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

The pathogenesis of oligoarticular/polyarticular vs systemic juvenile idiopathic arthritis

Juvenile idiopathic arthritis (JIA) has had a long and difficult problem with classification. It is clearly a heterogeneous and multi-factorial autoimmune disease but all too often the distinctions among subtypes were unclear. In fact, there is now increasing evidence of a distinct pathogenesis of oligo/polyarticular JIA compared to systemic JIA. Oligo/polyarticular JIA is an antigen-driven lymphocyte-mediated autoimmune disease with abnormality in the adaptive immune system. Cartilage-derived auto-antigens activate autoreactive T cells including Th1 and Th17 cells with production of pro-inflammatory cytokines IFN-γ and IL-17. On the other hand, the inhibition of regulatory T (Treg) cells including natural Foxp3(+) Treg and self-heat shock protein-induced Treg cells with decreased anti-inflammatory cytokine IL-10 results in the loss of immune tolerance. Imbalance between autoreactive Th1/Th17 and Treg cells leads to the failure of T cell tolerance to self-antigens, which contributes to the synovial inflammation of oligo/polyarticular JIA. By contrast, systemic JIA is an autoinflammatory disease with abnormality in the innate immune system. A loss of control of the alternative secretory pathway leading to aberrant activation of phagocytes including monocytes, macrophages and neutrophils seems to be involved in the release of pro-inflammatory cytokines IL-1, IL-6, IL-18 and pro-inflammatory S100-proteins, which contribute to the multisystem inflammation of systemic JIA. Markedly distinct pathogenesis of oligo/polyarticular JIA and systemic JIA implies that they might need different treatment strategies.

Synovial fibroblasts self-direct multicellular lining architecture and synthetic function in three-dimensional organ culture

OBJECTIVE

To define the intrinsic capacity of fibroblast-like synoviocytes (FLS) to establish a 3-dimensional (3-D) complex synovial lining architecture characterized by the multicellular organization of the compacted synovial lining and the elaboration of synovial fluid constituents.

METHODS

FLS were cultured in spherical extracellular matrix (ECM) micromasses for 3 weeks. The FLS micromass architecture was assessed histologically and compared with that of dermal fibroblast controls. Lubricin synthesis was measured via immunodetection. Basement membrane matrix and reticular fiber stains were performed to examine ECM organization. Primary human and mouse monocytes were prepared and cocultured with FLS in micromass to investigate cocompaction in the lining architecture. Cytokine stimuli were applied to determine the capacity for inflammatory architecture rearrangement.

RESULTS

FLS, but not dermal fibroblasts, spontaneously formed a compacted lining architecture over 3 weeks in the 3-D ECM micromass organ cultures. These lining cells produced lubricin. FLS rearranged their surrounding ECM into a complex architecture resembling the synovial lining and supported the survival and cocompaction of monocyte/macrophages in the neo-lining structure. Furthermore, when stimulated by cytokines, FLS lining structures displayed features of the hyperplastic rheumatoid arthritis synovial lining.

CONCLUSION

This 3-D micromass organ culture method demonstrates that many of the phenotypic characteristics of the normal and the hyperplastic synovial lining in vivo are intrinsic functions of FLS. Moreover, FLS promote survival and cocompaction of primary monocytes in a manner remarkably similar to that of synovial lining macrophages. These findings provide new insight into inherent functions of the FLS lineage and establish a powerful in vitro method for further investigation of this lineage.

A Role for Hyaluronan in the Preservation of Interstitial Structure

Hydraulic resistance of interstitium is of major importance in body fluid distribution. In the synovial lining it is vital for the retention of intra-articular fluid, and is attributed chiefly to the network of interstitial biopolymers occupying intercellular gaps in the tissue. Selective removal of synovial hyaluronan (HA) by protease-free hyaluronate lyase results in an almost 10x increase in synovial hydraulic permeability from 0.48 +/- 0.24 microL min(-1) cm H2O (control) to 4.56 +/- 0.40 microL min(-1) cm H2O (mean +/- SD, n = 6 rabbits, p < .001, t test) leading to the hypothesis that hyaluronan plays a major role in the organization of interstitial matrix structure. To test whether removal of hyaluronan causes significant changes in synovial ultrastructure, morphometry of hyaluronidase-treated synovium was carried out. Following hyaluronidase, the thickness of the synovial lining was reduced from 13.0 +/- 1.6 microm (control) to 10.6 +/- 1.6 microm (mean +/- SD throughout, n = 50 measurements per rabbit, 6 rabbits. p < .001, t test). This was accompanied by a significant reduction of synovial interstitial volume fraction from 76.2 +/- 20.6% (control) to 67.04 +/- 24.94% (p < .001, t test), and an increase in collagen bundle volume as a fraction of interstitial volume from 40.75 +/- 4.97% (control) tissue to 48.77 +/- 11.72% (p < .0001, t test). The findings indicate that the removal of hyaluronan chains leads to morphological disruption. Thus, hyaluronan chains play a major role in the organization of synovial structure. The observed morphological changes are insufficiently large to explain fully the great rise in hydraulic permeability observed on HA removal. The latter is likely to be due to disruption of tertiary architecture at the molecular organization level.

Novel self-epitopes derived from aggrecan, fibrillin, and matrix metalloproteinase-3 drive distinct autoreactive T-cell responses in juvenile idiopathic arthritis and in health

Juvenile idiopathic arthritis (JIA) is a heterogeneous autoimmune disease characterized by chronic joint inflammation. Knowing which antigens drive the autoreactive T-cell response in JIA is crucial for the understanding of disease pathogenesis and additionally may provide targets for antigen-specific immune therapy. In this study, we tested 9 self-peptides derived from joint-related autoantigens for T-cell recognition (T-cell proliferative responses and cytokine production) in 36 JIA patients and 15 healthy controls. Positive T-cell proliferative responses (stimulation index ≥2) to one or more peptides were detected in peripheral blood mononuclear cells (PBMC) of 69% of JIA patients irrespective of major histocompatibility complex (MHC) genotype. The peptides derived from aggrecan, fibrillin, and matrix metalloproteinase (MMP)-3 yielded the highest frequency of T-cell proliferative responses in JIA patients. In both the oligoarticular and polyarticular subtypes of JIA, the aggrecan peptide induced T-cell proliferative responses that were inversely related with disease duration. The fibrillin peptide, to our knowledge, is the first identified autoantigen that is primarily recognized in polyarticular JIA patients. Finally, the epitope derived from MMP-3 elicited immune responses in both subtypes of JIA and in healthy controls. Cytokine production in short-term peptide-specific T-cell lines revealed production of interferon-γ (aggrecan/MMP-3) and interleukin (IL)-17 (aggrecan) and inhibition of IL-10 production (aggrecan). Here, we have identified a triplet of self-epitopes, each with distinct patterns of T-cell recognition in JIA patients. Additional experiments need to be performed to explore their qualities and role in disease pathogenesis in further detail.

Evidence for a role of hyaluronan in the spacing of fibrils within collagen bundles in rabbit synovium

Synovial hydraulic resistance is vital for the retention of intra-articular fluid, and originates within the matrix of biopolymers in the intercellular gaps. Specific digestion of hyaluronan resulted in a increase in synovial hydraulic permeability from 0.478+/-0.24 microl min(-1) cm H(2)O(-1) in control tissue to 4.561+/-0.40 microl min(-1) cm H(2)O(-1) (mean+/-S.D., n=6 rabbits, P<0.001 t test). To investigate whether hyaluronidase also altered the interstitial ultrastructure, morphometry of hyaluronidase treated synovium was carried out. The most striking novel finding was that hyaluronidase treatment reduced extrafibrillar volume fraction within the synovial collagen bundles from 50.5+/-11.1% to 36.8+/-15.5% (mean+/-S.D., n=6 rabbits, P<0.001, two-way anova). This was accompanied by a reduction in interfibrillar centre to centre spacing from 101+/-11 (control) to 84+/-6 nm (mean+/-S.D.; n=6 rabbits, P<0.001) in enzyme-treated bundles. Individual fibrils showed a small but highly significant reduction in cross-sectional diameter from 76.9+/-6.3 to 72.5+/-6.3 nm (mean+/-S.E.; P<0.001) after hyaluronidase treatment. The findings indicate that hyaluronan chains have a major organisational role within the collagen bundle itself. The trans-synovial pathway comprises bundles and substantial areas of intervening, bundle-free matrix, and it is possible that bundle collapse contributes to a rise in overall permeability by increasing the inter-bundle space.

Fibrillin-rich microfibrils of the extracellular matrix: ultrastructure and assembly

Fibrillin-rich microfibrils are a unique class of extensible connective tissue macromolecules. Their critical contribution to the establishment and maintenance of diverse extracellular matrices was underlined by the linkage of their principal structural component fibrillin to Marfan syndrome, a heritable connective tissue disorder with pleiotropic manifestations. Microscopy and preparative techniques have contributed substantially to the understanding of microfibril structure and function. The supramolecular organisation of microfibrillar assemblies in tissues has been examined by tissue sectioning and X-ray diffraction methods. Published findings are discussed and new information reported on the organisation of microfibrils in the ciliary zonular fibrils by environmental scanning electron microscopy. This review summarises microscopy and X-ray diffraction studies that are informing current understanding of the ultrastructure of fibrillin-rich microfibrils.

In the mammalian eye type VI collagen tetramers form three morphologically different aggregates

The organization of the aggregates occurring in the stroma: (1) of the murine and human cornea after incubation in an ATP acidic solution; (2) of surgically excised epiretinal membranes (ERM); and (3) of the trabecular meshwork of monkey eyes was investigated morphologically and immunocytochemically on thin section electron microscopy. Morphology. The aggregates in the cornea appeared as cross-banded fibrils. The bands were uniformly electron dense (single banded form); they were separated from each other by interbands consisting of a bundle of filaments emerging in cross section as small areas of randomly assembled dot-like structures. In the ERM, most of the aggregates stood out as heteromorphic cross-banded bodies showing dense bands with electron denser borders (double banded form) and interbands composed of longitudinally oriented, parallel sheets or laminae of amorphous material enclosing thin, similarly oriented filaments. These extended, thinner and double in number (since interlacing with similar components of the opposite sheet), into the pale central zone of the dense band. The aggregates of the trabecular meshwork were heteromorphic, had uniformly dense bands (single banded form as in the cornea), but their interbands displayed longitudinal sheets (as the ERM aggregates). Immunocytochemistry revealed type VI collagen in the three eye aggregates with gold particles preferentially localized at the interbands. The specificity of the antibodies used was tested by Western blot analysis of type VI collagen samples extracted from human placenta and on homogenates of human cornea. In conclusion, the results indicate that the tetramers of type VI collagen may aggregate differently into structures with distinct supramolecular arrangements. These are illustrated in schematic drawings.

Fibroblast biology. Development and differentiation of synovial fibroblasts in arthritis

Synovial fibroblasts occur as two phenotypes--intimal and subintimal. The specialised intimal phenotype includes expression of uridine diphosphoglucose dehydrogenase (UDPGD), vascular cell adhesion molecule-1 (VCAM-1) and complement decay-accelerating factor (DAF). These gene products contribute to specialised functions relating to tissue movement and leucocyte traffic.

Fibrillin-rich microfibrils are reduced in photoaged skin. Distribution at the dermal-epidermal junction

Chronic sun exposure results in photoaged skin with deep coarse wrinkles and loss of elasticity. We have examined the distribution and abundance of fibrillin-rich microfibrils, key structural components of the elastic fiber network, in photoaged and photoprotected skin. Punch biopsies taken from photoaged forearm and from photoprotected hip and upper inner arm of 16 subjects with a clinical range of photoaging were examined for fibrillin-1 and fibrillin-2 expression and microfibril distribution. In situ hybridization revealed decreased fibrillin-1 mRNA but unchanged fibrillin-2 mRNA levels in severely photoaged forearm biopsies relative to photoprotected dermal sites. An immunohistochemical approach demonstrated that microfibrils at the dermal-epidermal junction were significantly reduced in moderate to severely photoaged forearm skin. Confocal microscopy revealed that the papillary dermal microfibrillar network was truncated and depleted in photoaged skin. These studies highlight that the fibrillin-rich microfibrillar network associated with the upper dermis undergoes extensive remodeling following solar irradiation. These changes may contribute to the clinical features of photoaging, such as wrinkle formation and loss of elasticity.

The proteoglycans and glycosaminoglycan chains of rabbit synovium

The synovial lining of joint capsules is important because it controls the flow of fluid into and out of the joint cavity. Physiological studies have shown that the glycosaminoglycans, particularly hyaluronan, have an important role in the control of fluid flow. The distribution of the glycosaminoglycans and proteoglycans in the synovium and subsynovium of rabbits (approximately 12 weeks old) was, therefore, determined immunohistochemically. Hyaluronan, chondroitin-4- and chondroitin-6-sulphates and keratan sulphate are present in the synovium and subsynovium; chondroitin-4-sulphate is at higher concentrations than chondroitin-6-sulphate. The core proteins of the chondroitin sulphate proteoglycans, biglycan and decorin, and of the keratan sulphate proteoglycan, fibromodulin, are also present. To date, fibromodulin has not been located in other synovial linings, and its presence corroborates that of keratan sulphate.

Fibrillin microfibrils are reduced in skin exhibiting striae distensae

Striae distensae (striae: stretch marks) are a common disfiguring condition associated with continuous and progressive stretching of the skin--as occurs during pregnancy. The pathogenesis of striae is unknown but probably relates to changes in those structures that provide skin with its tensile strength and elasticity. Such structures are components of the extracellular matrix, including fibrillin, elastin and collagens. Using a variety of histological techniques, we assessed the distribution of these extracellular matrix components in skin affected by striae. Pregnant women were assessed for the presence of striae, and punch biopsies were obtained from lesional striae and adjacent normal skin. Biopsies were processed for electron microscopy, light microscopy and immunohistochemistry. For histological examination, 7 microns frozen sections were stained so as to identify the elastic fibre network and glycosaminoglycans. Biopsies were also examined with a panel of polyclonal antibodies against collagens I and III, and fibrillin and elastin. Ultrastructural analysis revealed alterations in the appearance of skin affected by striae compared with that of normal skin in that the dermal matrix of striae was looser and more floccular. Light microscopy revealed an increase in glycosaminoglycan content in striae. Furthermore, the number of vertical fibrillin fibres subjacent to the dermal-epidermal junction (DEJ) and elastin fibres in the papillary dermis was significantly reduced in striae compared with normal skin. The orientation of elastin and fibrillin fibres in the deep dermis showed realignment in that the fibres ran parallel to the DEJ. However, no significant alterations were observed in any other extracellular matrix components. This study identifies a reorganization and diminution of the elastic fibre network of skin affected by striae. Continuous strain on the dermal extracellular matrix, as occurs during pregnancy, may remodel the elastic fibre network in susceptible individuals and manifest clinically as striae distensae.

Differential distribution of Fc gamma RIIIa in normal human tissues and co-localization with DAF and fibrillin-1: implications for immunological microenvironments

Fc gamma RIIIa is a cytokine-inducible IgG Fc receptor implicated in the activation of macrophages by immune complexes. Differential expression of Fc gamma RIIIa by macrophages in different tissues may therefore modulate local immune responsiveness. Fc gamma RIIIa expression in normal human tissues was assessed semiquantitatively using microdensitometry. Synovial intimal, serosal, alveolar, salivary gland and placental macrophages, Kupffer cells, and macrophages in mechanically stressed dermis expressed high levels of Fc gamma RIIIa. Less consistent expression was seen in skeletal muscle and lymphoid organs. No significant expression was observed in brain, thyroid, spine, intestine, myocardium, prostate, uterus, flexor forearm dermis, uterus, or kidney. Staining for Fc gamma RIII was also observed on extracellular matrix, and co-localized with both complement decay-accelerating factor and fibrillin-1. It is proposed that differential levels of both cellular and extracellular Fc gamma RIIIa, by modulating the response to immune complexes, may contribute to relative tissue susceptibility to infection and autoimmune disease.

Characterization of collagens and proteoglycans at the insertion of the human Achilles tendon

This study provides a unique correlation between a molecular biological and biochemical analysis of the extracellular matrix (ECM) macromolecules in one half of 28 human Achilles tendons with an immunohistochemical study of the other. Both the insertion site and the mid-tendon were studied. The insertion (enthesis) is characterized by three distinctive fibrocartilages, two in the tendon (enthesial and sesamoid) and one on the heel bone (periosteal). Thus, its structure contrasts markedly with the fibrous character of the mid-tendon. RT-PCR analyses were performed on RNA extracted from mid-tendon and from the tendon fibrocartilages to investigate transcription of collagens and proteoglycans. Western blotting was also used to identify and characterize these macromolecules, and immunohistochemistry to localize their distribution. The results demonstrate striking differences in the ECM between the mid-tendon and its insertion. Types I, III, V and VI collagens, decorin, biglycan, fibromodulin and lumican were found in both the mid-tendon and the fibrocartilages, although their precise distribution often differed with site. mRNA for type II collagen was constantly present in the fibrocartilages, but it was only found in the mid-tendon of one specimen. The patterns of distribution for versican and aggrecan mRNA were complimentary - versican mRNA was present in the mid-tendon and absent from the fibrocartilages, while aggrecan mRNA was present in the fibrocartilages and absent from the mid-tendon. The range and distribution of ECM molecules detected in the Achilles tendon reflect the differing forces acting on it - the mid-tendon largely transmits tension and is characterized by molecules typical of fibrous tissues, but the fibrocartilages must also resist compression and thus contain, in addition, molecules typical of cartilage.

Advances in the microscopy of osteoarthritis

This review describes recent contributions made by microscopy to the understanding of osteoarthritis, a clinical syndrome the pathological features of which are well defined by classical white light microscopy. The fluorescence and reflected light, conventional and scanning optical microscopy of excised osteoarthritic tissue preparations, from human and animal sources, has enabled the identification of cell proteins such as S100, of matrix components such as the proteoglycans and collagens, and of adhesion molecules including fibronectin, the integrins and tenascin. Comparable microscopic studies have been made of cell and tissue culture preparations of osteoarthritic cartilage and synovium. Scanning optical microscopy also allows the rapid measurement, in hydrated osteoarthritic tissues, of cell density, cell size, surface roughness and other parameters. The importance of water in sustaining the physical attributes of cartilage is accepted and new forms of electron microscopy can play important parts in the study of unfixed osteoarthritic cartilage. These methods include the low temperature scanning electron microscopy and electron probe x-ray microanalysis of hydrated bulk material and the high resolution transmission electron microscopy of low temperature replicas of cartilage surfaces. Understanding of osteoarthritis has been facilitated by these advances and will continue to be enhanced as new techniques of microscopy evolve.

An immunohistochemical study of collagen types III, VI and IX in rabbit craniomandibular joint tissues following surgical induction of anterior disk displacement

The purpose of this study was to determine the effect of surgical induction of anterior disk displacement (ADD) on type-III, VI and IX collagens of the rabbit craniomandibular joint (CMJ) tissues using an immunohistochemical technique. The right joint was exposed surgically, all discal attachments were severed except for the posterior discal attachment (bilaminar zone). The disk was then repositioned anteriorly and sutured to the zygomatic arch. The left joint served as a sham-operated control. Ten additional joints were used as non-operated controls. Deeply anesthetized rabbits were perfused with 2% buffered formalin 2 weeks (10 rabbits) or 6 weeks (10 rabbits) following surgery. The articular disk, bilaminar zone, mandibular condyle and articular eminence were excised. The last two were decalcified in EDTA. All tissues were then sectioned at 10 microns in a cryostat. Sections were incubated with monoclonal antibodies directed against type-III, VI or IX collagens. Following incubation in the appropriate FITC-labelled secondary antibodies, all sections were studied under the fluorescence microscope. The results showed a reduction in immunostaining for type-VI and IX collagens in the condylar cartilage, disk and articular eminence at 2 weeks, followed by an increase in their immunostaining at 6 weeks and the appearance of a de novo type-III collagen in the condylar cartilage and the articular eminence. It is concluded that surgical induction of ADD in the rabbit CMJ leads to alterations in its type-III, VI and IX collagens.

Analyses of truncated fibrillin caused by a 366 bp deletion in the FBN1 gene resulting in Marfan syndrome

We studied fibrillin synthesis in cultured fibroblasts from 11 members of a three-generation family with Marfan syndrome, caused by a large in-frame deletion in FBN1 (the fibrillin gene) leading to a loss of 366 bases in the corresponding fibrillin mRNA. Metabolic labelling with [35S]Met/Cys and SDS/PAGE allowed unequivocal identification of normal and truncated fibrillin in all cell strains harbouring the deletion. In culture medium, fibrillin and its truncated counterpart were predominant, whereas their respective larger precursors were found only in traces. This proportion, however, was markedly shifted towards the normal and truncated precursors by EGTA and reversed by the addition of calcium, which confirmed the existence of profibrillin and its probably calcium-dependent conversion into fibrillin. Tunicamycin caused increased electrophoretic mobility of normal and truncated molecules without changing their apparent size differences. Intracellularly, only profibrillin was found; in the mutant cells truncated and normal profibrillin molecules were present in similar amounts and both populations were secreted and deposited simultaneously into the extracellular matrix; there, however, truncated profibrillin only became easily detectable after treatment of cells with dextran sulphate, which increased the amount of extractable profibrillin. Immunofluorescence microscopy in patients' cultures identified fibrillin-containing microfibrils which appeared to be moderately reduced both in amount and diameter. Ultrastructural analysis by rotary-shadowing and immunogold electron microscopy demonstrated the presence of numerous beaded domains reacting with fibrillin antibodies, but no intact fibrillin microfibrils in patient's cell-layer extracts, in contrast with the extensive microfibrils elaborated by control cultures. Our findings suggest, that in the patients' cell cultures all microfibrils contained the truncated fibrillin molecules.

An ultrastructural study of extracellular fibrillar components of developing mouse mandibular condyle with special reference to type VI collagen

The localization of type VI collagen was examined from birth to 8 weeks of age. Immunohistochemical staining with anti-type VI collagen antibody was strongly positive in the hypertrophic zone and moderately positive in the fibrous zone and the outer periphery of the proliferative zone, but negative in the inner area of the proliferative zone and mature zone. After ATP treatment, type VI collagen periodic fibrils with about 80-nm intervals were frequently observed but only in the fibrous zone. They occurred mainly in the superficial area of this zone, where striated collagen fibrils were sparse, while a few were noted in the inner area, where bundles of collagen fibrils were abundant. From these distributional differences of both components, a subzonation of the fibrous zone into superficial and inner area is suggested. Moreover, with ATP treatment there were fewer type VI collagen periodic fibrils formed with increasing age (8 weeks). Testicular hyaluronidase digestion before ATP treatment facilitated the formation of periodic fibrils, in all the ages examined, in the intercellular space and around the fibroblastic cells. The interaction of type VI collagen with other components such as collagen fibrils, glycosaminoglycans or proteoglycans may play a part in maintaining the structural integrity of extracellular matrix in the mouse mandibular condyle.

Abnormal fibrillin assembly by dermal fibroblasts from two patients with Marfan syndrome

The microfibrillar glycoprotein fibrillin is linked to the Marfan syndrome, an autosomal dominant connective tissue disorder. In this study, fibrillin synthesis, deposition and assembly has been investigated in Marfan dermal fibroblast lines from two unrelated patients for whom distinct mutations in the fibrillin gene FBN1 have been identified. In patient NB, a point mutation has occurred which causes an amino acid substitution and the other patient (GK) has a deletion in one allele. The two cell lines were broadly comparable with respect to de novo fibrillin synthesis and its distribution between medium and cell layer compartments. Electrophoresis of fibrillin immunoprecipitates confirmed the presence of fibrillin in medium and cell layers. GK cells secreted an additional higher relative molecular mass fibrillin-immunoreactive component. The time-course of fibrillin secretion was similar for the two lines, but differences in fibrillin aggregation were apparent. Rotary shadowing electron microscopy of extracted cell layers demonstrated the presence of abundant and extensive microfibrils in NB cell layers. These were abnormal in their gross morphology in comparison to microfibrils isolated from control cultures. No periodic microfibrillar structures were isolated from GK cell layers. These studies underline the need to classify fibrillin defects in terms of biochemical and ultrastructural criteria. Examination of the effects of individual mutations on microfibril organization will be particularly informative in elucidating the relationship between microfibril dysfunction and the complex clinical manifestations of Marfan patients.

Fibrillin secretion and microfibril assembly by Marfan dermal fibroblasts

The Marfan syndrome has been linked to the FBN1 gene encoding the microfibrillar glycoprotein fibrillin. To date, there have been no descriptions of microfibrillar abnormalities characteristic of this connective tissue disorder, although biochemical analyses have highlighted apparent abnormalities in fibrillin synthesis, secretion and processing. We have conducted a biochemical and ultrastructural investigation of fibrillin expression and assembly by a panel of dermal fibroblast lines from patients with Marfan syndrome and related diseases. The study has highlighted marked differences between cells in terms of secretion and aggregation of newly-synthesised fibrillin. In addition, electron microscopic visualization of fibrillin assemblies has clearly demonstrated for the first time the plethora of microfibrillar abnormalities that underlie this heterogeneous disorder. These data emphasize the molecular complexity that is a feature of the diverse clinical phenotypes exhibited by Marfan patients.