Extracellular matrix and epithelial differentiation of Wilms' tumor

Different histologic types of 82 Wilms' tumors were graded on the basis of the histologic pattern. Representative tumors of each group were analyzed by the immunoperoxidase method for evaluation of the histogenesis of Wilms' tumor and the value of antibodies against extracellular matrix (ECM) components (collagens I and III, laminin, fibronectin) in differential diagnosis of different types of Wilms' tumors. The tubules of classic Wilms' tumor expressed laminin, which could be seen also in and around some blastemal cells. Blastema and tubules were negative for interstitial collagens, but Type I and III collagen were prominent in the fibrovascular stroma. The monomorphous tubular, psammomatous and rosetting tumors expressed laminin, but no interstitial collagens. In sarcomas, only the blastemal variant of spindle-cell sarcomas was negative for interstitial collagens, which were abundantly seen in all other sarcomas. While spindle-cell sarcomas were devoid of laminin, the highly malignant rhabdoid and clear-cell sarcomas expressed laminin in a characteristic dotted fashion. Staining for fibronectin gave varying results and had therefore only a limited value in distinguishing different types of Wilms' tumors. However, the antibodies against interstitial collagens and against the basement membrane glycoprotein laminin turned out to be a useful adjunct in differential diagnosis and classification, especially of sarcomatoid Wilms' tumors. The basement membrane of normal nephrons is similar to that in tubules of triphasic Wilms' tumor, but the ECM of blastemas is different. This transformed phenotype might represent a maturation arrest of the blastemal cell when compared with the expression of proteins during normal nephrogenesis.     

A histologic study of the extracellular matrix during the development of glomerulosclerosis in murine chronic graft-versus-host disease.

The development of glomerulosclerosis was studied in murine chronic graft-versus-host disease (GvHD), which is a model for human systemic lupus erythematosus. The authors investigated the distribution patterns of six components of the extracellular matrix (ECM), i.e., laminin, fibronectin, collagen types I, III, IV, and VI during the course of the disease. All of these ECM components except collagen type I were found in the glomeruli of normal mice, where all of them were intrinsic constituents of the mesangium. Laminin, fibronectin, and collagen type IV were also found in the glomerular capillary walls. Starting 6 weeks after the induction of GvHD and continuing at week 8, the onset of an expansion of the mesangial matrix was observed. At the same time, the amounts of laminin, fibronectin, and collagen types IV and VI increased. Ten weeks after the onset of the disease, glomerulosclerosis developed. Traces of the interstitial collagen type I were found in sclerotic glomeruli. The levels of four ECM components, i.e., collagens III, IV, VI, and laminin were markedly decreased in the sclerotic glomeruli as compared with week 8. In contrast, the amount of fibronectin in the sclerotic glomeruli increased dramatically. Immunoelectron microscopic examination showed fibronectin in the sclerotic lesions, in contrast to laminin, collagen type I, and collagen type IV. It is concluded that the sclerotic lesions in murine chronic GvHD contain fibronectin. The small amounts of the ECM components laminin, as well as collagens III, IV, and VI in the sclerotic glomeruli in GvHD, might represent remnants of mesangial material and collapsed capillary walls. These components are probably replaced by increased production and/or accumulation of collagen type I and fibronectin.     

Immunolocalization of extracellular matrix proteins and collagen synthesis in first-trimester human decidua

The extracellular matrix (ECM) of first-trimester human decidua was examined with indirect immunofluorescence using affinity-purified antibodies to human collagen types I, III, IV, V, laminin, and fibronectin. In addition, the validity of the classification "mesenchymal-epithelioid" for differentiated decidual cells was addressed using antibodies to the intermediate filament proteins, vimentin, a mesenchymal marker, and keratin, an epithelial marker. Biosynthesis of extracellular matrix components was examined by radiolabeling of decidual explants in culture with 3H-proline, followed by immunoprecipitations of synthesized proteins with collagen type-specific antibodies. Immunofluorescence showed decidual cells are embedded in an extensive network of collagen types I and III, and intracytoplasmic staining suggested synthesis of these collagens by the decidual cells. Collagen type IV and laminin localized in the external lamina which surrounds the differentiated decidual cell, and some fluorescence was evident in the peripheral cytoplasm. Immunoreactive collagen type V was observed in close association with the external lamina and in the peridecidual matrix. Fibronectin localized throughout the decidual ECM and in fibrillar and punctuate patterns in the decidual cell cytoplasm. Differentiated decidual cells retained a "mesenchymal" intermediate filament cytoskeleton containing an abundance of vimentin filaments, but very few, if any, keratin filaments. Collagen types I, III, V, and to a lesser extent, IV, were immunoprecipitated from the medium of decidual explants after 24 hours of culture, demonstrating in vitro synthesis and secretion of these collagens by first trimester human decidua.     

Formation of extracellular matrix by cultured rat mesangial cells.

Formation of extracellular matrix (ECM) by mesangial cells (MCs) contributes to progressive glomerulosclerosis. The authors investigated the production and distribution of ECM constituents by cultured rat MCs, using immunocytochemistry and immunoelectron microscopy. Staining for all ECM constituents increased after serum feeding. Localization was strictly intracellular until confluency, when extracellular deposition of collagen IV and laminin appeared, followed by fibronectin and collagen III. In parallel, the intracellular staining for these proteins diminished markedly. Neither extracellular deposition nor intracellular loss was observed for collagen I and thrombospondin. On surfaces coated with collagen IV or laminin, extracellular deposition of ECM constituents clearly preceded confluency. These results indicate that synthesis of ECM constituents parallels MC growth, and that extracellular deposition of ECM occurs at cell-cell contact. Collagen IV or laminin secreted by MCs in the substratum accelerates production and facilitates secretion of other ECM constituents in an autocrine fashion.     

The extracellular matrix in large-cell lymphomas: a histopathologic, immunohistochemical, and ultrastructural study

We studied the histopathologic, immunohistochemical, and ultrastructural features of the extracellular matrix (ECM) in 20 immunologically defined large-cell lymphomas, including immunoblastic sarcoma of B cells (three patients), peripheral T cell lymphoma (five patients), large non-cleaved follicular center cell (FCC) lymphoma (nine patients), and non-marking large-cell lymphoma (three patients). Immunohistochemical studies were performed with antibodies to laminin, fibronectin, and collagen types I, III, IV, and V. The immunologically defined subgroups demonstrated characteristic differences in ECM in light microscopic appearance, composition, and ultrastructural features. Immunoblastic sarcomas of B cells showed delicate intercellular bands that were apparent only at high power but were distinct in exhibiting focal staining for basement membrane elements (laminin and type IV collagen) in addition to type I collagen and fibronectin. Electron microscopically, no basal lamina were apparent, although the collagen fibers were embedded in a dense matrix not seen in the other lymphomas. All peripheral T cell lymphomas exhibited a packeting pattern of intercellular bands and were distinguished by the frequent presence of intense pericellular staining for type V collagen as well as by focal pericellular staining for types I and III collagen. The latter finding corresponded to extensive areas of direct contact between tumor cells and the ECM by electron microscopy. The large non-cleaved FCC lymphomas and the non-marking large-cell lymphomas demonstrated both diffuse and compartmentalizing arrangements of intercellular bands that frequently coexisted and stained predominantly for fibronectin and types I and III collagen. All groups demonstrated myofibroblasts and fibroblasts partially or completely separating the ECM from tumor cells, suggesting that most of the ECM is part of a reaction to these lymphomas. These studies show more variation in light microscopic appearance, composition, and ultrastructural relationships of the intercellular and pericellular ECM than was apparent in earlier studies of cleaved FCC lymphomas.     

The microvascular extracellular matrix. Developmental changes during angiogenesis in the aortic ring-plasma clot model.

The composition of the extracellular matrix of developing microvessels in plasma clot cultures of rat aorta was studied with light and electron immunohistochemical techniques using affinity-purified antibodies against fibronectin, laminin, and collagen Types I, III, IV, and V. The extracellular matrix of solid endothelial sprouts in young cultures consisted of a delicate fibrillary network of fibronectin and Type V collagen and of patchy amorphous deposits of laminin and Type IV collagen. Rare fibrils of collagen Types I and III were also observed. Fibronectin stained intensely and appeared to be the predominant component of the provisional subendothelial matrix during vascular sprouting. As the cultures aged, laminin and Type IV collagen accumulated in the subendothelial space, forming a continuous feltwork around the newly formed microvessels. Patent microvessels were also surrounded by discontinuous deposits of fibronectin and by increased amounts of collagen Types I, III, and V. Ultrastructural studies revealed positive immunostaining for fibronectin, laminin, and collagen Types IV and V in the endoplasmic reticulum and in putative secretory vesicles, indicating active synthesis and secretion of these molecules by the endothelial cells. These observations indicate that the microvascular extracellular matrix undergoes significant dynamic changes during capillary development. The different composition and structural organization of the extracellular matrix at various stages of angiogenesis may have important effects on endothelial behavior and capillary morphogenesis.     

Localization of collagen types I, III, IV and V, fibronectin and laminin in human arteries by the indirect immunofluorescence method

The distribution of types I, III, IV and V collagen and of the glycoproteins fibronectin and laminin in sections of human aortas, arteries and atherosclerotic plaques were studied using monospecific antibodies and indirect fluorescence microscopy. Types IV and V collagen and laminin were present in a narrow zone, representing the basement membrane, apposed to the endothelial layers of all these tissues. Types I and III collagen and fibronectin were located in the interstitial spaces of the intima and the media of blood vessels walls, whereas types IV and V collagen and laminin were found in the basement membranes underlying smooth muscle cells in these areas. Two types of atherosclerotic plaques were observed. Lipid-rich plaques contained less collagen and reduced amounts of the glycoproteins. Fibrous plaques consisted of regions deficient in types I and III collagen and collagen-rich regions with elevated levels of these two collagens as well as more fibronectin. The collagen-rich regions of fibrous plaques contained, however, little type IV and type V collagen and little of the glycoproteins laminin and fibronectin. This may be due to the reduced number of cells involved in the biosynthesis of these basement membrane proteins.     

Extracellular matrix proteins and integrin receptors in reactive and non-reactive lymph nodes.

The extracellular matrix (ECM) proteins collagen I, III and IV, laminin, fibronectin, vitronectin, thrombospondin, tenascin and their integrin receptors of the beta 1 and beta 3 subfamilies showed characteristic patterns of distribution in different compartments of non-reactive and reactive lymph nodes (human and monkey). This was particularly evident during development of germinal centres. Thus, ECM proteins (collagens, laminin, fibronectin and tenascin) were abundant in the interfollicular (T-cell rich) compartments of non-reactive as well as reactive lymph nodes. In primary follicles, collagen I, III and fibronectin were expressed but displaced by the expanding germinal centre during the formation of secondary follicles in reactive lymphoid tissues. The integrin subunits were mainly associated with endothelial cells and lymphoid cells in interfollicular areas, but were absent or only poorly expressed in primary as well as secondary follicles. Evidently the expression of ECM components and their integrin receptors is markedly down-regulated in the reactive, highly proliferative germinal centres.     

Radioimmunoassay for human type II collagen.

Human articular cartilage type II collagen (h coll.II) was purified and used to develop a radioimmunoassay. The sequential saturation procedure allowed a sensitivity of 3 ng/tube. The intra and between assay coefficients of variation were less than 10 and 20% respectively in the linear part of the curve. The assay was highly specific for native human articular type II collagen. There was no cross-reactivity with other constituents of cartilage: human proteoglycans, fibronectin, laminin and hyaluronic acid did not interfere with the assay. No cross-reactivity existed with bovine collagen types I, III, IV. However, native collagens from human placenta (I, III, IV, V, VI), rat and calf skin type I collagens and bovine type II collagen produced a weak cross-reaction only at high doses. Concerning the latter, inhibition curves were not parallel. Parallelism of inhibition curves were observed for dilution of type II collagen, produced by human chondrocytes in three-dimensional culture. All of these characteristics indicate that radioimmunoassy of type II collagen is a very sensitive and specific method available for the study and quantification of type II collagen in in vitro experimental conditions.     

Immunohistochemical localization of extracellular matrix components in human diabetic glomerular lesions.

The immunohistochemical localization of the extracellular matrix was examined in 31 cases with different degrees of human diabetic nephropathy using antisera to human collagen types I, III, IV, V, fibronectin, laminin, and basement-membrane-associated heparan sulfate proteoglycan (HSPG). In normal glomeruli, HSPG was predominantly localized in the glomerular basement membrane and in the mesangium, and to minor extent in the basement membranes of tubules and Bowman's capsule. Collagen IV and laminin were distributed in glomerular basement membrane and mesangium in minor amounts. Interstitial collagens usually do not occur within glomeruli except for collagen V which has a light microscopic glomerular distribution similar to collagen IV. In diabetic diffuse glomerulosclerosis, the enlarged mesangial matrix showed an increased staining reaction for collagen IV, V, laminin, and fibronectin whereas the staining pattern of HSPG was markedly reduced. Early, small nodular lesions in diabetic glomeruli were similarly positive for most of the basement membrane components, whereas HSPG remained absent. With an increase in the diameter of the noduli, however, the staining reaction for all basement membrane components diminished, whereas interstitial collagens V and III, but not collagen I, were present in these noduli in substantial amounts. These initial studies provide evidence that the changes in the glomerular matrix in diabetic nephropathy may be divided into distinct and progressing stages of lesions. The reduced amount of HSPG even in slight, early lesions may represent the morphologic correlate to the impaired filter function of the glomerular basement membrane.     

Interstitial fibrosis in the heart: differences in extracellular matrix proteins and matrix metalloproteinases in end-stage dilated, ischaemic and valvular cardiomyopathy

AIMS: To investigate whether or not there are differences in the distribution of extracellular matrix (ECM) proteins and matrix metalloproteinases (MMPs) in end-stage heart failure underlying different cardiomyopathies. METHODS AND RESULTS: Thirty-nine explanted human hearts were investigated: 15 with dilated cardiomyopathy (DCM), 17 with ischaemic cardiomyopathy (ICM) and seven with valvular cardiomyopathy (VCM). Transmural samples from four different sites were investigated. Frozen sections were processed for immunohistochemistry for collagens type I, III, IV, laminin and fibronectin, as well as MMP-1, -2 and -9. Volume densities were determined. All ECM components were expressed more frequently in DCM than in ICM. Comparing ICM with VCM, all proteins were found more frequently in VCM than in ICM except for type III collagen, which was significantly more frequent in ICM. Comparing DCM and VCM, VCM showed significantly higher volume densities for type III collagen and laminin. MMPs showed only slight variations between the cardiomyopathies. CONCLUSION: The distribution of ECM proteins differs between DCM, ICM and VCM, which suggests that they can be morphologically discriminated by interstitial fibrosis, especially by their expression of matrix proteins.     

Characteristics of the extracellular matrix in the formation of sclerosis of the chorionic villi (immunofluorescence studies)

Distribution of the eight components of extracellular matrix in small villi of human placenta was studied with indirect immunofluorescence. Normal full-term pregnancy was found to present rough fibers and type I collagen conglomerates accumulated in the stromal center, while type III and V collagens occurred all over the villous surface. Stromal localization of type IV collagen was recorded as well as its presence in basal membranes of the epithelium and vessels. Fibronectin showed diffuse distribution concentrating along the vessels. Laminin, entactin and in lesser degree heparan sulphate proteoglycan were registered in epithelial and vascular basal membranes. Isolated sclerosis of the villi in pathological pregnancy involved stromal accumulation of type I, III collagens, small fragments of collagens type IV, V and fibronectin. Multiple sclerosis of adherent villi demonstrated hyalin-like conglomerates of various collagens and fibronectin filling up the stroma. Laminin, heparan sulphate proteoglycan and entactin were not observed at these sites.     

Enhanced bronchial expression of extracellular matrix proteins in chronic obstructive pulmonary disease

Remodeling of airways and blood vessels is an important feature in chronic obstructive pulmonary disease (COPD). By using immunohistochemical analysis, we examined bronchial expression patterns of various extracellular matrix (ECM) components such as collagens (subtypes I, III, and IV), fibronectin, and laminin beta2 in patients with COPD (forced expiratory volume in 1 second [FEV1] or=85%; n = 16) and correlated expression data with lung function. Quantitative analysis revealed enhanced levels (P < .01) of total collagens I, III, and IV in surface epithelial basement membrane (SEBM) and collagens I and III in bronchial lamina propria (P < .02) and adventitia (P < .05) in COPD. Distinct and increased (P < .05) vascular expression of fibronectin accounts for intimal vascular fibrosis, whereas laminin beta2 (P < .05) was elevated in airway smooth muscle (ASM). FEV1 values inversely correlated with collagens in the SEBM, fibronectin in bronchial vessels, and laminin in the ASM. Our data suggest that COPD exhibits increased bronchial deposition of ECM proteins that contribute to deteriorated lung function and airway remodeling.     

Cellular sources of matrix proteins in experimentally induced cholestatic rat liver

Collagens (I, III, and IV), fibronectin, and laminin were localized using the indirect immunoperoxidase technique 14 days after bile duct ligation, i.e., when extensive fibrosis and numerous neoformed bile ducts were observed. Extensive fibrous septa in enlarged portal spaces were stained for collagens I, III and IV, fibronectin, and laminin. Collagen IV and laminin were abundant around proliferative bile ducts. In addition, collagen IV was nearly continuous in the sinusoids. At the ultrastructural level, antigens were localized in the endoplasmic reticulum of several liver cell types. In portal spaces, bile duct cells and cells that form the transitional canal of Hering were strongly labelled for basement membrane components, particularly laminin, but not for collagens I and III and fibronectin, which were abundant in fibroblast-like cells. Inside the lobule, only Ito cells and, to a lesser extent, endothelial cells contained collagens, fibronectin, and laminin. Ito cells were found to be heavily stained for collagens III and IV, and laminin. Except for fibronectin, which was always abundant, precursors of extracellular matrix proteins were only slightly detectable in the endoplasmic reticulum of some hepatocytes, particularly those located close to altered areas. This study demonstrates that experimental extrahepatic cholestasis in the rat induces periportal fibrosis and continuous deposition of collagen IV in the sinusoids. Several cell types participate in the formation of extracellular matrix components, particularly bile duct cells and Ito cells, with a possible involvement of hepatocytes, thus suggesting that cholestasis provokes changes in the pattern of matrix protein production in liver cells.     

A key role for fibronectin in the sequential binding of native dsDNA and monoclonal anti-DNA antibodies to components of the extracellular matrix: its possible significance in glomerulonephritis.

The interactions of DNA, monoclonal anti-DNA autoantibodies and isolated purified components of the extracellular matrix (ECM) were studied in a solid phase model system. Binding of DNA to each of the components was assessed using monoclonal antibody and enzyme conjugated antiglobulin in direct binding and inhibition assays. Each of the genetically distinct collagens (Types I-IV), proteoglycan monomer and laminin, bound ssDNA, but dsDNA bound significantly only to fibronectin. When used in an inhibition system, fibronectin linked DNA and anti-DNA antibodies to the collagens; it had a differential effect on the binding of ssDNA and dsDNA to a Type IV collagen matrix, the most striking feature being a 100 fold increase in dsDNA binding to Type IV collagen in the presence of fibronectin. It is likely that fibronectin binds dsDNA to collagen by separate binding domains for these molecules, and that this may be involved in the deposition of DNA in kidneys in some forms of glomerulonephritis.     

Localization of extracellular matrix components in developing mouse salivary glands by confocal microscopy.

The importance of the extracellular matrix (ECM) in epithelial-mesenchymal interactions in developing organisms is well established. Proteoglycans and interstitial collagens are required for the growth, morphogenesis, and differentiation of epithelial organs and the distribution of these molecules has been described. However, much less is known about other ECM macromolecules in developing epithelial organs. We used confocal microscopy to examine the distribution of laminin, heparan sulfate (BM-1) proteoglycan, fibronectin, and collagen types I, IV, and V, in mouse embryonic salivary glands. Organ rudiments were isolated from gestational day 13 mouse embryos and cultured for 24, 48, or 72 hours. Whole mounts were stained by indirect immunofluorescence and then examined using a Zeiss Laser Scan Microscope. We found that each ECM component examined had a distinct distribution and that the distribution of some molecules varied with culture time. Laminin was mainly restricted to the basement membrane. BM-1 proteoglycan was concentrated in the basement membrane and also formed a fine network throughout the mesenchyme. Type IV collagen was mainly located in the basement membrane of the epithelium, but it was also present throughout the mesenchyme. Type V collagen was distributed throughout the mesenchyme at 24 hours, but at 48 hours was principally located in the basement membrane. Type I collagen was distributed throughout the mesenchyme at all culture times, and accumulated in the clefts and particularly at the epithelial-mesenchymal interface as time in culture increased. Fibronectin was observed throughout the mesenchyme at all times.     

Localization of extracellular matrix components in developing mouse salivary glands by confocal microscopy

The importance of the extracellular matrix (ECM) in epithelial-mesenchymal interactions in developing organisms is well established. Proteoglycans and interstitial collagens are required for the growth, morphogenesis, and differentiation of epithelial organs and the distribution of these molecules has been described. However, much less is known about other ECM macromolecules in developing epithelial organs. We used confocal microscopy to examine the distribution of laminin, heparan sulfate (BM-1) proteoglycan, fibronectin, and collagen types I, IV, and V, in mouse embryonic salivary glands. Organ rudiments were isolated from gestational day 13 mouse embryos and cultured for 24, 48, or 72 hours. Whole mounts were stained by indirect immunofluorescence and then examined using a Zeiss Laser Scan Microscope. We found that each ECM component examined had a distinct distribution and that the distribution of some molecules varied with culture time. Laminin was mainly restricted to the basement membrane. BM-1 proteoglycan was concentrated in the basement membrane and also formed a fine network throughout the mesenchyme. Type IV collagen was mainly located in the basement membrane of the epithelium, but it was also present throughout the mesenchyme. Type V collagen was distributed throughout the mesenchyme at 24 hours, but at 48 hours was principally located in the basement membrane. Type I collagen was distributed throughout the mesenchyme at all culture times, and accumulated in the clefts and particularly at the epithelial-mesenchymal in terface as time in culture increased. Fibronectin was observed throughout the mesenchyme at all times.© Willey-Liss, Inc.     

Modulation of human mesangial cell behaviour by extracellular matrix components--the possible role of interstitial type III collagen.

We have investigated the effects of various extracellular matrix (ECM) components on the behaviour of human mesangial cells (HMC) in a gel culture system using a modified MTT assay method. When cultured on a reconstituted basement membrane, Matrigel (M gel), HMC aggregated and formed isolated colonies initially, then extended an array of cell processes to form a dendritic network structure and proliferated very slowly as the culture period progressed. On type I collagen gel (CI gel), however, HMC developed elongated bipolar shapes, migrated into the gel, and showed rapid cell growth. Next, separate ECM components, such as type III and IV collagens, laminin, heparin and heparan sulphate, were incorporated into CI gel and HMC proliferation was assessed. Although attachment of HMC to each gel did not differ significantly, HMC proliferation was inhibited markedly on gels containing type III collagen, heparin and heparan sulphate; type IV collagen suppressed HMC proliferation slightly; and laminin had no significant effect. These data suggest that interstitial type I and III collagens, which are often observed in diseased glomeruli, as well as the basement membrane components, may play important roles in the regulation of HMC proliferation under pathophysiological conditions in vivo. We conclude that HMC behaviour is affected by the surrounding ECM constituents, which appear to function as a refined modulator.     

Binding of Haemophilus ducreyi to extracellular matrix proteins

We developed an enzyme-linked immunosorbent assay-based assay to assess Haemophilus ducreyi binding to extracellular matrix (ECM) proteins. H. ducreyi 35000HP bound to fibronectin, laminin, and type I and III collagen but not to type IV, V, or VI collagen or elastin. Isogenic strains with mutations in ftpA or losB bound as well as the parent, suggesting that neither pili nor full-length lipooligosaccharide is required for H. ducreyi to bind to ECM proteins.     

The hepatic extracellular matrix. II. Electron immunohistochemical studies in rats with CCl4-induced cirrhosis

Monospecific antibodies against collagen types I, IV, fibronectin, and laminin were used to characterize the hepatic extracellular matrix in CCl4-induced cirrhosis. Of the four antigens studied, fibronectin was the first (2 weeks) to be deposited in Disse's space. Synthesis of fibronectin by hepatocytes was demonstrable by 3 weeks. This increased synthesis and deposition of fibronectin continued throughout the cirrhotic process. Type I collagen was deposited in the same areas as fibronectin, but there was a delay of 2 weeks between fibronectin deposition and the subsequent type I collagen deposition. Like fibronectin, type I collagen was localized in the rough endoplasmic reticulum of hepatocytes, but unlike fibronectin type I collagen synthesis was restricted to hepatocytes near zones of necrosis. Type I collagen and fibronectin synthesis were demonstrable only in hepatocytes. Type IV collagen deposition was noticeable after 3 to 4 weeks of CCl4 administration and continued throughout the cirrhotic process. Laminin deposition was delayed, with regard to type IV collagen, by 1 to 2 weeks. Except for this time lag, both basement membrane components codistributed in the space of Disse and were synthesized by the same cells: endothelial, smooth muscle, and Ito cells. The deposition of these two basement membrane components culminated with the formation of continuous endothelial basement membranes. The four extracellular matrix components studied were synthesized and secreted by resident cells of the normal liver. It is proposed that fibronectin deposition in the space of Disse, modulating collagen deposition, may be the crucial event in the cirrhotic process. The interposition of basement membranes between plasma and hepatocytes may have profound effects on hepatic systemic functions.