How do lymphocytes know where to go: current concepts and enigmas of lymphocyte homing.
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Allergy and Immunology↗
Biomedical subjects
M Salmi
Publications and source records attributed to M Salmi.
Vascular adhesion protein-1 and intercellular adhesion molecule-1 mediate T-cell binding to human hepatocellular carcinoma.
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Antibodies, Monoclonal↗
Binding of malignant lymphoid cells to the white matter of the human central nervous system: role of different CD44 isoforms, beta 1, beta 2 and beta 7 integrins, and L-selectin.
Spreading of reactive and malignant lymphoid cells into the brain parenchyma requires regulated adhesion of the lymphoid cells to the parenchymal cells and/or extracellular matrix of the central nervous system. A multifunctional adhesion molecule CD44 partially mediates binding of lymphocytes to the white matter by interacting with hyaluronate. To analyze which forms of CD44 and what other adhesion molecules mediate this binding. Namalwa cells were transfected to express either standard (CD44st) or variant isoforms of CD44 containing exons v6-v10, v7-v10, and v8-v10. The binding of CD44st and CD44v6-v10 transfectants to human cerebellar white matter was tested and it was about 1.7- and 2-fold greater without and with PMA activation, respectively, compared with vector-transfected control cells. Hyaluronidase digestion of tissue sections decreased binding of CD44 expressing cells to the level of vector-transfected cells. Hermes-1, a monoclonal antibody recognizing the hyaluronate binding site of CD44, inhibited white matter adhesion of CD44v6-v10 and activated CD44st cells and binding of soluble hyaluronate to the CD44 transfectants. Transfectants also expressed beta 1, beta 2 and beta 7 integrins and L-selectin, but antibodies against these molecules did not inhibit adhesion to the white matter. These results suggest: (a) Addition of exons v6-v10 to the membrane proximal region of CD44 does not affect lymphoid cell adhesion to the white matter. (b) The only ligand of CD44 in the central nervous system (CNS) white matter is hyaluronate. (c) Additional adhesion mechanisms other than the ones analyzed above must exist.
Burkitt Lymphoma↗
Recirculation and homing of lymphocyte subsets: dual homing specificity of beta 7-integrin(high)-lymphocytes in nonobese diabetic mice.
The beta 7-integrin subunit can pair with two alpha-chains, alpha 4 and alpha E, and is expressed mainly on lymphocytes. As an alpha 4-heterodimer it binds to the mucosal addressin MAdCAM-1, thus acting as a mucosal homing receptor. As an alpha E-heterodimer it binds to E-cadherin and is mainly found on intestinal intraepithelial lymphocytes. Consequently, beta 7 is mostly expressed on lymphocytes of the mucosal immune system. To study the compartmentalization of these cells further we compared the distribution of such lymphocytes in two strains of mice (BALB/c and NOD) and found that the distribution of beta 7-positive lymphocytes among various lymphoid tissues in these strains was very different. In NOD mice a conspicuous population of beta 7-integrin(high) lymphocytes expressing either alpha 4, alpha E, or both, was found in nonmucosal lymphoid tissues such as peripheral lymph nodes (PLNs). They mostly expressed the PLN homing receptor L-selectin, and included both naive and memory cells on the basis of their expression of CD44/pgp-1 and CD45RB, as did the few beta 7(high) lymphocytes in BALB/c PLNs. Their homing to Peyer's patches (PPs) and PLNs was equally effective and the cells homing to PPs and PLNs were equal in their level of L-selectin and alpha 4/beta 7 expression. However, functional studies indicated that their homing to PPs mostly depended on alpha 4/beta 7-integrin, whereas they mainly used L-selectin to home to PLNs. beta 7(high) lymphocytes were found also in circulating blood of unmanipulated NOD mice, and their L-selectin expression was higher than in BALB/c mice. These results show that lymphocytes of the mucosal immune system may also express the peripheral node homing receptor L-selectin during their recirculation and that in NOD mice they frequently retain a dual homing specificity, which leads to their accumulation in nonmucosal tissues.
Animals↗
Human vascular adhesion protein 1 (VAP-1) is a unique sialoglycoprotein that mediates carbohydrate-dependent binding of lymphocytes to endothelial cells.
The regulated interactions of leukocytes with vascular endothelial cells are crucial in controlling leukocyte traffic between blood and tissues. Vascular adhesion protein-1 (VAP-1) is a novel, human endothelial cell molecule that mediates tissue-selective lymphocyte binding. Two species (90 and 170 kD) of VAP-1 exist in lymphoid tissues. Glycosidase digestions revealed that the mature 170-kD form of VAP-1 expressed on the lumenal surfaces of vessels is a heavily sialylated glycoprotein. The sialic acids are indispensable for the function of VAP-1, since the desialylated form of VAP-1 no longer mediates lymphocyte binding. We also show that L-selectin is not required for binding of activated lymphocytes to VAP-1 under conditions of shear stress. The 90-kD form of VAP-1 was only seen in an organ culture model, and may represent a monomeric or proteolytic form of the larger species. These data indicate that L-selectin negative lymphocytes can bind to tonsillar venules via the VAP- 1-mediated pathway. Moreover, our findings extend the role of carbohydrate-mediated binding in lymphocyte-endothelial cell interactions beyond the known selectins. In conclusion, VAP-1 naturally exists as a 170-kD sialoglycoprotein that uses sialic acid residues to interact with its counter-receptors on lymphocytes under nonstatic conditions.
Adult↗
Lymphocyte binding to vascular endothelium in inflamed skin revisited: a central role for vascular adhesion protein-1 (VAP-1).
The binding of leukocytes to vascular endothelium and their migration into tissues is mediated by adhesion molecules on the endothelial cells and leukocytes. Vascular adhesion protein-1 (VAP-1) is a 170-180/90-kDa endothelial molecule expressed most prominently in high endothelial venules in peripheral lymph node (PLN) type lymphatic tissues. VAP-1 mediates lymphocyte binding to PLN, tonsil and synovium. The expression of VAP-1 is induced in inflammatory diseases such as arthritis and gut inflammation. We examined the expression, structure and function of VAP-1 in normal and inflamed skin and compared it to those of other adhesion molecules implicated in skin homing. In psoriasis lichen ruber planus, pemphigoid and allergic lesions, VAP-1 was markedly upregulated. The expression of VAP-1 was also increased in biopsies of healthy skin of the patients. The VAP-1 molecule induced in skin is decorated with abundant sialic acids. VAP-1 inflamed skin is functional, since inhibition with anti-VAP-1 monoclonal antibodies caused a 60% reduction in lymphocytes adhesion to vascular endothelium. Antibodies against E-selectin, which has been regarded as the major vascular addressin directing cutaneous lymphocyte traffic, and, surprisingly, against peripheral lymph node addressin (PNAd), caused inhibitions of 30% and 60%, respectively, in the frozen section adhesion assay. These findings suggest important roles also for VAP-1 and PNAd in lymphocyte homing into inflamed skin.
Amine Oxidase (Copper-Containing)↗
Vascular adhesion protein 1 mediates binding of T cells to human hepatic endothelium.
BACKGROUND & AIMS: Molecules that regulate T-cell adhesion to hepatic endothelium and thereby recirculation of T cells to the liver are poorly understood. Because the adhesion molecule vascular adhesion protein-1 (VAP-1), which mediates lymphocyte binding to lymph node endothelium, is expressed on hepatic endothelium, it could play a role in regulating T-cell recruitment to the liver. The aim of this study was to investigate the distribution of VAP-1 expression in human liver and the ability of VAP-1 to support T-cell binding to hepatic endothelium in vitro. METHODS: Hepatic VAP-1 expression was investigated using immunohistochemistry and specific monoclonal antibodies, and VAP-1-mediated adhesion to hepatic endothelium was investigated with a tissue-binding adhesion assay using human liver sections. RESULTS: VAP-1 was expressed on sinusoidal and vascular endothelium in non-inflamed liver and in inflamed liver from patients with either allograft rejection or primary biliary cirrhosis. T cells from healthy donors bound to hepatic endothelium when added to noninflamed liver sections; this binding was inhibited by a specific anti-VAP-1 antibody but not by antibodies to intercellular adhesion molecule 1, lymphocyte function--associated antigen 1, or very late after activation (antigen) 4. VAP-1--mediated adhesion was unaffected by T-cell activation with phorbol ester. CONCLUSIONS: VAP-1 is constitutively expressed on hepatic endothelium and mediates T-cell adhesion to hepatic endothelium in vitro. VAP-1 could play a critical role in regulating T-cell recirculation to the liver in vivo.
Cell Adhesion↗
Mucosally activated circulating human B cells in diarrhea express homing receptors directing them back to the gut.
BACKGROUND & AIMS: Recirculation of mucosal lymphocytes has been established in animals but not in humans. Specific antibody-secreting cells in the blood of patients with diarrhea, initially activated in gut mucosa, are potential recirculating cells. The aim of this study was to determine whether these cells circulate back to gut by analyzing their homing receptors. METHODS: Blood mononuclear cells, separated with immunomagnetic cell sorting into receptor-positive and receptor-negative populations, were assayed for pathogen-specific antibody-secreting cells and all immunoglobulin-secreting cells using enzyme-linked immunospot assay. RESULTS: The gut mucosa homing receptor alpha4beta7 was expressed more frequently on pathogen-specific antibody-secreting cells than on immunoglobulin-secreting cells of healthy controls (P<0.001). Conversely, L-selectin, a homing receptor for peripheral lymph nodes, was found on remarkably fewer antibody-secreting cells of the patients compared with immunoglobulin-secreting cells of controls (32.9% and 70.3%, respectively; P<0.001). Three to 6 months after the disease, specific antibody-secreting cells had disappeared and frequency of L-selectin-and alpha4beta7-expressing cells had returned to control levels. CONCLUSIONS: Circulating mucosally activated antibody-secreting cells express a set of homing receptors guiding them back to the gut. This provides evidence for recirculation of mucosal lymphocytes in humans.
Adult↗
Mucosa-associated (beta 7-integrinhigh) lymphocytes accumulate early in the pancreas of NOD mice and show aberrant recirculation behavior.
The mucosal addressin cell adhesion molecule-1 (MAdCAM-1) becomes expressed on islet vessels of NOD mice early during lymphocyte accumulation in islets. Because MAdCAM-1 preferentially mediates the homing of mucosal lymphocytes, islet-associated MAdCAM-1 could favor the accumulation of mucosal lymphocytes in pancreatic islets. Therefore, we investigated the relative frequency of islet-infiltrating lymphocytes with a mucosal phenotype (alpha 4/beta 7-integrinhigh and L-selectinlow) at early and advanced stages of insulitis. We found that until the age of 12 weeks, lymphocytes with a mucosal phenotype were particularly frequent in the pancreas (percentage of beta 7-integrinhigh-lymphocytes was 48% at 8 weeks and 73% at 12 weeks), whereas in diabetic mice older than 16 weeks, their relative number was smaller (26% of pancreas-infiltrating lymphocytes). To define the origin and homing behavior of beta 7-integrinhigh-lymphocytes before their accumulation in pancreatic islets in NOD mice, we sought for such lymphocytes in different lymphoid organs and studied their recirculation. We found that compared with lymphocytes in several other strains, in NOD mice such lymphocytes were most frequent in nonmucosal lymphoid tissues (peripheral and pancreatic lymph nodes, spleen) from an early age. When injected to blood circulation, mucosal beta 7high-lymphocytes failed to home efficiently back to mucosal lymphoid tissue in NOD mice but homed aberrantly to nonmucosal lymphoid tissues. After adoptive transfer of diabetogenic splenocytes, the first lymphocytes accumulating in the pancreas were predominantly beta 7-integrinhigh. We conclude that mucosa-associated lymphocytes are involved in the early phases of islet-inflammation in NOD mice and that the aberrant homing behavior of lymphocytes expressing high levels of beta 7-integrin may associate with their accumulation in pancreatic islets early during insulitis.
Aging↗
CD73 is involved in lymphocyte binding to the endothelium: characterization of lymphocyte-vascular adhesion protein 2 identifies it as CD73.
We have recently described a monoclonal antibody (mAb) 4G4 recognizing a 70-kD molecule constitutively expressed on human endothelial cells and on subpopulations of lymphocytes. We showed that this molecule, which we named lymphocyte-vascular adhesion protein 2 (L-VAP-2), mediates lymphocyte adhesion to cultured endothelial cells. Protein sequencing of tryptic peptides from immunoaffinity-purified L-VAP-2 revealed sequence identity between L-VAP-2 and CD73 (ecto-5'-nucleotidase, E.C.3.1.3.5), and COS cells transfected with a CD73 cDNA were positively stained with the mAb 4G4, which recognizes L-VAP-2. mAb 4G4 was also able to partially inhibit the ecto-5'-nucleotidase activity of peripheral blood lymphocytes. Moreover, cross-precipitation studies performed with mAb 4G4 and a CD73 workshop mAb 1E9 showed that these two antibodies recognize the same molecule. Since the tissue distribution and biochemical characteristics of the two molecules are also similar, we conclude that L-VAP-2 and CD73 are the same glycoprotein. Adhesion experiments showed significantly increased binding of freshly isolated lymphocytes to COS cells transfected with a CD73 cDNA, as compared to mock-transfected COS cells, and binding of lymphocytes to CD73-expressing COS cells was inhibited by the presence of mAb 4G4 in the adhesion assay. CD73 is a glycosyl phosphatidylinositol-linked molecule previously shown to have a cosignalling role in T lymphocyte proliferation. Our data suggest that it also has a function in mediating lymphocyte adhesion to the endothelium.
5'-Nucleotidase↗
Tumor endothelium selectively supports binding of IL-2-propagated tumor-infiltrating lymphocytes.
Entrance of activated T cells into the tumor after adoptive transfer is a prerequisite for the efficacy of this form of immunotherapy. Because lymphocyte binding to vascular endothelium is the critical step in which lymphocyte extravasation into the tissue is controlled, we compared adhesion of tumor-infiltrating lymphocytes (TIL) to endothelial cells in tumors, peripheral lymph nodes, mucosa-associated lymphatic tissues, and inflamed synovium. Simultaneously, expression of the known homing-associated Ags both on TIL and tumor vasculature was analyzed. All TIL strongly expressed alpha 4-integrins, LFA-1 and CD44, whereas only a low level of L-selectin expression was detected. Tumor vasculature showed signs of activation in each patient on the basis of elevated levels of intercellular adhesion molecule-1, E-selectin, vascular cell adhesion molecule-1, and/or peripheral lymph node addressin (PNAd). TIL showed significantly enhanced binding to tumor vasculature in comparison with other endothelial specificities. Increased binding was not markedly due to up-regulation of the inflammation-induced endothelial cell adhesion molecules in tumors, because binding to inflamed synovium that expressed the same adhesion molecules was not enhanced. In summary, TIL show preferential binding to tumor vasculature and the binding is partially mediated by currently unknown mechanisms. In vitro analysis of endothelial cell binding properties may help to identify those TIL populations that will have the best potential to home back to tumor tissue after adoptive transfer.
Adult↗
Dual binding capacity of mucosal immunoblasts to mucosal and synovial endothelium in humans: dissection of the molecular mechanisms.
Lymphocytes continuously migrate throughout the body in search of antigens. Virgin lymphocytes recirculate freely between the blood and different lymphatic organs, whereas immunoblasts extravasate preferentially into sites similar to those where they initially responded to antigen. Tissue-specific extravasation of lymphocytes is largely controlled by distinct lymphocyte surface receptors that mediate lymphocyte binding to high endothelial venules (HEV). In the present study, the molecular mechanisms determining the specificity of human mucosal (lamina propria) lymphocyte binding to different endothelial recognition systems were analyzed. Mucosal immunoblasts adhered five times better than small mucosal lymphocytes to mucosal HEV. Importantly, mucosal immunoblasts also bound to synovial HEV almost as efficiently as to mucosal HEV, but they did not adhere to peripheral lymph node HEV. To study the impact of different homing-associated molecules in this dual endothelial binding, we used a gut-derived T cell line and freshly isolated mucosal immunoblasts. Both cell types expressed integrins alpha 4, beta 1, beta 7, and lymphocyte function associated antigen 1 (LFA-1), and were CD44 positive, but practically L-selectin negative. Binding of mucosal immunoblasts to mucosal HEV was almost completely abolished by pretreatment with anti-beta 7 monoclonal antibodies, but it was independent of alpha 4/beta 1 function. In contrast, alpha 4/beta 1 partially mediated immunoblast adherence to synovial HEV, whereas alpha 4/beta 7 had only a minor role in adherence of blasts at this site. CD44 and LFA-1 contributed to HEV-binding both in mucosa and synovium. Taken together, this is the first report that demonstrates a critical role for alpha 4/beta 7 in the binding of gut lymphocytes to mucosal venules in humans. Moreover, a hitherto unknown interaction between mucosal effector cells and synovial endothelial cells was shown to be only partially mediated by the currently known homing receptors. The dual endothelial binding capacity of mucosal blasts may help to explain the pathogenesis of reactive arthritis not uncommonly associated with inflammatory and infectious bowel disease.
Carrier Proteins↗
Different forms of human vascular adhesion protein-1 (VAP-1) in blood vessels in vivo and in cultured endothelial cells: implications for lymphocyte-endothelial cell adhesion models.
Vascular endothelium plays a pivotal role in controlling leukocyte extravasation from the blood into the tissues. Vascular adhesion protein-1 (VAP-1) is a novel endothelial cell molecule which mediates lymphocyte binding to the vascular lining (Salmi, M., and Jalkanen, S., Science 1992. 257:1407). In this study, we analyzed endothelial cell type-specific differences of VAP-1. In vivo, VAP-1 is a 90/170-kDa molecule which is mainly expressed on the lumenal surface and in cytoplasmic granules of peripheral lymph node-type postcapillary venules (high endothelial venules, HEV). In tonsil HEV, VAP-1 is modified with abundant sialic acids. VAP-1 is also detectable in the cytoplasm of human umbilical vein endothelial cells (HUVEC) and in an endothelial cell hybrid EaHy-926, although both cell types lack detectable surface VAP-1. Cultured endothelial cells do not express MECA-79-defined peripheral lymph node addressins either. VAP-1 was not translocated onto the endothelial cell surface after stimulation with multiple cytokines, mitogens or secretagogues which induced expression of other known endothelial adhesion molecules. Biochemical analyses revealed that VAP-1 is a approximately 180-kDa protein in these endothelial cell types. Digestions with neuraminidase, O-glycanase and N-glycanase, as well as treatment of cells with tunicamycin and benzyl-N-acetylgalactosaminide, did not alter the molecular mass of VAP-1 in EaHy-926. Pulse-chase experiments showed that VAP-1 is directly synthesized as a 180-kDa molecule without any detectable precursors. Thus, in cultured endothelial cells, VAP-1 is a 180-kDa protein which is devoid of post-translational modifications, and in particular, lacks the sialic acids crucial for the function of VAP-1 in tonsil vessels. Notably, the endothelial cell types commonly used as a model in studying lymphocyte-endothelial cell interactions lack surface expression of VAP-1 and peripheral node addressins, and hence are inherently of limited use in analyses of the initial adhesion of lymphocytes.
Acetylgalactosamine↗
Serum CD44 in malignant lymphoma: an association with treatment response.
CD44, a cell surface glycoprotein, is involved in lymphocyte trafficking from the blood to lymphatic tissues, and is of importance in dissemination of lymphoma. A variant form of CD44 that has additional amino acids in the common protein backbone (CD44v6) also seems to play a role in the metastatic dissemination of malignancies. We measured serum CD44 and CD44v6 in 34 patients with lymphoma and in healthy controls by dot blot assay. Small amounts of both CD44 (range, 10 to 80 ng/mL) and CD44v6 could be detected in sera of all controls. Serum CD44 was elevated in all patients with lymphoma before treatment (range, 70 to > 2,000 ng/mL, P < .0001), and CD44v6 was also slightly elevated. Serum CD44 levels correlated with response to treatment. Patients with complete response achieved similar CD44 levels as the controls, whereas those with progressive disease had increased serum CD44 levels. We conclude that both the standard and the variant form of CD44 are detectable in sera of healthy individuals, and that serum CD44 may be useful in monitoring treatment response in patients with lymphoma.
Adolescent↗
Aberrant binding of lamina propria lymphocytes to vascular endothelium in inflammatory bowel diseases.
BACKGROUND/AIMS: Lymphocyte recirculation between the blood and lymphoid tissues as well as lymphocyte migration into inflammatory sites are controlled by lymphocyte interaction with vascular endothelium. The aim of this study was to compare the endothelial binding mechanisms of lamina propria lymphocytes (LPL) isolated from normal and inflamed bowel. METHODS: Binding of LPL from normal and inflamed (inflammatory bowel disease) bowel to endothelium was studied using an in vitro binding assay. Expression of adhesion molecules on LPL and on mucosal endothelial cells was analyzed by flow cytometry and immunohistochemistry. RESULTS: In inflammatory bowel disease, the selectivity of lymphocyte-endothelial interaction was lost, i.e., immunoblasts bound well not only to mucosal vessels but also to peripheral lymph node venules. The set of homing receptors expressed on mucosal immunoblasts did not directly predict the endothelial binding properties of these cells; e.g., L-selectin-negative blasts adhered well to lymph node vessels using peripheral lymph node-specific endothelial adhesion antigen (PNAd). PNAd was aberrantly expressed in vessels in the inflamed mucosa, where it also mediated LPL binding. CONCLUSIONS: These findings are important in understanding the physiology of lymphocyte homing into the gut and suggest an important role for PNAd in the pathogenesis of inflammatory bowel disease.
Antigens, Surface↗
Induction and function of vascular adhesion protein-1 at sites of inflammation.
Emigration of leukocytes from the blood into the tissues is critical in controlling lymphocyte patrolling in different lymphatic organs and in leukocyte accumulation at sites of inflammation. During the first stage of the extravasation process, leukocytes bind to the endothelial lining of vessels. At the molecular level, several adhesion molecules on leukocytes and endothelial cells function as receptor-ligand pairs in mediating this dynamic interaction. Recently, we have identified a novel human endothelial cell molecule, vascular adhesion protein 1 (VAP-1), that mediates lymphocyte binding (Salmi, M., and S. Jalkanen. 1992. Science [Wash. DC] 257:1407). VAP-1 was initially characterized by mAb 1B2 which inhibits lymphocyte adhesion to high endothelial venules (HEV) and to purified VAP-1 protein. Here we report the location and function of VAP-1 in normal and inflamed tissues in humans. VAP-1 is abundant in HEV of lymphatic organs belonging to the peripheral lymph node system, but considerably less is expressed in vessels of mucosa-associated lymphatic tissues. A subset of venules in most normal nonlymphatic tissues like skin, brain, kidney, liver, and heart is also VAP-1 positive. In addition to vessels, VAP-1 is distributed on a few other cell types, most notably in dendritic-like cells of germinal centers. At sites of inflammation, such as in inflammatory bowel diseases and chronic dermatoses, expression of VAP-1 is clearly increased. The induced VAP-1 is functional, since mAb 1B2 inhibits lymphocyte binding to inflamed lamina propria venules by approximately 60%. Thus VAP-1 is an endothelial adhesion molecule that under normal conditions is expressed mainly in HEV of lymphatic tissues. However, expression of functional VAP-1 in vivo is upregulated during an inflammatory reaction at other sites as well. Inducibility of VAP-1 suggests that it may play a significant role, not only in recirculation of lymphocytes, but also in controlling entry of leukocytes into sites of inflammation.
Amine Oxidase (Copper-Containing)↗
Lymphocyte-vascular adhesion protein-2 is a novel 70-kDa molecule involved in lymphocyte adhesion to vascular endothelium.
Extravasation of leukocytes from the blood is essential for normal lymphocyte recirculation as well as in mounting an adequate inflammatory response in different tissues. Leukocyte migration from the blood is controlled by sophisticated interactions between surface receptors on leukocytes and their corresponding endothelial cell ligands. Here we describe a novel adhesion molecule, lymphocyte-vascular adhesion protein-2 (L-VAP-2), recognized by 4G4 mAb that was produced by immunizing mice with an enriched endothelial cell preparation isolated from inflamed human synovium. mAb 4G4 stains a subpopulation of venules in lymphoid and nonlymphoid tissues as well as a few high endothelial venules in lymphoid tissues. L-VAP-2 is constitutively expressed on human umbilical vein endothelial cells, and its expression cannot be up-regulated by cytokines and mitogens such as TNF-alpha, IL-1, and LPS. The Ag is expressed on approximately 20% of PBL, whereas granulocytes and monocytes are negative. On lymphocytes, L-VAP-2 is preferentially expressed on B cells and CD8+ T cells. The molecular mass of L-VAP-2 is approximately 70 kDa as determined from immunoprecipitated, 125I-labeled endothelial cell lysates. The involvement of L-VAP-2 in lymphocyte binding to endothelium was tested in vitro using human umbilical vein endothelial cells. Both the intact antibody and F(ab')2 fragments of it consistently inhibited lymphocyte binding to human umbilical vein endothelial cells by approximately 25%. On the basis of the molecular mass estimation and the staining of tissue sections, leukocyte populations, and ICAM-1 and ICAM-2 transfectants, L-VAP-2 appears to be a novel Ag involved in the lymphocyte-endothelial cell interaction.
Animals↗
Regulated expression of exon v6 containing isoforms of CD44 in man: downregulation during malignant transformation of tumors of squamocellular origin.
CD44 is a family of glycoproteins involved in cell-cell and cell-matrix interactions. In addition to the major 90-kD form present on most hematopoietic cells, larger 140-230 kD forms are found on keratinocytes and carcinoma cell lines. These bigger isoforms of CD44 arise by alternative splicing that results in insertion of one or more of the "variant" exons into the extracellular part of the 90-kD constant form of the molecule. In rat, v6 (variant exon v6) containing form of CD44 confers metastatic potential to carcinoma cells, and therefore, it is of interest to study the distribution of this isoform in humans. We raised antibodies against a synthetic peptide containing a sequence encoded by the exon v6. A mAb thus obtained (designated Var3.1) strongly reacted with the plasma membranes of squamous cells in upper layers of skin and tonsil surface epithelia. Weaker staining was seen in germinal centers, vascular endothelia and enterocytes. Exon v6 containing forms of CD44 (CD44v6) were absent from tissue leukocytes and connective tissue components. In comparison, Hermes-3 epitope (on the constant part) containing forms of CD44 were preferentially localized in basal layers of epithelia, present on the surface on most leukocytes and connective tissue cells, and undetectable on the luminal surface of high endothelial venules. In benign neoplasms, epithelial cells stained with mAb Var3.1 like in normal tissues. In contrast, immunostaining of 30 squamous carcinoma specimens (both primary and metastatic lesions) revealed that malignant transformation resulted in downregulation or disappearance of Var3.1 epitope, but in majority of cases, not in diminished synthesis of the Hermes-3 epitope. Biochemical analyses showed that mAb Var3.1 recognized two major forms of CD44 (220 and 300 kD). In conclusion, epitopes on exon v6 and constant part of CD44 are differentially synthesized and regulated during normal and malignant growth of cells in man.
Adult↗