked in double challenge, blood injected air pouches. The histological data clearly show that there is a close relation between the presence of Perls' iron and proliferation of vascular and connective tissue elements in the pouch wall. We propose that this proinflammatory role of iron is the result of its ability to promote oxidative damage in tissues, and discuss ways in which this may take place.

Fibronectin production by synovial intimal cells.

The distribution of fibronectin in the inflamed synovium has been described previously using immunohistochemical methods. Under favourable conditions, it is possible to demonstrate apparent cytoplasmic staining of the intimal cell layer. We have further investigated the localisation of fibronectin in the synovial intimal cells using higher resolution techniques with peroxidase-antiperoxidase staining and high power light microscopy of semi-thin Araldite sections and immunoelectron microscopy using a protein A-gold technique. Synovia from 11 mechanical/traumatic, or osteoarthritic joints; 12 seropositive rheumatoid arthritis and nine cases from other joint diseases made a total of 32 cases examined in semi-thin sections, while six rheumatoid and two osteoarthritis synovia were studied by immunoelectron microscopy. Fibronectin was demonstrated in individual cells of the synovial intimal layer in 22 out of 32 samples examined by the light microscope method, and electron microscopy of adjacent sections showed that the positively staining cells were type B synoviocytes. Immunoelectron microscopy confirmed the presence of fibronectin within the rough endoplasmic reticulum of type B synoviocytes in all but one of the eight samples examined. The results provide evidence that the type B synoviocyte is responsible for fibronectin production.

Uraniosomes produced in the synovial membrane by uranyl acetate

Uranyl acetate was injected into the rabbit knee joint. This produced single-membrane-bound presumably lysosmal bodies (called 'uraniosomes') containing electron-dense crystals in Type A and Type B synovial intimal cells, subsynovial macrophages and lipocytes. Uranium deposits were also seen in the extracellular matrix. All uraniosomes and extracellular deposits analysed by electron-probe X-ray analysis were found to contain uranium, potassium and phosphorus. Traces of calcium and sulphur were also found in some of the uraniosomes and extracellular uranium deposits.

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.

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.

Long-term effects of myochrysine on the synovial membrane and aurosomes.

Mysochrysine injected into the rabbit knee joint produced regressive and destructive changes in the synovial membrane, ultimately leading to fibrosis. Aurosomes, containing characteristic electron-dense deposits indicating the presence of gold, formed in the synovial intimal cells and subsynovial macrophages. The number of aurosomes decreased with the passage of time but some were found even 2 yr after the injection of Myochrysine. Electron-probe X-ray analysis showed that the aurosomes contain gold, sulphur and phosphorus. A comparison was made between the atomic ratios of these elements in 3-day and 18-mth-old aurosomes but no significant difference was detected.

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.

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.

Nuclear fibrous lamina in pathological human synovial membrane

The synovial membrane from a patient with multiple sclerosis, psoriasis and arthritis was examined with the electron microscope. A nuclear fibrous lamina much thicker than that known to occur in normal cells of vertebrates was found in the synovial intimal cells and in subsynovial fibroblasts of this patient. Since such a thickened lamina has also been found in repair tissue in articular cartilage it is thought that thickening of the lamina may be related to the process of hyperplasia and repair.