The hepatic extracellular matrix. I. Electron immunohistochemical studies in normal rat liver

Monospecific antibodies directed against fibronectin, type I collagen, and two basement membrane components, laminin and type IV collagen, were localized in normal rat liver by light and electron microscopy immunohistochemistry. Type I collagen was found in the liver capsule, protal stroma, and in Disse's space where it was often in direct contact with the hepatocyte plasmalemma; along the sinusoidal wall, type I collagen was more abundant at points of branching or inflexion. Collagen type IV was found in all basement membranes: ductal, neural, and vascular. In addition, small, discrete, discontinuous, deposits of type IV collagen were found along the entire length of the sinusoid. Laminin codistributed with type IV collagen in all basement membranes but was not found in the sinusoidal wall. The structural glycoprotein, fibronectin, was found in the liver capsule and portal stroma but not in basement membranes. However, fibronectin was found in direct contact with the hepatocytes microvilli forming an almost continuous structure; it was the most prominent component of the extracellular matrix in Disse's space. These findings provide a new image of the Disse's space. Rather than being an empty space, as suggested by classic electron microscopy, it was found to contain an extracellular matrix with several unique features: type I collagen, in direct contact with hepatocytes and endothelial cells, formed the scaffold of the hepatic lobule. Type IV collagen was found "free," not associated with laminin and not forming part of a basement membrane. Hepatocytes and endothelial cells lacked a basement membrane but were separated by an extracellular matrix containing predominantly fibronectin, some type I collagen, and occasional spotty deposits of type IV collagen. Future studies of the physiology and pathology of the hepatic sinusoid will have to take into account this unique extracellular matrix.     

Extracellular matrix synthesis by undifferentiated childhood tumor cell lines.

The authors have examined extracellular matrix (ECM) biosynthesis by small round cell tumors of childhood. Basal lamina (laminin and Type IV collagen) and stroma (collagens I, III, and V and fibronectin) constituents were studied. It was found that these tumors synthesize ECM in characteristic patterns. Five Ewing's sarcomas variably synthesized small amounts of all ECM constituents except Type V collagen. All eight neural tumors (neuroblastoma and primitive neural tumors) synthesized fibronectin (unlike some Ewing's sarcomas), as well as laminin and Type IV collagen (2 cases lacked Type IV collagen synthesis). No stromal (I/III) collagen synthesis was observed by neural tumors. All soft tissue sarcomas except an embryonal rhabdomyosarcoma synthesized stromal collagens and often laminin or fibronectin as well. Lymphomas synthesized no ECM of any kind. The synthesis of stromal collagens by sarcomas but not neural tumors serves to distinguish these two tumor types, especially Ewing's sarcoma from neuroblastoma. The presence of any ECM synthesis excludes lymphoma from diagnostic consideration.     

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.     

Components of subendothelial aorta basement membrane. Immunohistochemical localization and role in cell attachment

Cryosections of fetal and adult bovine aorta were stained with purified, cross-absorbed antibodies against various connective tissue components. The antibodies to the basement membrane components, laminin, heparan sulfate proteoglycan, and type IV collagen, gave a sharp reaction in the subendothelial layer. Antibodies against type III procollagen showed a broad endothelial staining, and staining was also seen in the media layer. A similar staining reaction was seen with antibodies against fibronectin. Bovine fetal aortic endothelial (BAE) cells were isolated and cultured in vitro. The cells became stained by the indirect immunofluorescence method with antibodies against laminin and heparan sulfate proteoglycan and also with antibodies against types III and IV collagen and type I procollagen, as in previously reported experiments. The attachment properties of endothelial cells to the same extracellular matrix components were also studied. BAE cells became attached most readily to surfaces coated with fibronectin or type III or type IV collagen. Laminin and collagen types I and V served as less effective substrates. Attachment to heparan sulfate proteoglycan was slowest of the tested components. The results of the study demonstrate that the BAE cells are associated with basement membranes in vivo. The BAE cells in culture produced interstitial connective tissue components in addition to basement membrane components and showed no clear specific preference in their attachment to any of these.     

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.     

Differential expression of basement membrane collagen in membranous nephropathy.

Membranous nephropathy (MN) is characterized by subepithelial immune complex formation and progressive thickening of the glomerular basement membrane (GBM). Kidney tissues from 21 patients stratified according to morphology (stage I: 5 patients; stage II: 5 patients, stage III: 11 patients) were studied by immunohistochemical techniques using antibody probes to matrix components of recently described (novel) chains of type IV collagen [alpha 3(IV)NC, alpha 4(IV)NC, Alport antigen] and of traditional type IV collagen [alpha 1(IV)NC, alpha 2(IV)NC, 7S(IV), triple helix]; as well as laminin B2, nidogen and fibronectin. In Stage I, there were no detectable changes when compared with normal tissue. In Stage II and early Stage III, the subepithelial projections of GBM (spikes) and the thickened GBM consisted predominantly of the novel type IV collagen chains as well as laminin B2 and nidogen, with no detectable changes in traditional type IV collagen. In late Stage III, an increase in the latter was observed in the subendothelial region of the thickened GBM with narrowing of the capillary lumen. At this stage, there was close apposition of novel and traditional type IV collagen molecules. The expression of these two groups of molecules is spatially and temporally distinct during the evolution of MN. It is hypothesized that immune complex formation in the subepithelial region of the GBM leads to increased formation of the novel type IV collagen network by visceral epithelial cells resulting in the formation of spikes and thickening of GBM between and surrounding immune deposits. These changes precede and are distinct from detectable alterations in traditional type IV collagen. With progression and time, the deposits become embedded in the novel collagen network and increased subendothelial formation of traditional type IV collagen molecules occurs with narrowing of the capillary lumen.     

Extracellular matrix in hepatoblastoma: an immunohistochemical investigation

Eleven hepatoblastomas of various subtypes and normal liver tissue were investigated with antibodies against collagen types I-VI, laminin, fibronectin and endothelial and macrophage-associated antigens. Epithelial hepatoblastoma cells, unlike non-neoplastic hepatocytes, exhibited intracellular immunoreactivity for various extracellular matrix proteins (depending on the subtype: laminin, fibronectin and collagen types III, IV and V). The intracellular expression of extracellular matrix proteins by the tumour cells increased from the fetal subtype, through the embryonal subtype, to the small cell subtype. The epithelial tumours exhibited sinusoid-like blood vessels in numbers that varied according to the subtype. These contained Kupffer cells and exhibited greater amounts of the basement membrane components collagen type IV and laminin in the perisinusoidal space than those in the normal liver. The small cell hepatoblastoma exhibited smaller numbers of sinusoids, pronounced intracellular expression of extracellular matrix proteins and large numbers of fibres immunoreactive for collagen type III. In the mixed hepatoblastomas, the extracellular matrix of the osteoid was most strongly immunoreactive for collagen type I and that of the spindle cell areas for collagen type III.     

Collagen and fibronectin of the liver in children with congenital fibrosis, an extrahepatic portal circulation block and post-hepatitis cirrhosis (an immunohistochemical study)

Immunofluorescence techniques were used to examine the distribution of Types I, III, IV and V collagen and fibronectin in the liver biopsy specimens from children with congenital liver fibrosis (CLF), extrahepatic portal blood circulation block, and cirrhosis developed following viral hepatitis. Both common patterns and characteristic features of the development of sclerotic processes were established. The common feature is the development of periportal connective tissue (CT) fibrosis mainly at the expense of Types I, III and V collagen and the accumulation of Types I, III, IV, V collagen and fibronectin in the walls of sinusoids during their "collagenization". The distinctive characteristic of posthepatic cirrhosis is the location of fibronectin and Type IV collagen in fibrous CT. Characteristic of CLF is high fibronectin concentrations in the areas of CT neoplasms along the periphery of portal tracts.     

Mesangial cell hillocks. Nodular foci of exaggerated growth of cells and matrix in prolonged culture.

To examine the capability of glomerular mesangial cells (MCs) to produce extracellular matrix, the authors studied MCs in culture by light and electron microscopy as well as immunocytochemistry. MCs were obtained from isolated rat glomeruli and maintained up to 12 weeks in medium containing 20% fetal calf serum. MC outgrowth of primary culture and of up to three subcultures showed characteristic organization consisting of bands of elongated or stellate intertwined cells. After confluency at 10-16 days, MCs continued to grow in irregular multilayers. MCs produced extracellular matrix material within 2-4 days after plating, and large amounts of matrix accumulated with time. By 2-3 weeks, foci of exaggerated MC proliferation, matrix secretion, and necrotic cell debris formed nodular protrusions, which gradually produced large hillocks. Immunocytochemical studies of MC outgrowths were performed on culture plates or on sectioned material with the use of specific rabbit polyclonal antibodies to isolated matrix proteins and FITC-conjugated, affinity-purified second antibodies. Within 3 days of culture, MCs elaborated fibronectin and collagen Types I, III, IV, and V. With time, strands of matrix, notably in the central mass of hillocks, stained extensively for these constituents. Staining for laminin was less pronounced. Smooth muscle cell myosin was regularly found on distinct intracellular fibrils and in the extracellular material of hillocks. Electron microscopy revealed the hillocks to be composed of elongated cells on the surface and stellate cells intermingled with matrix and necrotic cell debris in the core. The results show that proliferating MCs can be maintained in homogeneous culture for a prolonged time period. MCs produce large amounts of the extracellular matrix proteins (Type IV and V collagen, fibronectin, laminin), which are found in normal glomeruli. Cultured MCs also produce interstitial collagen Types I and III. MC hillocks show the nodular accumulation of matrix similar to that seen in the mesangium of diseased glomeruli. It is concluded that the in vitro model of prolonged MC outgrowth may facilitate the investigation of factors that govern mesangial matrix production. Such a model could be used in examining the response of the mesangium to defined inflammatory or metabolic stimuli.     

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.     

Endothelial cell proliferation during angiogenesis. In vitro modulation by basement membrane components

Modulation of the behavior of microvascular endothelial cells during angiogenesis has been observed to correlate with changes in the extracellular matrix. These reports prompted a comparison of the growth of microvascular endothelial cells on monolayers of various matrix components in vitro. Over a 5 day period, the proliferation of these cells was significantly greater on laminin than on either plasma fibronectin, the interstitial collagen types I and III, or on the basement membrane collagen type IV. Proliferation of the microvascular endothelial cells was compared with that of bovine aortic endothelial cells and bovine aortic smooth muscle cells on the same matrices. All three cell types grew significantly more rapidly on laminin than on fibronectin. The aortic endothelial cells differed from their microvascular counterparts in that the growth of these large vessel endothelial cells on the collagenous matrices (types I and III, or type IV) was not significantly different from that observed for laminin, but was greater than the relatively slow growth seen on plasma fibronectin. Further comparison of the growth of the microvascular endothelial cells on the two basement membrane components, laminin and type IV collagen, demonstrated that the growth of these cells on laminin can be modulated by the presence of type IV collagen. This was true either if the two matrices were combined as a mixed layer, or if the laminin was specifically bound to a layer of type IV collagen, more closely simulating the distribution of these molecules in a basement membrane. Examination by immunoperoxidase of in vivo model of neovascularization in the murine cornea revealed a temporally staggered appearance of basement membrane components. The appearance of laminin was found to occur throughout the newly formed vessels, as well as in individual cells at the migrating, proliferating tips. In contrast, the appearance of type IV collagen correlated with lumen formation and was not detected at the vessel tips. The results of this study suggest that the temporally ordered synthesis of specific matrix components plays a significant role in orchestrating the growth and differentiation of endothelial cells during the highly integrated set of responses known as angiogenesis.     

Alterations in extracellular matrix components and integrins in patients with preeclamptic nephropathy

The glomerular features of patients with preeclapsia consist of swelling of endothelial cells, subendothelial deposits of incompletely defined material, and thickening of the capillary walls. These abnormalities are thought to resolve in the postpartum period. The distribution of extracellular matrix (ECM) components and integrins was investigated in 10 such patients. Frozen sections and paraffin-embedded sections were stained with antibodies to type IV collagen, laminin (LN), fibronectin (FN), vitronectin (VN), tenascin (TN), fibronectin receptor (FNR), and vitronectin receptor (VNR). In preeclamptic nephropathy, the accumulation of type IV collagen, LN, FN, TN, and FNR was observed in the thickened capillary walls, particularly in the subendothelial layer and, to some extent, in the mesangium. However, deposits of VN were sparse and the distribution of VNR was similar to that in normal kidney. In segmental sclerotic lesions, the amounts of type IV collagen, LN, FN, VN, and TN were increased, whereas those of FNR and VNR were markedly decreased. These results suggest that the materials deposited in the subendothelial space consist of ECM components as well as of plasma-derived proteins, and that the deposition of ECM components and of FNR may be involved in the development and the reparative process of the characteristic glomerular lesions. The formation of sclerotic lesions was linked to the accumulation of ECM components, but not to an interaction with integrins.     

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.     

Extracellular matrix proteins (fibronectin, laminin, and type IV collagen) bind and aggregate bacteria.

The normal microbial colonization of sites in the body's tissues by certain bacteria requires that the bacteria first bind to extracellular secreted constituents, cell-surface membranes, or cell matrixes. This study examines two interactions of a variety of bacteria with the cell matrix noncollagenous proteins fibronectin and laminin and with basement membrane (Type IV) collagen. Adherence of bacteria to matrix proteins coated on tissue culture wells was examined with the use of radiolabeled bacteria. Staphylococcus aureus, Streptococcus pyogenes, and Streptococcus sanguis bound well to fibronectin, laminin, and Type IV collagen, whereas a variety of gram-negative organisms did not bind. The interaction of soluble laminin, fibronectin, and Type IV collagen with bacteria was monitored by nephelometry with the use of a platelet aggregometer. S. aureus aggregated in response to fibronectin, laminin, or Type IV collagen. In contrast, gram-negative organisms did not aggregate with these proteins. It appears that fibronectin, laminin, and Type IV collagen can bind and aggregate certain gram-positive bacteria, and this binding is dependent on the surface characteristics of the organism. These adhesion molecules may play a role in the normal colonization of sites by microorganisms and in invasion during infections.     

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.     

Hepatocellular carcinoma developed on noncirrhotic livers. Sinusoids in hepatocellular carcinoma

In hepatocellular carcinoma, there is modification of cell-to-cell and cell-to-extracellular matrix interactions. Two cases of well-differentiated hepatocellular carcinoma that developed in noncirrhotic livers were explored by light and electron microscopy on perfusion-fixed liver biopsy specimens. In addition, immunocytolocalization of collagen types I, III, and IV, laminin, and fibronectin was assessed. The main features included the following: absence of collagen staining inside the tumor with Sirius red; decrease of collagen types I and III and the increase of collagen type IV, laminin, and fibronectin; widening of Disse's spaces containing numerous, discontinuous, and thick fragments of basement membrane-like material piled up beneath endothelial cells and around perisinusoidal cells; transformation of perisinusoidal cells into cells with the characteristics of fibroblasts and myofibroblasts; decreased numbers of fenestrae for endothelial cells with processes often overlapping and attached with tight junctions; and rarefaction of Kupffer's cells. Expression of cellular and extracellular material abnormalities are related to the tumor differentiation. The study of these abnormalities may have implications in prognosis.     

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.     

Distribution of the extracellular matrix components in human glomerular lesions

Most glomerular pathologies are associated with alterations of the matrix compartment. Using reagents directed against the α/α2 and α3 chains of type IV collagen [α1/α2(IV), α3(IV)], laminin, heparan sulphate proteoglycan (HPG), fibronectin, collagen I, and collagen III, we investigated the modifications of the glomerular matrix components in several human glomerular lesions compared with normal kidney. In type I membranous glomerulo-nephritis (MGN) (nine cases), we did not observe alterations in the matrix component distribution. In MGN types II and III (five cases), the spikes and chainettes were made of the α3(IV) chain, laminin, and HPG, while the α1/α2(IV) chains were localized along the subendothelial side of the glomerular basement membrane (GBM). In focal and segmental glomerulosclerosis (six cases), fibronectin, α1/α2(IV) chains, laminin, and small amounts of interstitial collagens were detected within the collapsed capillary loops; the newly formed matrix material between the podocytes and the GBM contained the α1/α2(IV) chains, laminin, and HPG but not the α3(IV) chain. In crescentic glomerulo-nephritis (six cases), fibronectin was the most abundant and, in purely cellular crescents, the unique component. A basement membrane-like network containing laminin, HPG, α1/α2(IV) chains, and interstitial collagens developed in a second step between the crescent cells. Interstitial collagens were present in the crescent framework, even when the integrity of Bowman's capsule was preserved. In membranoproliferative glomerulonephritis (five cases), we observed strong accumulation of fibronectin in the thickened mesangial spaces together with accumulation of laminin, α1/α2(IV) chains, and HPG; type I collagen was also present in the central part of the mesangial areas. This study shows that each glomerular lesion is characterized by particular alterations of the matrix components.     

The extracellular matrix in "sclerosing" follicular center cell lymphomas: an immunohistochemical and ultrastructural study

"Sclerosis" is frequently seen in follicular center cell (FCC) lymphomas. The mechanism of its deposition, as well as its composition and significance, are unknown. Several clinical studies have suggested that the course of these lymphomas is more indolent than that of lymphomas of the same histologic type without sclerosis. Nine immunologically characterized cleaved FCC lymphomas with sclerosis and 14 reactive lymph nodes with follicular hyperplasia were investigated by special staining methods, electron microscopy, and immunohistochemical studies with antibodies to types I, III, IV, and V collagen, laminin, and fibronectin. The sclerotic tissue in FCC lymphomas stained uniformly with periodic acid-Schiff (PAS) and Masson's stain, with the patterns ranging from delicate filamentous strands to dense doubly refractile bands. Ultrastructurally, the bands of connective tissue were continuous with the adventitia of vessels and composed of varying amounts of banded collagen (types I and III) admixed with filamentous and flocculent material. In all cases the neoplastic lymphocytes were separated from the extra-cellular matrix by fibroblasts and myofibroblasts with long cell processes. Immunohistochemical studies demonstrated intense staining of sclerotic bands with antibodies to fibronectin and type I collagen and, usually, weaker marking with antibodies to types III and V collagen. No significant staining of sclerotic bands was found with antibodies to type IV collagen or with laminin. Weak pericellular staining for type V collagen was present in eight of nine lymphomas and half of the control lymph nodes. These studies suggest that the increased amounts of extracellular matrix in cleaved FCC lymphomas are produced primarily by fibroblasts and myofibroblasts and represent predominantly fibronectin and types I, III, and V collagen. The composition of the sclerotic areas of FCC lymphomas is similar immunohistochemically to that of the capsule and trabeculae of reactive lymph nodes, which are also intimately associated with fibroblasts and myofibroblasts.     

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.