Expression of tenascin in lymphocytic autoimmune thyroiditis.

AIMS: To study the distribution of tenascin by immunocytochemistry in autoimmune diseases of the thyroid. METHODS: Thyroids from patients with inflammatory lesions of the thyroid (lymphocytic thyroiditis Hashimoto, Grave's disease, thyroiditis DeQuervain) were studied by immunocytochemistry using antibodies against tenascin, collagen III, and collagen IV. RESULTS: In autoimmune lymphocytic thyroiditis Hashimoto there was a characteristic corona-like staining pattern of tenascin around all activated lymph follicles with germinal centres. This staining pattern contrasted with the immunoreactions for collagen III and IV, which were not enhanced in the perilymphofollicular interstitium. In cases of thyroiditis DeQuervain the areas of early and ongoing fibrosis showed some diffuse staining for tenascin and for collagen III. Enhanced diffuse immunostaining for collagen IV in the perivascular and interfollicular interstitium was present in cases of Grave's disease. In Grave's disease no characteristic immunoreaction was detectable for tenascin. CONCLUSIONS: The corona-like expression of tenascin around lymphofollicular infiltrates is distinctive of cases of lymphocytic thyroiditis. A similar staining pattern for tenascin has been reported in lymphoid hyperplasia of the thymus associated with myasthenia gravis, another autoimmunological disorder. There are good arguments that the activation and infiltration of lymph follicles in the thyroid during the course of autoimmune diseases lead to stimulation and activation of the surrounding mesenchyme producing tenascin as part of the extracellular matrix.     

Splenic adherent cells, stimulated in vitro, induce the reactive formation of lymphoid follicles and germinal centres in draining lymph nodes after subcutaneous transfusion into syngeneic mice

The reactive formation of lymphoid follicles and germinal centres in lymph nodes, induced by subcutaneous transfer of in vitro activated splenic adherent cells into syngeneic mice, were studied. Adherent cells were obtained by incubating spleen cell suspensions for 24 h and activated by incubating for 1 h in the medium containing keyhole limpet haemocyanin (KLH) absorbed onto alumina. Some of the treated adherent cells were irradiated with 10 Gy x-rays, while others were either not stimulated or were stimulated with alumina-KLH but killed by repeated freezing and thawing. Examination of adherent cell smears immunostained with antibodies against, F4/80, Mac-1, Mac-2 and NLDC-145 indicated that many adherent cells displayed macrophage markers but few displayed the interdigitating cell marker. Animals transfused with KLH-treated adherent cells with or without irradiation showed a marked increase in the number of lymphoid follicles and germinal centres in draining lymph nodes, whereas those transfused with adherent cells which had not been KLH-treated or which had been killed after KLH treatment displayed no significant change in the number of follicles. These results were interpreted as indicating that following transfusion, antigen-activated adherent macrophages migrated into the draining lymph nodes and induced the reactive formation of lymphoid follicles and germinal centres outside preexisting follicles.     

Immunohistochemical study of the reticular and vascular network of mouse lymph node using vibratome sections

The function of lymph nodes is greatly influenced by their unique microanatomy, in which distinct subpopulations of cells are compartmentalized by a meshwork of reticular cells and fibres, specialized blood and lymphatic vessels and nerves. Using antibodies against extracellular matrix (ECM) proteins (fibronectin, collagen IV and laminin), proteoglycan (perlecan), and a fibroblastic marker (ERTR-7), the distribution and molecular organization of the system of reticular fibres was investigated by three-dimensional (3D) reconstruction methods. Fibronectin, collagen IV and laminin are restricted to reticular fibres and have a similar distribution pattern, whereas perlecan is limited to the vascular system of the lymph node. Various compartments of the lymph node, such as the B-cell follicle, paracortex (including the high endothelial venules and paracortical cord), and medulla have been reconstructed to visualize their vasculature with respect to B and T cells. Since the morphology of lymph nodes may change significantly in pathological conditions, different compartments of reactive lymph node (after low-dose Listeria monocytogenes infection), especially germinal centres, were also investigated. The data presented here should facilitate our understanding of the 3D organization of non-immune cell components of lymph nodes, which is crucial for cell adhesion, migration, activation, and differentiation in normal and pathological conditions.     

Dendritic reticulum cells in reactive lymph nodes and tonsils: an immunohistological study

There has recently been much interest in the patterns of follicular dendritic reticulum cells (DRC) in pathological lymph nodes, particularly in relation to the phenomenon of DRC break-up (thought to be pathognomonic of AIDS-related lymphadenopathies) and to progressive transformation of germinal centres (as a possible precursor of lymphocyte predominant Hodgkin's disease). In the present study we have immunostained twenty-nine reactive lymph nodes and five tonsils with monoclonal antibody R4/23 (DAKO-DRC) in order to evaluate the frequency of such changes in lymphoid tissue unaffected by AIDS or Hodgkin's disease. Most of the specimens contained typical secondary follicles with clearly defined germinal centres and mantle zones. There were two variants in lymph nodes showing follicular hyperplasia characterized by (i) progressive transformation of germinal centres and (ii) inclusions of nests of small lymphocytes within germinal centres. In each of these types of follicles the compact evenly-distributed meshwork of DRCs, as previously described, was seen. However there were considerable variations in DRC meshwork in each category (the pattern could not be predicted from the morphology) with examples in all three of the DRC break-up previously considered specific for the AIDS related lymphadenopathy. Since none of the lymph nodes and tonsils studied had any known relationship to either Hodgkin's disease or AIDS it is argued that none of the changes in the DRC meshwork observed are specific for these conditions.     

Acid cysteine-proteinase inhibitor, a new characteristic of reticulum cells in human lymphoid secondary follicles

Reactive lymph nodes, palatine tonsils and thyroid tissues infiltrated with reactive lymphatic tissue were studied for the presence of immunoreactive acid cysteine-proteinase inhibitor (ACPI). A positive reaction for ACPI was found in germinal centres in all the above tissue types. The morphology and distribution of the positive cells indicated immunoreactivity in the dendritic reticulum cells (DRC). A positive reaction was also found in starry sky cells when a strong starry sky reaction was present in germinal centres. ACPI-positive cells of dendritic appearance were also found outside the secondary follicles in tonsillar tissue from cases of chronic or recurrent tonsillitis, especially between the follicles and the crypt epithelium, in some lymph nodes exhibiting a strong follicular reactive hyperplasia and in thyroid tissue in one case of Hashimoto's thyroiditis. A close anatomical and morphological relationship is pointed out between ACPI reactive dendritic cells and epithelial tissue. This is especially true of the tonsillar crypt epithelium and adjacent lymphoid secondary follicles. The tonsillar crypt epithelium sometimes formed a loose, web-like structure with enmeshed lymphoid cells, even reminiscent of dendritic compartmentalization of lymphoid secondary follicles. The results suggest that ACPI-immunoreactivity of DRC could be a function of the outer membrane of dendritic processes, and thus could be in some way a parallel phenomenon to the morphological expression of the well-established function of DRC in capturing antigen and immune complexes.     

An extracellular matrix infrastructure provides support for murine secondary palatal shelf remodelling.

A crucial part of secondary palate morphogenesis is the movement of the palatal shelves from an initial vertical position on either side of the tongue to a final horizontal one above it to achieve palate closure. The immunocytochemical localization of extracellular matrix (ECM) molecules in the palatal shelf during this remodelling and reorientation revealed the existence of an ECM infrastructure within the mesenchyme. The major components of this infrastructure were collagen III, fibronectin, and hyaluronate (HA). With remodelling, HA's domain within the mesenchyme was expanded, whereas those of fibronectin and collagen III became more circumscribed. The expansion of an HA-rich matrix within the mesenchyme is thought to be crucial for palatal reorientation. The results of this study suggest that, as this expansion occurs, it is modulated by collagen and fibronectin components of the ECM infrastructure. Prior to shelf remodelling, this infrastructure may be anchored by a specialized region of the midoral epithelial-mesenchymal interface and the subjacent mesenchyme which is characterized by the unique distribution of collagen III, fibronectin, and tenascin. The midoral palatal epithelium also may play a role in directing shelf expansion. This epithelial region undergoes changes in cell packing and epithelial cell layering that correlate with shelf remodelling. These changes occur concomitantly with changes in the expression of collagen III, collagen IV, and laminin within the underlying basement membrane. The localization and patterning of tenascin within the developing palate suggests that it not only contributes to the postulated anchoring structure of the midoral epithelial-mesenchymal region, but also plays a role in the determining the fate of the medial edge epithelial cells during the final stage of palate closure.     

An extracellular matrix infrastructure provides support for murine secondary palatal shelf remodelling

A cricial part of secondary palate morphogenesis is the movement of the palatal shelves from an initial vertical position on either side of the tongue to a final horizontal one above it to achieve palate closure. The immunocytochemical localization of extracellular matrix (ECM) molecules in the palatal shelf during this remodelling and reorientation revealed the existence of an ECM infrastructure within the mesenchyme. The major components of this infrastructure were collagen III, fibronectin, and hyaluronate (HA). With remodelling, HA's domain within the mesenchyme was expanded, whereas those of fibronectin and collagen III became more circumscribed. The expansion of an HA-rich matrix within the mesenchyme is thought to be crucial for palatal reorientation. The results of this study suggest that, as this expansion occurs, it is modulated by collagen and fibronectin components of the ECM infrastructure. Prior to shelf remodelling, this infrastructure may be anchored by a specialized region of the midoral epithelial-mesenchymal interface and the subjacent mesenchyme which is characterized by the unique distribution of collagen III, fibronectin, and tenascin. The midoral palatal epithelium also may play a role in directing shelf expansion. This epithelial region undergoes changes in cell packing and epithelial cell layering that correlate with shelf remodelling. These changes occur concomitantly with changes in the expression of collagen III, collagen IV, and laminin within the underlying basement membrane. The localization and patterning of tenascin within the developing palate suggests that it not only contributes to the postulated anchoring structure of the midoral epithelial-mesenchymal region, but also plays a role in the determining the fate of the medial edge epithelial cells during the final stage of palate closure.© Willey-Liss, Inc.     

Histology and immunohistochemistry of the gut-associated lymphoid tissue of the eastern grey kangaroo, Macropus giganteus

Mesenteric lymph nodes and gut-associated lymphoid tissue (GALT) from juvenile eastern grey kangaroos were investigated. The mesenteric nodes had a similar structure to that described for eutherian mammals. They contained distinct regions of medulla and cortex, with prominent follicles and germinal centres. Gut associated lymphoid tissue consisted of areas of submucosal follicles. These varied from areas of densely packed lymphocytes with darkly staining, prominent coronas to areas with no defined follicles. The distribution of T cells in these tissues was documented by use of species-crossreactive antibodies to the surface markers CD3 and CD5; B cells were identified by antibodies to CD79b. Within the lymph nodes T cells were located mainly in the paracortex and cortex, with limited numbers observed in the follicles; B cells were located on the marginal zone of the follicles. In GALT, T cells were located in the peripheral regions of the germinal centres of secondary follicles, while B cells were abundant in primary follicles. These observations are consistent with those made in a range of other marsupials (metatherian) and eutherian mammals and are indicative of the capacity to respond to antigens entering via the mouth.     

The distribution of immunoglobulin and other plasma proteins in human reactive lymph nodes

The distribution of immunoglobulin, transferrin and albumin in human reactive lymph nodes was determined by the unlabelled antibody peroxidase-antiperoxidase (PAP) method and correlated with the structure of the nodes. All the nodes contained secondary lymphoid follicles which showed polarity towards a lymph sinus, usually the marginal sinus. The lymphatic sinuses were usually dilated. Various types of reticulum cells were demonstrated effectively by the metalophil method. Intracellular and extracellular antigen was well shown in paraffin sections of tissues fixed in buffered formaldehyde containing 5 per cent. acetic acid but cryostat sections were superior for surface Ig. The lymphocyte corona of each follicle reacted for surface immunoglobulin (μ, α, δ κ and λ chains). A polyclonal population of immunoglobulin-containing cells (centrocytes, centroblasts and plasma cells) was present in the follicle centre and numerous plasma cells were often found in the interfollicular areas; each of these cells contained one heavy and one light chain. The many other sites that reacted for immunoglobulin contained not only several heavy chains and both light chains but also transferrin and albumin: these sites included lymphocyte-like cells in the interfollicular areas; histiocytic, dendritic and fibroblastic reticulum cells; clusters of lymphocytes associated with dendritic reticulum cells; clusters of lymphocytes associated with dendritic reticulum cells; the cells lining the lymphatic sinuses and the intrasinusoidal reticulum cells; endothelial cells of the high endothelial venules; “extracellular” material in the germinal centres. The lymphatic endothelium and intrasinusoidal reticulum cells differed from the other sites, however, in reacting strongly for α and J chain and very weakly for γ chain. The fact that in reactive lymphoid tissue many cells contain several plasma proteins makes it difficult to draw conclusions about the role that such cells may have in the immune system. The morphological structure and immunohistochemical findings in ractive nodes are contrasted with the findings in lymphomas.     

Recombinant vitronectin is a functionally defined substrate that supports human embryonic stem cell self-renewal via alphavbeta5 integrin

Defined growth conditions are essential for many applications of human embryonic stem cells (hESC). Most defined media are presently used in combination with Matrigel, a partially defined extracellular matrix (ECM) extract from mouse sarcoma. Here, we defined ECM requirements of hESC by analyzing integrin expression and ECM production and determined integrin function using blocking antibodies. hESC expressed all major ECM proteins and corresponding integrins. We then systematically replaced Matrigel with defined medium supplements and ECM proteins. Cells attached efficiently to natural human vitronectin, fibronectin, and Matrigel but poorly to laminin + entactin and collagen IV. Integrin-blocking antibodies demonstrated that alphaVbeta5 integrins mediated adhesion to vitronectin, alpha5beta1 mediated adhesion to fibronectin, and alpha6beta1 mediated adhesion to laminin + entactin. Fibronectin in feeder cell-conditioned medium partially supported growth on all natural matrices, but in defined, nonconditioned medium only Matrigel or (natural and recombinant) vitronectin was effective. Recombinant vitronectin was the only defined functional alternative to Matrigel, supporting sustained self-renewal and pluripotency in three independent hESC lines.     

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.     

Basement membrane components in lymphoid follicles: immunohistochemical demonstration and relationship to the follicular dendritic cell network

We analyzed the distribution of two basement membrane components, laminin and type IV collagen, in human reactive and neoplastic lymphoid follicles by using immunoenzymatic and immunofluorescence methods on serial frozen sections from 11 reactive lymph nodes, three palatine tonsils, and 11 immunophenotypically defined B cell non-Hodgkin's lymphomas. The patterns of distribution of these two antigens were compared with that of follicular dendritic reticulum cells (DRCs) as visualized by anti-DRC-1 and anti-desmoplakin 1 and 2 antibodies. Immunostaining for laminin and type IV collagen produced overlapping results. Germinal centers contained some vascular and fiber-like linear staining, but the most striking feature was the presence of a large amount of punctate-granular staining. This staining was present throughout the entire area of most of the germinal centers, although often more densely in the central areas. The stronger punctate-granular staining for laminin, type IV collagen, and desmoplakin 1 and 2 corresponded to the more densely stained areas for DRC-1. Double immunofluorescence assay demonstrated that there was a close similarity between the punctate-granular staining pattern of laminin and the dendritic network of DRC-1-positive cells. In the nine B cell lymphomas of follicular center origin in which DRCs were present, although distributed in different patterns, immunostaining for laminin and type IV collagen could be observed only in those areas showing immunoreactivity for DRC-1. The results of this study suggest that the punctate-granular staining pattern for laminin and type IV collagen is specific for the follicle. This finding may be strictly related to the follicular microenvironment because the pattern of distribution displayed by laminin and type IV collagen seems to be spatially related to the staining pattern of DRCs, as visualized by the anti-DRC-1 and desmoplakins antibodies, both in reactive and neoplastic conditions.     

Changes of glycoprotein and collagen immunolocalization in the uterine artery wall of postmenopausal women with and without pelvic organ prolapse

Pelvic organ prolapse (POP) is accompanied by an altered composition of the extracellular matrix (ECM). However, it is unclear whether the changed ECM is the cause or the consequence of POP, as stretching of the tissue may have an effect on the composition of the ECM. To address this question, we analyzed the connective tissues of the uterine artery wall of postmenopausal women with and without POP. The uterine artery wall is stretched in patients with POP, but this stretching is unlikely to cause the POP. Twenty-one women (13 with POP and 8 without POP) hospitalized for hysterectomy were included in this study. Tissue samples from the uterine artery were analyzed for collagen (types I, III, IV, V and VI) and other ECM proteins (fibronectin, laminin, tenascin, vitronectin and elastin) using immunofluorescence microscopy. Results revealed that uterine artery samples of women with prolapse showed a significantly weaker immunoreactivity to type VI collagen, vitronectin and elastin and a stronger immunostaining for type III collagen and tenascin as compared to control samples.Our results suggest that the ECM may be altered in response to mechanical stretch. Changes in the ECM composition as observed in POP may not necessarily be the reason for the development of pelvic floor relaxation in postmenopausal women.     

Adhesion of menstrual endometrium to extracellular matrix: the possible role of integrin alpha(6)beta(1) and laminin interaction

Previous in-vitro studies have shown that the endometrium preferentially adheres to the extracellular matrix (ECM) of the amnion and peritoneum. This interaction probably involves adhesion molecules, e.g. integrins. We evaluated the expression of integrins in naturally shed menstrual endometrium and the adhesion pattern of this tissue to different components of the ECM. To identify integrins and matrix components involved, blocking studies were performed. Most of the 15 menstrual tissue samples showed positive staining for each of the integrins investigated, except alpha(4)beta(1). Compared with binding to collagen IV, which was set at 100%, adhesion to collagen I was 93% (not significant), to fibronectin 87% (P < 0.05), and to laminin 74% (P < 0.05). Scanning electron micoscopy showed that endometrium adhered to laminin but hardly spread, whereas spreading was observed when layered on the other coatings. Compared with the control (which was set at 100%), incubation with 4B4, a monoclonal antibody against the integrin beta(1) subunit, showed a significant reduction of adhesion (to approximately 50%; P < 0.05) when layered on laminin and a smaller reduction (to 82-86%; P < 0.05) when layered on the other three coatings. Incubation with antibody GOH3 against integrin alpha(6)beta(1) resulted in a similar reduction in adhesion to laminin. Incubation with an RGD peptide significantly reduced adhesion (to 84%; P < 0.05) when plated on fibronectin. In conclusion, antegradely shed menstrual endometrium expresses various integrins. It shows preferential attachment to collagen IV and collagen I, when compared with fibronectin and laminin. Blockage of the integrin beta(1) subunit resulted in greatest disruption to adhesion when layered on laminin, implying that the interaction was mediated by the alpha(6)beta(1) integrin. Since this adhesion was not completely blocked, other mechanisms are likely to be involved.     

Cellular composition of follicles of follicle centre cell lymphomas in relation to germinal centres of reactive lymph nodes. A morphometrical electromicroscopical study

The cell spectrum of neoplastic and benign reactive germinal centres was determined ultrastructurally. The degree in which the cell composition found in reactive germinal centres is maintained in analogous structures of follicular lymphomas was investigated by pattern recognition methods and discriminant analysis based on the frequencies of the various lymphoid and non-lymphoid cell types. The follicular lymphomas included lymphomas with predominantly centrocytes (FCCL, Cb-cc) and lymphomas with predominantly centroblasts (FCCL, Cb). Pattern analysis of FCCL Cb, FCCL Cb-cc and reactive germinal centres indicates that FCCL Cb follicles resemble reactive germinal centres in more aspects than follicles of FCCL Cb-cc. Clear statistical differences were encountered between the frequencies of the lymphoid cell types and of the follicular dendritic and histiocytic reticulum cells in follicles of FCCL Cb-cc and FCCL Cb and reactive germinal centres. Application of a discriminant analysis using a combination of the frequency of centrocytes and follicular dendritic cells demonstrated that both types of neoplastic follicles and reactive germinal centres were correctly classified on the basis of their cell spectrum. For the three groups the most potent discriminator was the centrocyte, whereas the small and large centroblast were of less value. For discrimination between Cb-cc follicles and reactive germinal centres again the centrocyte was the most potent discriminator. Discrimination between FCCL Cb follicles and reactive germinal centres of FCCL Cb-cc follicles can be easily achieved using the frequencies of small centroblasts or centrocytes on their own. These findings indicate that (1) follicles of both FCCL Cb and FCCl Cb-cc differ greatly in the cellular composition and not only with respect to their content of centroblasts but also in their content of follicular dendritic cells and (2) they may be considered as neoplasms representing different developmental phases of germinal centres.     

Th17 cells induce ectopic lymphoid follicles in central nervous system tissue inflammation

Ectopic lymphoid follicles are hallmarks of chronic autoimmune inflammatory diseases such as multiple sclerosis (MS), rheumatoid arthritis, Sj?gren's syndrome, and myasthenia gravis. However, the effector cells and mechanisms that induce their development are unknown. Here we showed that in experimental autoimmune encephalomyelitis (EAE), the animal model of MS, Th17 cells specifically induced ectopic lymphoid follicles in the central nervous system (CNS). Development of ectopic lymphoid follicles was partly dependent on the cytokine interleukin 17 (IL-17) and on the cell surface molecule Podoplanin (Pdp), which was expressed on Th17 cells, but not on other effector T cell subsets. Pdp was also crucial for the development of secondary lymphoid structures: Pdp-deficient mice lacked peripheral lymph nodes and had a defect in forming normal lymphoid follicles and germinal centers in spleen and lymph node remnants. Thus, Th17 cells are uniquely endowed to induce tissue inflammation, characterized by ectopic lymphoid follicles within the target organ.     

Hodgkin''s disease with lymphocytic predominance, nodular type (nodular paragranuloma) and progressively transformed germinal centres—a cytohistological study

The histology, cytology, and enzyme cytochemistry of a nodular variant of Hodgkin's disease with lymphocytic predominance, called 'nodular paragranuloma', are presented. The histological features of nodular paragranuloma are compared with those of progressively transformed germinal centres, which are enlarged follicles showing a predominance of small lymphocytes and some residual germinal centre cells. Progressively transformed germinal centres are sometimes found in nonspecific lymphadenitis (reactive hyperplasia). The histological similarity and the association between lymph nodes with nodular paragranuloma and lymph nodes with progressively transformed germinal centres in the same patient at different moments or at the same time, suggest that progressively transformed germinal centres are the origin of nodular paragranuloma. Hence, it must be concluded that nodular paragranuloma takes place in B-cell areas of the lymph node, unlike the other, or at least most of the other, types of Hodgkin's disease.     

Integrin alpha2beta1 on rat myeloma cells modulates interaction of alpha4beta1 integrin with vascular cell adhesion molecule-1 but not fibronectin

It is well established that alpha2beta1 integrin functions as a receptor for collagen and laminin; whereas alpha4beta1 integrin binds fibronectin and vascular cell adhesion molecule-1 (VCAM-1). In the present study, we showed that rat myeloma YB2/0 cells constitutively expressed alpha4beta1 but not alpha2beta1 integrin. Transfection of cDNA of mouse a2 integrin subunit resulted in the expression of heterologous alpha2beta1 integrin on YB2/0 cells (YBmalpha2). The expression of alpha2beta1 conferred YBmalpha2 cells the ability to interact with collagen and laminin. In comparison with mock transfected YB2/0 cells (YBpF), YBmalpha2 cells exhibited increases in the binding and migration on VCAM-1; in contrast, both YBpF and YBmalpha2 were similar in their interactions with fibronectin or fibronectin fragment FN-40 that contains the binding site for alpha4beta1 integrin. The interaction of alpha4beta1 with VCAM-1 was further stimulated upon ligation with alpha2beta1-specific mAb. The use of specific inhibitory mAb demonstrated the role of alpha4beta1 in mediating the observed interactions with fibronectin and VCAM-1. Therefore, results show that expression of alpha2beta1 differentially regulated alpha4alpha1 integrin function by stimulating its interactions with VCAM-1 but not fibronectin. The in vivo significance of alpha2beta1 integrin expression was demonstrated by intravital videomicroscopy showing that ligation of alpha2beta1 enhanced alpha4beta1-mediated extravasation of YBmalpha2 cells in the liver.     

Expression of extracellular matrix ligands and receptors in the muscular tissue and draining lymph nodes of mdx dystrophic mice.

The mdx mouse, an animal model of Duchenne muscular dystrophy, develops an X-linked recessive inflammatory myopathy. During onset of disease and height of myonecrosis, mdx mice also display important changes in the microenvironment of lymphoid tissues. Draining lymph nodes showed reduced cellularity and atrophy accompanied by intense immunolabeling for fibronectin, laminin, and type-IV collagen. Following clinical amelioration of dystrophy, mdx mice showed enhanced cellularity and a consistent increase in the absolute numbers of CD4(+) and CD8(+) cells expressing alpha4(high) and alpha5(high) extracellular matrix receptors. Furthermore, infiltrating cells in the proximity of myonecrosis expressed alpha4, alpha5, and alpha6 integrin chains during both height of myonecrosis and muscular tissue regeneration. Such results indicate that during distinct phases of muscular dystrophy, altered expression of extracellular matrix ligands and receptors may be influencing myonecrosis by promoting adhesion and migration of mononuclear cells into the altered skeletal muscle and toward local draining lymphoid tissue.