Ultrastructure of the mouse synovial membrane. Development and organization of the extracellular matrix

Macrophage polarization in rheumatoid arthritis: signaling pathways, metabolic reprogramming, and crosstalk with synovial fibroblasts

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by persistent synovial inflammation and progressive joint destruction. Macrophages are key effector cells that play a central role in RA pathogenesis through their ability to polarize into distinct functional phenotypes. An imbalance favoring pro-inflammatory M1 macrophages over anti-inflammatory M2 macrophages disrupts immune homeostasis and exacerbates joint inflammation. Multiple signaling pathways, including Notch, JAK/STAT, NF-κb, and MAPK, regulate macrophage polarization towards the M1 phenotype in RA. Metabolic reprogramming also contributes to this process, with M1 macrophages prioritizing glycolysis while M2 macrophages utilize oxidative phosphorylation. Redressing this imbalance by modulating macrophage polarization and metabolic state represents a promising therapeutic strategy. Furthermore, complex bidirectional interactions exist between synovial macrophages and fibroblast-like synoviocytes (FLS), forming a self-perpetuating inflammatory loop. Macrophage-derived factors promote aggressive phenotypes in FLS, while FLS-secreted mediators contribute to aberrant macrophage activation. Elucidating the signaling networks governing macrophage polarization, metabolic adaptations, and crosstalk with FLS is crucial to developing targeted therapies that can restore immune homeostasis and mitigate joint pathology in RA.

Role of glucose metabolism in aggressive phenotype of fibroblast-like synoviocytes: Latest evidence and therapeutic approaches in rheumatoid arthritis

Glucose metabolism is considerably increased in inflamed joints of rheumatoid arthritis (RA) patients at early stages. Fibroblast-like synoviocytes (FLSs) activation and subsequent joint damage are linked with metabolic alterations, especially glucose metabolism. It has been shown that glucose metabolism is elevated in aggressive phenotype of FLS cells. In this regard, glycolytic blockers are able to reduce aggressiveness of the FLS cells resulting in decreased joint damage in various arthritis models. Besides, metabolic changes in immune and non-immune cells such as FLS can provide important targets for therapeutic intervention. Glycolytic enzymes such as hexokinase 2 (HK2), phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFKFB), and phosphoglycerate kinase (PGK) play essential roles in aggressive behavior of FLS cells. It has been documented that the HK2 enzyme is significantly upregulated in RA FLS cells, compared with osteoarthritis (OA) FLS cells. The HK2 is expressed in a few tissues and upregulated in the inflamed synovium of RA patients that makes it a potential target for RA treatment. Furthermore, HK2 has different roles in each cellular compartment, which offers another level of specificity and provides a specific target to reduce deleterious effects of inhibiting the enzyme in RA without affecting glycolysis in normal cells. Thus, targeting the HK2 enzyme might be an attractive potential selective target for arthritis therapy and safer than global glycolysis inhibition. Therefore, this review was aimed to summarize the current knowledge about glucose metabolism of FLS cells and suggest novel biomarkers, which are potential candidates for RA treatment.

Implication of HYBID (Hyaluronan-Binding Protein Involved in Hyaluronan Depolymerization) in Hyaluronan Degradation by Synovial Fibroblasts in Patients with Knee Osteoarthritis

Cell migration-inducing hyaluronidase 1 (CEMIP), also known as hyaluronan (HA)-binding protein involved in HA depolymerization (HYBID), plays a role in HA degradation. CEMIP2, also known as transmembrane protein 2 (TMEM2), possessing a sequence similarity with HYBID, is reported as a hyaluronidase in mice. However, the expression of these molecules in osteoarthritic synovium and their involvement in HA degradation in synovial fluid (SF) from patients with knee osteoarthritis remain elusive. This study examined their expression in synovial tissue and the relationship with molecular weight of HA in SF in knee osteoarthritis patients. Quantification of mRNA demonstrated that HYBID expression is significantly (5.5-fold) higher in osteoarthritic synovium than in normal control synovium, whereas TMEM2 expression level is similar between the two groups. By immunohistochemistry, HYBID was localized mainly to CD68-negative and fibroblast-specific protein 1-positive synovial lining cells and sublining fibroblasts in osteoarthritic synovium. The mRNA expression levels of HYBID, but not TMEM2, in osteoarthritic synovium positively correlated with distribution of lower-molecular-weight HA with below 1000 kDa in SF. HA-degrading activity in osteoarthritic synovial fibroblasts was abrogated by siRNA-mediated knockdown of HYBID. Among the 12 factors examined, IL-6 significantly up-regulated the HYBID expression and HA-degrading activity in osteoarthritic synovial fibroblasts. These data suggest that HYBID overexpressed by IL-6-stimulated synovial fibroblasts is implicated in HA degradation in osteoarthritic synovium.

Evaluation of the effect of polyphenol of escin compared with ibuprofen and dexamethasone in synoviocyte model for osteoarthritis: an in vitro study

Osteoarthritis (OA) is a chronic degenerative joint disease with inflammatory component. It is associated with progressive histological alterations and disabling symptoms. Today, drugs such as glucocorticoids (GCs) and nonsteroidal anti-inflammatory drugs (NSIADs) are commonly employed for treatment of osteoarthritis, but have serious and life-threatening side effects. The aim of the current study is to evaluate the effects of escin on cyclooxygenase-2 (COX-2, isoform), inducible nitric oxide synthase (iNOS), interleukin-1β (IL-1β), interleukin-18 (IL-18), tumor necrosis factor-alpha (TNF-α), and nitric oxide (NO) (1), as well as prostaglandin E2 (PGE2) on inflammatory cells, similar osteoarthritis in synoviocytes, and monocytes/macrophages, and to compare it with dexamethasone (DEX) and ibuprofen (IBP). Synovial cells were isolated from synovial membrane of the radiocarpal joint cartilage of an 8-month-old Holstein cow. THP-1 cells were prepared from Pasteur Institute of Iran. Cells were cultivated and exposed to lipopolysaccharide (LPS) stimulation without, or in the presence of, DEX, IBP, or escin. The gene expressions of IL-1β, TNF-α, IL-18, COX-2, and iNOS were evaluated by real-time PCR. Concentrations of NO and PGE2 were measured by ELISA methods. Our cells secreted an increased amounts of IL-1β, TNF-α, IL-18, COX-2, iNOS, NO, and PGE2 in response to LPS stimulation in all conditions. Escin can quench the gene expression of COX-2, iNOS, IL-1β, IL-18, and TNF-α in synoviocyte cells and production of NO and PGE2 in monocyte/macrophage cells alike DEX and IBP. We can use from escin for the treatment of osteoarthritis as an anti-inflammatory agent in the latter but further studies to support the results from such a model are needed.

Morphological evidence of telocytes in human synovium

A new cell type named telocyte (i.e. cell with distinctive prolongations called telopodes) has recently been identified in the stroma of various organs in humans. However, no study has yet reported the existence of telocytes in the synovial membrane of diarthrodial joints. This work was therefore undertaken to search for telocytes in the normal human synovium using transmission electron microscopy, immunohistochemistry and immunofluorescence. Ultrastructural analyses demonstrated the presence of numerous spindle-shaped telocytes in the whole synovial sublining layer. Synovial telocytes exhibited very long and thin moniliform telopodes and were particularly concentrated at the boundary between the lining and sublining layers and around blood vessels. Light microscopy confirmed the presence of CD34-positive telocytes in the aforementioned locations. Moreover, synovial telocytes coexpressed CD34 and platelet-derived growth factor receptor α. Double immunostaining further allowed to unequivocally differentiate synovial telocytes (CD34-positive/CD31-negative) from vascular endothelial cells (CD34-positive/CD31-positive). The in vitro examination of fibroblast-like synoviocyte primary cultures revealed the coexistence of different cell types, including CD34-positive telocytes projecting typical moniliform telopodes. In conclusion, our work provides the first evidence that telocytes do exist in the human synovium and lays the groundwork for future studies on synovial telocytes in a variety of degenerative and destructive joint diseases.

Fibroblast-like synoviocyte metabolism in the pathogenesis of rheumatoid arthritis

An increasing number of studies show how changes in intracellular metabolic pathways alter tumor and immune cell function. However, little information about metabolic changes in other cell types, including synovial fibroblasts, is available. In rheumatoid arthritis (RA), fibroblast-like synoviocytes (FLS) are the most common cell type at the pannus–cartilage junction and contribute to joint destruction through their production of cytokines, chemokines, and matrix-degrading molecules and by migrating and invading joint cartilage. In this review, we show that these cells differ from healthy synovial fibroblasts, not only in their marker expression, proto-oncogene expression, or their epigenetic changes, but also in their intracellular metabolism. These metabolic changes must occur due to the stressful microenvironment of inflamed tissues, where concentrations of crucial nutrients such as glucose, glutamine, and oxygen are spatially and temporally heterogeneous. In addition, these metabolic changes will increase metabolite exchange between fibroblast and other synovial cells, which can potentially be activated. Glucose and phospholipid metabolism as well as bioactive lipids, including sphingosine-1-phosphate and lysophosphatidic acid, among others, are involved in FLS activation. These metabolic changes likely contribute to FLS involvement in aspects of immune response initiation or abnormal immune responses and strongly contribute to joint destruction.

A synoviocyte model for osteoarthritis and rheumatoid arthritis: response to Ibuprofen, betamethasone, and ginger extract-a cross-sectional in vitro study

This study aimed at determining if synovial cell cultures from rheumatoid arthritis (RA), osteoarthritis (OA), and healthy controls (HC) differ and are suitable disease models in pharmacological studies, and tested their response to some anti-inflammatory drugs. Synovial cells were isolated from synovial membrane or joint fluid. Cells were cultivated and exposed to no or TNF-α stimulation without, or in the presence of, betamethasone, ibuprofen, or a standardized ginger extract. Concentrations of a panel of cytokines, growth factors, and chemokines were mapped for each culture and condition. Our cells secreted an increased amount of the cytokines IL-1β, IL-6, and IL-8 in response to TNF-α stimulation in all conditions. OA cells showed a higher IL-6 and IL-8 and a lower IL-1β production, when not stimulated, than RA and HC cells, which were similar. TNF-α stimulation caused similar IL-1β, IL-6, and IL-8 release in all groups. Ibuprofen showed no effect on cytokine production, while ginger extract was similar to betamethasone. Ginger extract was as effective an anti-inflammatory agent as betamethasone in this in vitro model. Cultured fibroblast-like synoviocytes from OA and RA subjects promise to be a useful pharmacological disease model, but further studies, to support results from such a model are needed.

Localization of CD44 and hyaluronan in the synovial membrane of the rat temporomandibular joint

Previous studies have pointed out a lack of adhesion structures in the synovial lining layer of the rat temporomandibular joint (TMJ) despite showing an epithelial arrangement. CD44, a major cell adhesion molecule, plays crucial roles as an anchor between cells and extracellular matrices by binding hyaluronan (HA) for the development of organs or the metastasis of tumors. The present study examined the localization of CD44 in the synovial membrane of the rat TMJ by immunocytochemistry for OX50, ED1, and Hsp25, which are markers for the rat CD44, macrophage-like type A, and fibroblast-like type B synoviocytes, respectively. Histochemistry for HA-binding protein (HABP) was also employed for the detection of HA. OX50 immunoreactions were found along the cell surface and, in particular, accumulated along the surface of the articular cavity. Observations by a double immunostaining and immunoelectron microscopy revealed that all the OX50-immunopositive cells were categorized as fibroblastic type B cells, which had many caveolae and a few vesicles reactive to intense OX50. However, the macrophage-like type A cells did not have any OX50 immunoreaction in the synovial lining layer. A strong HABP reaction was discernable in the extracellular matrix surrounding both OX50-positive and -negative cells in the synovial lining layers, exhibiting a meshwork distribution, but weak in its sublining layer. This localization pattern of CD44 and HABP might be involved in the formation of the epithelial arrangement of the synovial lining layer. Furthermore, OX50 immunonegativity in the type A cells suggests their low phagocytotic activity in the rat TMJ under normal conditions.

Development of the articular cavity in the rat temporomandibular joint with special reference to the behavior of endothelial cells and macrophages

Previous developmental studies on the temporomandibular joint (TMJ) have proposed several hypotheses on the formation of its articular cavity. However, detailed information is meager. The present study examined the formation process of the articular cavity in the rat TMJ by immunocytochemistry for CD31, RECA-1, and ED1, which are useful cellular markers for endothelial cells and monocyte/macrophage lineages, respectively. The upper articular cavity formation had begun by embryonic day 21 (E21) and was completed at postnatal day 1 (P1) in advance of the lower cavitation; the latter took place from P1 to P3. The occurrence and distribution pattern of the CD31-, RECA-1-, and ED1-positive cells differed between the upper and lower articular cavity-forming areas: the ED1-positive cells exclusively occurred in the area of the prospective upper articular cavity prior to its formation, while no ED1-positive cell appeared in the lower cavity-forming area. In contrast, the CD31- and RECA-1-positive endothelial cells were restricted to the lower cavity-forming area (never the prospective upper cavity) at E19 and diminished thereafter. Throughout the cavity formation, we failed to find any apoptotic cells in the cavity formation area, indicating no involvement of apoptosis in the cavity formation in TMJ. The present findings on the behaviors of endothelial cells and ED1-positive cells show a possibility of different mechanism in the cavity formation between the upper and lower articular cavities in the rat TMJ. The appearance of ED1-reactive cells and temporal vascularization may play crucial roles in the upper and lower articular cavity formation, respectively.

Development of the synovial membrane in the rat temporomandibular joint as demonstrated by immunocytochemistry for heat shock protein 25

The synovial lining layer of the temporomandibular joint (TMJ) consists of macrophage-like type A cells and fibroblast-like type B cells. Until now, little information has been available on the development of the synovial membrane in TMJ. In the present study we examined the development of the synovial lining layer in the rat TMJ by light- and electron-microscopic immunocytochemistry for heat shock protein (Hsp) 25, which is a useful marker for type B cells. At embryonic day 19 (E19), a few Hsp25-positive cells first appeared in the upper portion of the developing condyle. During the formation of the upper articular cavity (E21 to postnatal day 1 (P1)), a few positive cells were arranged on its surface. Immunoelectron microscopy demonstrated that these cells had ultrastructural features of fibroblast-like type B cells. In addition, some Hsp25-positive cells moved to the deep portion by extending their cytoplasmic processes toward the articular cavity at P3. At that time, the presence of typical macrophage-like type A cells in the lining layer was confirmed by immunoelectron microscopy. The slender processes of Hsp25-positive cells showed a continuous covering with the synovial surface at P7, followed by a drastic increase in the Hsp25-positive cells at P15 and later, when active jaw movement occurred. These findings suggested that the arrangement and morphological maturation of type B cells are closely related to the formation of the articular cavity in the embryonic period and the commencement of active jaw movement after birth, respectively.

Ultrastructural localization of hyaluronic acid in the synovium of the goat knee joint

In the Japanese miniature (Shiba) goat, the synovial membrane contains synoviocytes referred to as type A (macrophage-like cells) and type B cells (fibroblast-like cells) in the intimal layer. Small capillaries and blood vessels of varying sizes were located in the extracellular matrix in the synovial subintima. The type A cells in the synovium possessed numerous vesicles, vacuoles and lysosomes as well as pinocytotic vesicles. These ultrastructural features indicating phagocytosis showed distinct positive reactions following hyaluronan staining. On the other hand, in the type B cells, hyaluronic acids were present in the surface coat of the plasma membrane and its periphery. Additionally, perivascular connective tissue of the small capillaries and blood vessels and interfibrous matrix contained hyaluronan. The results suggest that hyaluronic acid, in the synovial tissue, is synthesized on the plasma membrane of type B cells, and taken up by type A cells. Moreover, hyaluronan is involved in cellular functions in the synovial connective tissue.

Synovial membrane in the temporomandibular joint--its morphology, function and development

This paper reviews recent findings of the synovial membrane, in particular the morphology, function and development of synovial lining cells, in the temporomandibular joint (TMJ). Electron microscopic studies have confirmed the synovial membrane in TMJ consists of macrophage-like type A cells and fibroblast-like type B cells identical to those in other systematic joints. The macrophage-like type A cells react with anti-macrophage and macrophage-derived substances including the major histocompatibility class II molecule, and show a drastic increase in their number in the inflamed synovial membrane. In addition, they have the ability to produce substances involved in the progression of TMJ inflammation such as nitric oxide and inducible nitric oxide synthase. Observation of osteopetrotic mice revealed that macrophage-like type A cells in TMJ are derived from monocyte lineage. Immunocytochemistry for 25kDa heat shock protein was able to depict the entire shape of fibroblast-like type B cells including their unique processes. The expression of an estrogen receptor alpha-immunoreaction in the fibroblast-like type B cells may explain the etiology of temporomandibular disorders at a higher frequency in females than in males, suggesting that TMJ is a target tissue for estrogen. Furthermore, fibroblast-like type B cells are equipped with a basement membrane to serve as an adhesion molecule for the fibroblast-like type B cells to keep their epithelial arrangement. A clear understanding of the morphology of the intact synovial membrane will serve to clarify the etiology and development of temporomandibular disorders.

Ultracytochemical demonstration of glycoproteins in the canine knee synovium

By various ultracytochemical methods, glycoconjugates of the synoviocytes, the intercellular matrix and the wall of the small capillaries were studied in the synovial intimal tissues of the canine knee joint. Glycoconjugates with vicinal diol groups could be visualized in certain elements of the Golgi complex, lysosomes, vacuoles, the majority of intracellular cytomembranes, the surface coat of the plasma membrane and glycogen particles in type A cells. In type B cells, less-developed Golgi complexes, and fewer lysosomes and vacuoles were present in the cytoplasm than in that of type A cells. In contrast, a large number of cytoplasmic glycogen particles and abundant vicinal diol-containing groups in the surface coat of the plasma membrane became especially obvious in the B cells. Abundant neutral and acidic glycoproteins were observed in fibrous components in the intercellular matrix. In the small capillaries, strongly positive staining intensities for neutral and acidic glycoconjugates were observed in the basement membrane and perivascular connective tissue, as well as in the surface coat of the luminal plasma membrane of the endothelial cells, although to a somewhat weaker degree. Sialic acid, particularly, was notable in the surface coat of the latter cells. In addition, glycoproteins in the type A cells were shown by lectin ultracytochemistry to contain a variety of saccharide residues such as alpha-D-mannose, alpha-D-glucose, alpha-L-fucose, N-acetyl-beta-D-glucosamine, and N-acetyl-neuraminic acid, which were also found in the plasma membrane of the B cells. The properties of the glycoconjugates found are discussed in relation to the basic functions assigned to the synovial membrane of the canine knee joint.

Ultracytochemistry of glycosaminoglycans in the canine knee synovium

The accurate localization and nature of glycosaminoglycans (GAGs) in the canine knee synovium were studied by ultracytochemical methods that involved high or low iron diamine-thiocarbohydrazide-silver proteinate (physical development) staining in combination with enzyme digestion control procedures. The results obtained indicated that heparan sulfates and hyaluronan were present mainly in the plasma membrane of the B (fibroblast-like) cells. In contrast, the plasma membrane of the A (macrophage-like) cells showed negative reactions after the histochemical examination. Dermatan sulfates, chondroitin sulfates (A and/or C) and hyaluronan were localized in the extracellular matrix of the synovial intima, whereby dermatan sulfates were confined to the fibrous component, whereas chondroitin sulfates and hyaluronan were found in the interfibrous matrix. Heparan sulfate was the only notable GAG molecular species localized in the basement membrane of the capillary wall. It is obvious that differences in the quality and localization of glycosaminoglycans in the canine synovial tissue are of specific interest in understanding normal functions as well as pathological alterations of the knee synovium in mammals.

Histochemical analyses of glycosaminoglycans in the synovial membrane of the canine knee joint

The accurate localization and nature of glycosaminoglycans in the synovial membrane of the canine knee joint were examined histochemically by means of the selective sensitized diamine procedures based upon high and low iron diamine stainings in combination with enzyme digestions. Using these methods, it was possible to clearly and easily detect exceedingly small amounts of glycosaminoglycans in synovial tissues, which cannot be visualized by methods employed to date. The sensitized high iron diamine (S-HID) procedure resulted in positive reactions of varying intensities in the intercellular matrix of synovial intima, and in the extracellular matrix and small capillary walls of the superficial layer in the synovial subintima, and also reacted vividly in the extracellular matrix and blood vessel walls of the deeper layer in the synovial subintima. In particular, the sensitized low iron diamine (S-LID) procedure resulted in positive reactions of the extracellular matrix in the synovial subintimal layers. The S-HID and S-LID procedures combined with the enzyme digestions proved that glycosaminoglycan molecular species such as chondroitin sulfate A/C, dermatan sulfate, heparan sulfate and hyaluronic acid are present in various concentrations in the synovial membrane of the canine knee joint. The present results were discussed with reference to the histophysiological and pathophysiological functions of glycosaminoglycans in the synovium of domestic mammals.

In vitro loading of human synovial membrane with 5-hydroxydopamine: evidence for dense core secretory granules in type B cells

Ultrastructural studies of the synovial membrane were performed on tissue samples obtained from the human lumbar facet joint. Ultrastructural changes in synoviocytes were studied after loading synovial samples with 5-hydroxydopamine (5-OHDA) in an oxygenated Krebs' solution, prior to fixation. Synoviocytes were set loosely in the intimal matrix and classified into type A (phagocytic) and type B (secretory) cells. In general, type A cells populated the surface of the synovial lining, whereas type B cells were located deeper in the tissue, extending a process into the synovial fluid. Type B cells in control samples contained sparse secretory granules. Free nerve endings were not found in the synovial intima. In response to incubation in 5-OHDA, a precursor of biogenic monoamines, synoviocytes clustered and established contact. The ultrastructure of type B cells in the loaded group clearly differed from controls. They possessed typical membrane-bound vesicles, containing an electron dense interior surrounded by a lucent space. The size of these dense core vesicles ranged from 100 to 260 nm (on average 180 nm). They were in relation to microtubules and located preferentially in the marginal area of the cytoplasm, close to the Golgi complex. The ultrastructure of type A cells was not significantly altered. The present observations provide morphological evidence for the amine-handling properties of type B cells, indicating that they might be added to the list of 'APUD' cells of the diffuse neuroendocrine system. A recepto-secretory function for type B cells is discussed.

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.

Three-dimensional ultrastructure of synoviocytes in the horse joint as revealed by the scanning electron microscope

The synovial membrane displays a superficial cellular lining composed of two types of synoviocytes: "absorptive" macrophages (type A cells) and "secretory" fibroblast-like cells (type B cells). The types are intermingled and extend a variety of processes, rendering the cellular architecture of the synovial membrane difficult to visualize. Previous electron microscopic and histochemical studies failed to demonstrate the entire shape of synoviocytes, except our immunohistochemical study for protein gene product 9.5 in the horse joint. The present SEM study is the first to demonstrate the three-dimensional ultrastructure of synoviocytes as well as their distribution in the synovial membrane, using macerated samples from the horse carpal joints. The equine synovial membrane was largely covered by conspicuously developed synovial villi. Type A synoviocytes were closely similar to macrophages in regard to surface structure, and showed uneven distribution with the densest occurrence around the tips of the synovial villi. In the basal half of villi, type B synoviocytes, which were situated in close proximity to the synovial cavity, projected thick processes horizontally and intertwined to form a regular network of processes on the synovial surface. Those in the upper half of the villi were located in the abluminal layers and protruded an antenna-like process into the joint cavity with tips covered with long microvilli, in addition to forming the superficial plexus of processes. Type B cells were also provided with fine, membranous extensions that tended to cover the surface of synovial intima. The meshwork of horizontal processes, the antenna-like processes, and the membranous processes imply advantages in not only secretion but also sensation and regulation of the barrier function in the synovial membrane.

Effect of depletion of interstitial hyaluronan on hydraulic conductance in rabbit knee synovium

1. The hydraulic resistance of the synovial lining to fluid outflow from a joint cavity (Qs) is important for the retention of intra-articular lubricant. The resistance has been attributed in part to extracellular glycosaminoglycans, including hyaluronan and chondroitin sulphates. Increased permeability in joints infused with testicular hyaluronidase, which digests both chondroitin sulphates and hyaluronan, supports this view. In this study the importance of interstitial hyaluronan per se was assessed using leech and Streptomyces hyaluronidases, which degrade only hyaluronan. 2. Ringer solution was infused into the knee joint cavity of anaesthetized rabbits for 30 min, with or without hyaluronidase, after which intra-articular pressure (Pj) was raised and the relation between pressure and outflow determined. 3. Treatment with Streptomyces, leech or testicular hyaluronidases increased the fluid escape rates by similar factors, namely 4- to 6-fold. After Streptomyces hyaluronidase treatment the slope d 8d s/dPj, which at low pressures represents synovial hydraulic conductance, increased from a control of 0.90 +/- 0.20 microl min-1 cmH2O-1 (mean +/- s.e.m. , n = 6) to 4.52 +/- 0.70 microl min-1 cmH2O-1. The slope d 8d s/dPj increased to a similar level after testicular hyaluronidase, namely to 4.14 +/- 1.06 microl min-1 cmH2O-1 (control, 0.54 +/- 0.24 microl min-1 cmH2O-1). Streptomyces and leech hyaluronidases were as effective as testicular hyaluronidase (no statistically significant differences) despite differences in substrate specificity. 4. It was shown using histochemical and immunohistochemical techniques that hyaluronan was removed from the synovium by leech, Streptomyces and testicular hyaluronidases. The binding of antibodies 2-B-6 and 3-B-3 showed that the core proteins of the chondroitin sulphate proteoglycans remained intact after treatment with hyaluronidases, and the binding of 5-D-4 showed that keratan sulphate was unaffected. An azocasein digestion assay confirmed that the hyaluronidase preparations had no significant proteolytic activity. 5. The effect of the hyaluronidases was four times greater than predicted from the low concentration of interstitial hyaluronan and its resistivity. Factors that might amplify the effect of hyaluronan depletion include the matrix-organizing role of hyaluronan, and/or non-uniformity of hyaluronan distribution. It is concluded that interstitial hyaluronan makes a major contribution to synovial hydraulic resistance, but the mechanisms are as yet poorly understood.

Glycosaminoglycan concentration in synovium and other tissues of rabbit knee in relation to synovial hydraulic resistance

1. The hydraulic resistance of the synovial lining of a joint, a key coupling coefficient in synovial fluid turnover, is thought to depend on the concentration of biopolymers (glycosaminoglycans (GAGs) and collagen) in the synovial intercellular spaces, because these polymers create hydraulic drag. The primary aim of this study was to obtain microscopically separated, milligram samples of the very thin synovium from eight rabbit knees, and to analyse these quantitatively for GAGs (chondroitin sulphate, heparan sulphate and hyaluronan) and collagen to allow comparison with published hydraulic resistance data. Synovial fluid and femoral cartilage were also studied. 2. Synovium comprised 73 +/- 3% water by weight (mean +/- S.E.M.). Of the 270 mg solid per gram of wet tissue, protein formed 136 mg (by automated amino acid analysis), and of this 94 mg was collagen by hydroxyproline analysis. From the collagen mass and fibril volume fraction (0.153 of tissue by morphometry), fibrillar specific volume was calculated to be 1.43 ml per gram of molecular collagen, and fibril water content 47% by volume. 3. The concentration of chondroitin 4-sulphate (C4S) plus chondroitin 6-sulphate (C6S), measured by capillary zone electrophoresis was 0.55 mg per gram of synovium--much greater than in synovial fluid (0.04 mg g-1) and much less than in cartilage (27.8 mg g-1). The C4S/C6S ratio in synovium (7.3) differed from that in cartilage (0.7), indicating that different proteoglycans predominated in synovium. The heparan sulphate concentration, assayed by radioactive Ruthenium Red binding, was 0.92 mg per gram of synovium (synovial fluid, 0.08 mg g-1; cartilage, 0.72 mg g-1). 4. In contrast to sulphated GAGs, the hyaluronan concentration was highest in synovial fluid (3.53 mg g-1; biotinylated G1 domain binding assay). The concentration in synovial interstitium was only 0.56 mg g-1 (corrected for interstitial volume fraction, 0.66), even though there is open contact between synovial interstitium and synovial fluid. This may be due to exclusion or washout. 5. Total GAG mass was approximately 4 mg per gram of synovial interstitium. A model of trans-synovial flow indicated that a uniform GAG concentration of 4 mg g-1 is less than 1/3rd of that required to explain the experimental estimate of synovial hydraulic resistance. Errors in the resistance estimate do not appear to be large enough to resolve the problem. It is possible, therefore, that additional polymeric material in the interstitium, such as glycoproteins and proteoglycan core protein, may contribute to the hydraulic resistance.

Radial organization of interstitial exchange pathway and influence of collagen in synovium

The synovial intercellular space is the path by which water, nutrients, cytokines, and macromolecules enter and leave the joint cavity. In this study two structural factors influencing synovial permeability were quantified by morphometry (Delesse's principle) of synovial electronmicrographs (rabbit knee), namely interstitial volume fraction Vv.1 and the fraction of the interstitium obstructed by collagen fibrils. Mean Vv.1 across the full thickness was 0.66 +/- 0.03 SEM (n = 11); but Vv.1 actually varied systematically with depth normal to the surface, increasing nonlinearly from 0.40 +/- 0.04 (n = 5 joints) near the free surface to 0.92 +/- 0.02 near the subsynovial interface. Tending to offset this increase in transport space, however, the space "blocked" by collagen fibrils also increased nonlinearly with depth. Bundles of collagen fibrils occupied 13.6 +/- 2.4% of interstitial volume close to the free surface but 49 +/- 4.8% near the subsynovial surface (full-thickness average, 40.5 +/- 3.5%), with fibrils accounting for 48.6-57.1% of the bundle space. Because of the two counteracting compositional gradients, the space available for fibril-excluded transport (hydraulic flow and macromolecular diffusion) was relatively constant > 4 microns below the surface but constricted at the synovium-cavity interface. The space available to extracellular polymers was only 51-53% of tissue volume, raising their effective concentration and hence the lining's resistance to flow and ability to confine the synovial fluid.

Type VI collagen-specific messenger RNA is expressed constitutively by cultured human synovial fibroblasts and is suppressed by interleukin-1

OBJECTIVE

Type VI collagen is a prominent constituent of the synovial extracellular matrix. The cellular source of this matrix protein and the identity of local factor sin synovium that may regulate its expression have not been delineated, however. We examined the capacity of human fibroblast-like synovial cells to synthesize type VI collagen as well as the effect of interleukin-1 (IL-1) on this expression.

METHODS

RNA was extracted from cultured human synovial cells derived from patients with rheumatoid arthritis (RA) and osteoarthritis (OA). Northern blots were analyzed using sequence-specific probes, and steady-state messenger RNA (mRNA) levels of the 3 alpha (VI) procollagen chains were measured. The effect of IL-1 treatment on these levels was determined.

RESULTS

Abundant expression of 3 characteristic mRNA transcripts, corresponding to the alpha 1 (4.2-kb), alpha 2 (3.5-kb), and alpha 3 (8.5-kb) chains of type VI procollagen, was observed in untreated cells derived from RA and OA patients. IL-1 treatment consistently suppressed steady-state mRNA levels for all 3 alpha (VI) procollagen chains in a time- and dose-dependent manner. Tumor necrosis factor alpha induced a response similar to that of IL-1, while IL-2 was ineffective in this regard. Indomethacin partially restored alpha (VI) mRNA expression in IL-1--treated cells.

CONCLUSION

These studies provide novel data demonstrating abundant steady-state levels of mRNA transcripts coding for all 3 type VI procollagen polypeptides in human synovial fibroblast-like cells, as well as coordinated down-regulation of these transcripts by IL-1. Local production of IL-1 may thus constitute an important means in vivo of regulating the production of type VI collagen.

Morphogenesis and origin of fibrous long-spacing collagen fibers in collagenase-treated mouse skin tissues

Morphogenesis and origin of fibrous long-spacing collagen (FLS) fibers in newborn mouse skin tissues treated with collagenase were examined using ultrastructural observation, morphometry, histochemical methods, and immunoelectron microscopy. The enzyme caused both the partial destruction of basal laminae and the formation of abundant FLS fibers in the dermal matrix. The fibers were usually distributed in the vicinity of basal laminae in the capillaries or basal layer cells. The fibers were characterized by the cross-striated dark bands with about 91 nm periodicity and longitudinally aligned filaments with a diameter of about 6.5 nm. The dark bands of FLS fibers were often continuous with the basal laminae. Histochemical results showed that the dark bands contained the similar mucopolysaccharides which were involved in the basal laminae. Immunoelectron microscopic results showed that laminin was present in the dark bands as well as in the basal laminae, and that type VI collagen was located in the filaments of FLS fibers. These results suggest that the dark bands are formed by products similar to basal laminae and that the products were precipitated on type VI collagen-contained filaments with periodic intervals of about 91 nm. Morphometric examination revealed that there was no differences in ultrastructure between FLS fibers of a collagenase-treated mouse and those of a human neural tumor.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Immunohistochemical study of extracellular material in the aged human synovial membrane

Types III, IV, VI collagen and laminin distribution in synovial tissue of seven autopsy knee joints from old human donors (69-94 years of age) were investigated with immunocytochemical and immunohistochemical methods. The synovial intima is separated from the subintimal tissue by an intermediate fibrillar zone rich in staining for type III collagen. In the intima basement membrane-like material associated with synovial lining cells stains for type IV collagen and laminin. Fine fibrils surrounding the lining cells stain for type VI collagen. In two of the cases type VI collagen occurs mainly as long-spacing collagen, the distinct aggregated form of type VI collagen. This staining pattern was qualitatively the same in all different regions and cases investigated. However, considerable quantitative differences were seen.

Morphology of the synovium during its differentiation and development in the mouse knee joint. A histochemical, SEM and TEM study

The prenatal and postnatal development of the mouse knee joint was investigated by transmission and scanning electron microscopy. In the prenatal stage, following the appearance of a narrow intercellular cleft between two skeletal elements on the 16th fetal day, clefting extended into the lateral synovial mesenchyme. In some regions, the extension of the cleft was very rapid, but in a certain region (future fat pad region), it was somewhat slower. Macrophage-like cells appeared in the synovial mesenchyme on the 16th fetal day, and then increased in number, and were distributed as if they were clustering around the presumptive clefting zone in the future fat pad region on the 17th-18th fetal day. This suggests that macrophage-like cells may participate in joint development, as they phagocytize and remove some kinds of solid extracellular matrix, and facilitate the cleft extension. In the early postnatal stage, scanning electron microscopic observations showed that there were two different types of cell in the synovial lining. One of them exhibited a surface morphology corresponding to that of macrophages: a spherical cell body and numerous pseudopodia. The other type of cell exhibited various cell shapes with many cytoplasmic processes extending along the synovial surface.

Immunohistochemical demonstration of collagenase and tissue inhibitor of metalloproteinases (TIMP) in synovial lining cells of rheumatoid synovium

Degradation of fibrillar collagens is a central process in joint destruction in rheumatoid arthritis. Collagenase responsible for the collagenolysis has been immunolocalized on the extracellular matrix components at the cartilage/pannus junction in the rheumatoid joint, but very little is known about cellular source of the proteinase. In this paper monospecific antibodies against collagenase and tissue inhibitor of metalloproteinases (TIMP) were applied to rheumatoid and normal synovium to identify cells synthesizing and secreting the enzyme and its inhibitor. By treating the specimens with the monovalent ionophore, monensin, both collagenase and TIMP could be immunolocalized in hyperplastic synovial lining cells in rheumatoid synovium, but not in the cells of normal synovium. Dual immunolocalization studies demonstrated that the majority of the lining cells (approximately 64%) produce both collagenase and TIMP, while approximately 3% of the cells were positive only for collagenase, and 11% only for TIMP. Neither collagenase nor TIMP was immunolocalized on the extracellular matrix components in the synovia examined. These data suggest that synovial lining cells in rheumatoid arthritis secrete both collagenase and TIMP into the joint cavity. The role of collagenase in joint destruction in rheumatoid arthritis is discussed with reference to the regulation of the activity by TIMP.

Ontogenetic development of synovial A cells in fetal and neonatal rat knee joints

Ontogenetic development of the synovial A cells in fetal rat knee joints was investigated by immunohistochemistry, immuno-electron microscopy, cultivation, and autoradiography. At day 17 of gestation, immature macrophages were first seen in the articular interzone, and thereafter they differentiated into macrophages (synovial A cells), which were found in the synovial intima. The degree of reactivity of macrophages with five monoclonal antibodies increased in the developing synovial membranes of fetal rats as shown by immunohistochemistry. Similar findings were obtained in organ cultures of fetal knee joints. A marked difference of proliferative potential was found between A and B cells during ontogeny. A cells after birth did not incorporate 3H-thymidine in contrast to B cells. Before birth, B cells had a labelling index which was at least five times larger than that of A cells. The results of this study indicate that the synovial A cells are derived from both monocytes and fetal macrophages circulating in peripheral blood and that they differ from the synovial B cells in morphology, differentiation, and proliferative potential.

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

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

Ultrastructure of transport pathways in stressed synovium of the knee in anaesthetized rabbits

1. The hydraulic conductance of the synovial lining of a rabbit knee increases greatly when intra-articular pressure (IAP) is raised above approximately 9 cmH2O (yield point). To investigate the cause, synovium was fixed in situ by perfusion at controlled IAP and prepared for transmission electron microscopy. Micrographs of synovium fixed below yield pressure (atmospheric pressure and 5 cmH2O IAP, ten joints) and above it (25 cmH2O IAP, five joints) were analysed by morphometry. 2. The discontinuous cellular lining consisted of fibroblast-like cells (67%) and macrophage-like cells (33%) separated by interstitium-filled gaps. Interstitium formed 26-36% of the surface below yield pressure. Depending on sample site the surface gaps averaged 1.9 +/- 0.2 to 2.4 +/- 0.2 microns wide below yield pressure (mean +/- S.E.M. throughout). Above yield pressure the mean gap width increased by 42-64% (P less than 0.05, analysis of variance). 3. The qualitative and quantitative composition of the lining varied with distance below the surface. In a plane 5 microns deep, the intercellular distances and interstitial area fraction were almost double those at the surface. Classic periodic collagen fibrils (diameter 50 +/- 3 nm) abounded at 5 microns depth whereas the surface interstitium was richer in Ruthenium Red-staining microfibrils (diameter 9.3 +/- 0.7 nm) associated with 93 nm period fibrous long-spacing bundles. 4. Averaging over all the tissue between the surface and the 5 microns deep plane, the mean interstitial volume fraction was 0.61 +/- 0.05 at 5 cmH2O and 0.67 +/- 0.02 at 25 cmH2O (n.s.). 5. Capillary fenestrae (8.5 +/- 1.1 per fenestrated profile) and intercellular junctions were unaltered at high IAP. The tortuosity of the capillary-to-joint cavity path was 1.50 +/- 0.01 below yield pressure and 1.86 +/- 0.24 at 25 cmH2O (n.s.). 6. Intra-articular tracers (ferrocyanide, ferritin and glycogen) permeated synovial interstitium without evidence of preferential pathways. Ferrocyanide delineated the capillary intercellular junction as a permeable channel. Ferritin and glycogen were phagocytosed by the macrophages. 7. In suprapatellar areolar synovium, the most extensive and most altered tissue, the ratio of interstitial area to path length increased maximally 4.1 times between 5 and 25 cmH2O IAP. This represents a substantial contribution to the physiologically estimated rise in interstitial conductance (14 x) but does not wholly explain it.

Human epidermal growth factor for the stratification of synovial lining layer and neovascularisation in rheumatoid arthritis

Immunohistochemical study showed selective localisation of human epidermal growth factor (hEGF) to the synovial lining layer. Although the synovial lining layer of the rheumatoid, osteoarthritic, and traumatic joints was hEGF positive, hEGF staining was especially dense at the rheumatoid synovial lining layer; the staining increasing linearly according to the degree of stratification of the lining layer (r = 1). Human epidermal growth factor was ultrastructurally localised to cytoplasm, especially to rough endoplasmic reticulum, of the synovial lining fibroblast-like (type B) cell. Only the cell surface of macrophage-like (type A) cells was hEGF positive. When different histological variables were compared with each other a positive correlation was found between hEGF staining of the synovial lining layer and the degree of neovascularisation of rheumatoid synovium (r = 0.72). Although some lymphocytes were weakly hEGF positive, neovascularisation did not correlate with the extent of lymphocyte infiltration or of hEGF staining of lymphocytes. Lymphocyte infiltration or hEGF staining of lymphocytes did not correlate with hEGF staining of the synovial lining layer, whereas the lymphocyte infiltration correlated positively with the extent of perivascular accumulation of lymphocytes (r = 0.89). These findings suggest that (a) hEGF is synthesised by and secreted through endoplasmic reticulum and Golgi apparatus from the synovial lining type B cell; (b) hEGF is at least partially responsible for the pathogenesis of stratification of the rheumatoid synovial lining layer, and perhaps of neovascularisation of the rheumatoid synovium, whereas it is not responsible for lymphocyte accumulation to the rheumatoid synovium.

The developmental anatomy of the equine navicular bursa and associated structures

The navicular bone, navicular bursa and their associated structures were collected from 20 horses ranging in age from 80 days gestation to 2 years post-gestation. The right front foot of every horse was sampled for light microscopy. The development of the navicular bursa and associated structures were studied. Study of the developmental anatomy of the equine navicular bursa established that the bursa is a distinct entity in both the fetus and the adult horse. Development of the bursal cavity in the fetus was found to be complete by 120 days of gestation. Synovial membrane of the navicular bursa was first evident at 100 days of fetal age. With increasing fetal maturation there was a concurrent development in the synovial membrane consisting of increased cellularity, vascularity and villi formation. Nerve fibers or nerve endings were not observed within the synovial membrane of the navicular bursa. However, nerve bundles were often observed within the associated connective tissue, bursal capsule and distal navicular ligament. Pacinian corpuscles were observed in the 200-day fetus in close proximity to the navicular bursa. The development of a fibrous bursal capsule was first evident at 160 days fetal age, thereafter increasing in both thickness and density. Ligaments of the navicular bone were found to develop early in fetal life. At 100 days the collateral sesamoidean ligaments were well developed; however earliest evidence of formation of the distal navicular ligament was at 120 days. In both the fetus and the adult the proximal blood supply to the navicular bone was found to course dorsally in close proximity to the collateral sesamoidean ligament to enter the proximal border of the navicular bone. Concurrent with weight bearing there was a dorsal palmar orientation of the bone trabeculae of the navicular bone. In the young postgestational horses a progressive roughening or fraying of the palmar surface of the navicular bone and the apposing surface of the deep digital flexor tendon was evident.

The immunohistology of synovial lining cells in normal and inflamed synovium

The immunohistology of synovial lining cells (SLCs) in normal and inflamed hyperplastic synovium was investigated using monoclonal antibodies directed against leucocyte common antigen (LCA) HLA-DR and other macrophage components. We found that some SLCs in normal synovium express LCA, HLA-DR, and monocyte/macrophage-associated antigens. The number of SLCs expressing these antigens is increased in hyperplastic osteoarthritic (OA) and rheumatoid (RA) synovium. Some SLCs which did not react for LCA or other macrophage markers but were positive for HLA-DR were also noted in normal synovium and some segments of hyperplastic OA synovium. SLCs which are positive for LCA, HLA-DR, and macrophage markers contribute to the intimal hyperplasia in RA where they account for the majority of SLCs in the synovial intima. In OA synovium, the distribution of SLCs showing this pattern of reactivity was less uniform with numerous SLCs which were positive for HLA-DR but negative for LCA and other macrophage markers also present in the synovial intima. These findings indicate that there are some SLCs of bone marrow origin in normal and hyperplastic synovium. They also suggest that recruitment of SLCs of marrow origin is important in the production of intimal hyperplasia in both RA and OA and that there is also a significant local proliferation of non-marrow derived SLCs in OA.

Pericardium of rodents: pores connect the pericardial and pleural cavities

Numerous circular fenestrations or pores were present in the pericardium of the rat, golden hamster, and mouse. The pericardial pores were most numerous in the mouse. They were usually less than 50 micron in diameter and situated in a meshwork formed by thick, wavy bundles of collagen fibers and thin, straight, elastic fibers. These pores directly connected the pericardial and pleural cavities and indirectly connected the right and left pleural cavities; i.e., the pericardial cavity in the rodents is not independent from but intercommunicates with the adjacent pleural cavities. There were many aggregates of free cells or milky spots in the pericardium. They principally consisted of lymphocytes, macrophages, and mast cells and were directly exposed to the pericardial cavity.

Pleomorphic adenoma with a predominantly myoepithelial proliferation of the vagina

A case of pleomorphic adenoma of the vagina in a 44-year-old woman was described. The tumor was a submucosal mass measuring 3.5 X 2 X 2 cm and located in the left lateral wall 1.5 cm inside the introitus. Histologically, it was predominantly composed of sheets and strands of spindle-shaped or polygonal cells focally dispersed in the myxoid tissue to form pseudomicrocysts. Ultrastructure demonstrated the basal lamina, desmosomes, variable amounts of filaments of both intermediate and microfilament, and occasionally microvilli in these tumor cells indicating that dominant cells were myoepithelial in nature. With immunohistochemical studies, keratin and cytokeratin were positive, whereas, S-100 protein, glial fibrillary acidic protein, vimentin, secretory component, and lysozyme were negative. The previously published cases were reviewed and compared with the present case.

Effect of fluid pressure on the hydraulic conductance of interstitium and fenestrated endothelium in the rabbit knee

A synovial cavity is separated from plasma by synovial intima in series with capillary endothelium. Because 20% of the intimal surface is bare interstitium, the system is a convenient model for the study of passive transport through serial endothelial and interstitial layers. Here hydraulic flow across the composite barrier was investigated in forty-seven knees of isolated, blood-perfused rabbit hindquarters, at intra-articular pressures between 4 and 30 cmH2O. In order to measure barrier conductance at constant intra-articular pressure, pressure on the opposite side of the barrier was varied, i.e. capillary blood pressure (PC). Capillary pressure was changed by alteration of vascular perfusion pressures, and the resulting changes in rate of absorption of Krebs solution from the synovial cavity (QS) were recorded. Trans-synovial absorption was a negative linear function of PC at each joint pressure, in verification of the applicability of Starling's hypothesis to this system. The hydraulic conductance of the blood-joint barrier was calculated as dQS/dPC. Conductance was independent of intra-articular pressure below 9 cmH2O and was 0.12 +/- 0.015 microliter min-1 mmHg-1 (mean +/- S.E. of mean). Barrier conductance increased as a curvilinear function of intra-articular pressure above 9.4 cmH2O (yield pressure). At 30 cmH2O conductance averaged 0.60 +/- 0.06 microliter min-1 mmHg-1, a 5-fold increase. A hyperbolic curve relating net barrier conductance to joint pressure was predicted from the hypothesis that interstitial conductance increases as a monotonic function of intra-articular pressure above yield pressure (Appendix). The data were in reasonable agreement with the theoretical hyperbola. Interstitial conductivity (3 X 10(-7)-7 X 10(-7) cm4 s-1 N-1 below yield pressure) and mean endothelial conductance (1.1 X 10(-4)-1.4 X 10(-4) cm3 s-1 N-1) were evaluated and compared with values in other tissues. Synovial endothelium contains on average 0.25 fenestrae micron-1 circumference. The conductance of a single fenestra was calculated to be 2.3 X 10(-13) cm5 s-1 N-1. Interstitial resistance accounted for roughly half the total resistance below yield point: therefore dQS/dPC should not be equated with 'capillary filtration capacity' in tissues with dense or fenestrated capillary beds. Large inconsistencies between interstitial conductivity and glycosaminoglycan concentration are noted, and mechanistic explanations of increases in conductivity with joint pressure are offered.

Ultrastructural study of long spacing collagen fibres and basal lamina in malignant schwannoma

It was found by electron microscopy that extracellular darkly stained materials (DSM) observed abundantly in a case of malignant schwannoma were closely related to both basal lamina and fibrous long spacing collagen (FLS). The FLS were characterized by the cross bands with a 95 nm periodicity, and longitudinally aligned filaments, 9 nm in diameter, while DSM consisted of amorphous material, and 9 nm filaments. The filaments in DSM and FLS were similar in diameter and morphology to reticular fibres in basal laminae. The DSM were continuous with both dark bands of FLS and basal laminae. These results indicate that basal laminae may be the common origin of DSM and FLS. Ultrastructural features of longitudinal, transverse and oblique sections were described.

Repair of the mouse synovial membrane after chemical synovectomy with osmium tetroxide

Repair of the synovium of the mouse knee joint following intra-articular injection with osmium tetroxide has been studied by light and electron microscopy. Within a first few days after osmium tetroxide injection complete necrosis of the synovial intima and inflammatory response in the subintimal connective tissue occurred. The resurfacing of the denuded synovium was performed by proliferation of immature synovioblasts which appeared to be derived from mesenchymal cells in the transition zone. The synovial intima completely restored the original structure, while repair of the subintimal tissue was accomplished by a scarring.

Ultrastructure of the mouse leptomeninx

An electron microscopic study was made of the mouse leptomeninx with special attention to the ultrastructure of the subarachnoid space. The arachnoid membrane was divided into outer and inner layers. The outer layer was composed of elongated cells in contact with one another with numerous tight junctions. The cells in the inner layer had intricate cytoprocesses , some of which embraced the connective tissue matrix containing collagen fibers. Beneath the arachnoid membrane, there were a loose meshwork of arachnoid cells and a single layer of pial cells. No arachnoid trabeculae were found. The intercellular space of the leptomeninx except in the outer layer of the arachnoid membrane was filled with Ruthenium Red-positive flocculent material and particles, in which various amounts of the collagen fibers and microfibrils were embedded. Elastic fibers were not identified. The subarachnoid space, which is believed to be a specialized channel exclusively containing the cerebrospinal fluid, was not recognized. These observations indicate that the cerebrospinal fluid circulates through the broad intercellular space, which contains extracellular matrix, of the leptomeninx .

Biological activity of lymphocytotoxic antibodies in Graves' disease and Hashimoto's thyroiditis

Sera of 48 patients with Graves' disease (GD) and 23 with Hashimoto's thyroiditis (HT) were tested for lymphocytotoxic (LCT), granulocytotoxic (GCT) and monocytotoxic (MCT) activity. In GD, 12 patients (25%) had cold-reacting LCT and 13 patients (27%) had warm-reacting LCT. LCT were cytotoxic to both B and T cells but the majority of sera with cold-reacting LCT and eluates from lymphocytes were more cytotoxic to B lymphocytes. Warm-reacting LCT were directed exclusively against B cells. LCT did not correlate with peripheral lymphocyte counts, antithyroglobulin or antimicrosomal antibodies, sex, age, pregnancies, thyroid status or medication. However the mean duration of the disease was 15 months in LCT positive group and 55 months in LCT negative group (p less than 0.01). Weak GCT were found in 8 of 35 sera (23%). Six of 33 sera (18%) contained cold-reacting MCT and 9 (27%) had warm-reacting MCT. Some cytotoxins were directed against several types of cells as evidenced by cytotoxicity of eluates from lymphocytes against PMN and/or monocytes. Of 23 patients with HT, 11 (48%) had cold-reacting LCT. None had warm-reacting LCT. Sera and eluates from lymphocytes showed predominant cytotoxicity toward B cells. No correlation to the presence of antibodies, sex, age, pregnancies, thyroid status or medication was detected. Four of 23 sera had weak cold-reacting GCT, 5 had cold-reacting MCT which killed on average 31% of monocytes and 4 had weak warm-reacting MCT. Twelve of 22 sera from GD and HT had cytotoxic activity against thyroid cells (TCT). TCT correlated with LCT at p less than 0.05.(ABSTRACT TRUNCATED AT 250 WORDS)