Lymphocyte migration to inflamed lacrimal glands is mediated by vascular cell adhesion molecule-1/alpha(4)beta(1) integrin, peripheral node addressin/l-selectin, and lymphocyte function-associated antigen-1 adhesion pathways

Sjogren's syndrome is an autoimmune disease characterized by inflammation and destruction of lacrimal and salivary glands. The development of the inflammation requires the migration of lymphocytes from the blood into these tissues. This migration involves multistep cascades with binding of lacrimal gland endothelial adhesion molecules to their ligands on circulating lymphocytes. We used nonobese diabetic mice, which develop autoimmune-mediated lacrimal gland inflammation, as an experimental model to define the adhesion molecules that control lymphocyte migration into inflamed lacrimal glands. We found that vascular endothelia in inflamed areas of lacrimal gland expressed vascular cell adhesion molecule (VCAM)-1 and the peripheral node addressin (PNAd), but not mucosal addressin cell adhesion molecule-1. Most lymphocytes in the inflamed glands expressed alpha(4) integrin, L-selectin, and lymphocyte function-associated antigen (LFA)-1. In vivo studies revealed that antibodies against VCAM-1, alpha(4) integrin, PNAd, L-selectin, or LFA-1 almost completely blocked lymphocyte migration from blood into inflamed lacrimal glands. There was no inhibition of migration by antibodies against mucosal addressin cell adhesion molecule-1 or alpha(4)beta(7) integrin. These results indicate that endothelial/lymphocyte adhesion cascades involving VCAM-1/alpha(4)beta(1) integrin, PNAd/L-selectin, and LFA-1 control the migration of lymphocytes into inflamed lacrimal gland. These adhesion molecules offer potential therapeutic targets to block the development of lacrimal gland inflammation and destruction.

Multiple defects in Fc epsilon RI signaling in Syk-deficient nonreleaser basophils and IL-3-induced recovery of Syk expression and secretion

Human basophils respond to Ag-induced cross-linking of their high affinity IgE receptor, FcepsilonRI, by releasing histamine and other mediators from granules, producing IL-4 and other cytokines and, as shown in this study, by forming membrane ruffles and showing increased very late Ag-4 (VLA-4)-mediated adhesion to VCAM-1-expressing target cells. We have identified five blood donors whose basophils lack detectable levels of the FcepsilonRI-associated protein tyrosine kinase, Syk. Despite showing no obvious ultrastructural differences from normal basophils, nonreleaser basophils fail to form membrane ruffles, to show increased VLA-4-mediated adhesive activity, or to produce IL-4 in response to FcepsilonRI cross-linking. Although Syk protein levels are suppressed in basophils from all five donors, Syk mRNA is consistently present. Furthermore, culturing nonreleaser basophils for 4 days with IL-3 restores Syk protein expression and FcepsilonRI-mediated histamine release. Understanding the reversible suppression of Syk protein expression in nonreleaser basophils, and learning to replicate this property in patients with allergic inflammation could be a powerful and specific way to limit symptomatic disease.

A small-molecule, tight-binding inhibitor of the integrin alpha(4)beta(1) blocks antigen-induced airway responses and inflammation in experimental asthma in sheep

The leukocyte integrin very late antigen-4 (alpha(4)beta(1), CD49d/CD29) is an adhesion receptor that plays an important role in allergic inflammation and contributes to antigen-induced late responses (LAR) and airway hyperresponsiveness (AHR). In this study, we show that single doses of a new small-molecule, tight-binding inhibitor of alpha(4), BIO-1211, whether given by aerosol or intravenously, either before or 1.5 h after antigen challenge blocks allergen- induced LAR and post-antigen-induced AHR in allergic sheep. Multiple treatments with doses of BIO-1211 that were ineffective when given singly, were protective. BIO-1211 also provided dose-dependent inhibition of the early airway response (EAR) to antigen. In conjunction with the functional protection against the antigen-induced LAR and AHR, sheep treated with BIO-1211 before challenge showed significantly reduced: (1) numbers of eosinophils in bronchoalveolar lavage (BAL), (2) BAL levels of the inflammatory marker tissue kallikrein, and (3) numbers of inflammatory cells (lymphocytes, eosinophils, metachromatic staining cells, and neutrophils) in bronchial biopsies obtained after challenge when compared with corresponding biopsies after vehicle treatment. More importantly, we show for the first time that an inhibitor of alpha(4) was able to reverse post-antigen-induced AHR, thereby decreasing the time of recovery from the normal period of > 9 d to 3 d. Our results show that effective inhibition of antigen-induced airway responses can be achieved with single doses of a potent small-molecule inhibitor of alpha(4) and that such agents may be used therapeutically, as well as prophylactically, to alleviate allergen- induced inflammatory events. These data provide further support and extend the evidence for the role of alpha(4) integrins in the pathophysiologic events that follow airway antigen challenge.

Modulation of integrin function in hematopoietic progenitor cells by CD43 engagement: possible involvement of protein tyrosine kinase and phospholipase C-gamma

Attachment of cells to extracellular matrix components is critical for the regulation of hematopoiesis. CD43 is a mucin-like transmembrane sialoglycoprotein expressed on the surface of almost all hematopoietic cells. A highly extended structure of extracellular mucin with negative charge may function as a repulsive barrier to hematopoietic cells. However, some investigators have shown that CD43 has proadhesive properties, and engagement of CD43 has been reported to upregulate integrin-mediated cell adhesion in T cells. We found that cross-linking of CD43 with monoclonal antibodies (MoAbs) enhanced integrin alpha4beta1 (very late antigen [VLA]-4) and alpha5 beta1 (VLA-5)-dependent adhesion of human cord blood CD34(+) cells to fibronectin. CD34(+) CD38(hi), but not CD34(+)CD38(-/low) cells responded significantly to the stimulus, suggesting that committed, but not stem and more immature progenitors are sensitive to CD43-mediated activation of integrin. To elucidate the molecular mechanism leading to integrin activation, we used the growth factor-dependent cell line MO7e. Cross-linking of CD43 induced tyrosine phosphorylation of several intracellular molecules including the protein tyrosine kinase Syk, the proto-oncogene product Cbl, and phospholipase C (PLC)-gamma2 in MO7e cells. Moreover, protein tyrosine kinase inhibitor herbimycin A and PLC inhibitor U73122 both blocked CD43-induced enhancement of adhesion to fibronectin. These results indicate that signals mediated through CD43 may increase integrin affinity to fibronectin via a pathway dependent on protein tyrosine kinase and PLC-gamma activation in hematopoietic progenitors.

Role of very late adhesion integrins in mediating repair of human airway epithelial cell monolayers after mechanical injury

Repair of the airway epithelium after injury requires that processes such as adhesion and cell migration occur in a defined order. Both of these processes depend on interactions between extracellular matrix (ECM) proteins and appropriate integrins. To study these interactions, we examined monolayer wound repair in a cultured human airway epithelial cell line, 16HBE14o-. Wounds created in confluent monolayers grown on either collagen-IV, laminin-1, or laminin-2 matrix closed quickly in response to 15 ng/ml epidermal growth factor (EGF). Concurrent treatment of cells grown on each matrix protein with EGF and a monoclonal antibody (mAb) to beta1-integrin inhibited wound closure. Treatment with a mAb to alpha2-, alpha3-, and alpha6-integrin blocked wound repair in monolayers grown on collagen-IV but did not do so in monolayers grown either on laminin-1 or laminin-2. Inhibition was not due to cell detachment or apoptosis. These data demonstrate that integrins expressed by airway epithelial cells mediate wound closure on different constitutive ECM proteins. These data suggest that beta1-integrin subunit function is required to permit migration and spreading of epithelial cells, and that alpha-integrin subunits alone do not mediate migration of epithelial cells grown on either laminin-1 or laminin-2. These differences may become important if the matrix protein composition of airway basement membrane changes in disease states such as asthma.

High affinity very late antigen-4 subsets expressed on T cells are mandatory for spontaneous adhesion strengthening but not for rolling on VCAM-1 in shear flow

The very late Ag-4 (VLA-4) integrin supports both rolling and firm adhesion of leukocytes on VCAM-1 under shear flow. The molecular basis for the unique ability of a single adhesion molecule to mediate these versatile adhesive processes was investigated. VLA-4 occurs in multiple activation states, with different affinities to ligand. In this study we tested how these states regulate VLA-4 adhesiveness under shear flow in Jurkat T cells and PBL. VLA-4 on nonstimulated Jurkat cells supported rolling and spontaneous arrest on VCAM-1, whereas a Jurkat activation mutant with reduced VLA-4 affinity failed to spontaneously arrest after tethering to or during rolling on VCAM-1. The contribution of VLA-4 affinity for ligand to rolling and spontaneous arrests on immobilized VCAM-1 was dissected using soluble VLA-4 ligands, which selectively block high affinity states. VLA-4 saturation with ligand completely blocked spontaneous adhesion strengthening post-tethering to VCAM-1, but did not impair rolling on the endothelial ligand. High affinity VLA-4 was found to comprise a small subset of VLA-4 on resting Jurkat cells and PBL. This subset is essential for firm adhesion but not for tethering or rolling adhesions on VCAM-1. Interestingly, low and high affinity VLA-4 states were found to mediate similar initial tethering to ligand. High affinity VLA-4, constitutively expressed on circulating T cells, may control their early adhesion strengthening on VCAM-1-expressing endothelium before exposure to vascular chemokines and activation of additional integrins.

Cross-species interaction of porcine and human integrins with their respective ligands: implications for xenogeneic tolerance induction

BACKGROUND

Organ transplantation is limited by the number of available donors. One possible solution would be the use of pigs as organ donors. However, current immunosuppressive protocols cannot prevent rejection of these organs. If donor-specific tolerance toward porcine antigens could be induced in recipients, subsequent implantation of porcine organs would be possible without further immunosuppression. Induction of tolerance can be achieved with a bone marrow transplant if donor antigen-presenting cells successfully differentiate in the recipient thymus to induce deletion of donor-reactive host cells. Migration of porcine progenitor cells to the host marrow and thymus and differentiation into tolerance-inducing antigen-presenting cells is likely to require successful interaction of porcine adhesion molecules with human ligands. In this study, we investigated whether very late antigen (VLA)4 and VLA-6 integrins, which play important roles in homing and differentiation of hematopoietic progenitor cells, function across the pig-to-human species barrier.

METHODS

Static cell-to-cell and cell-to-extracellular matrix protein adhesion assays were used to examine the cross-species interaction of porcine adhesion molecules with human ligands.

RESULTS

Our studies show that porcine cells adhere to various human endothelial cell monolayers and extracellular matrix proteins and demonstrate that porcine VLA-4 and VLA-6 appear to be fully cross-reactive to the human ligands vascular cell adhesion molecule-1 and laminin, respectively.

CONCLUSIONS

It is likely that porcine hematopoietic progenitor cells will be able to successfully employ pVLA-4- and pVLA-6-human ligand interactions in a pig-to-human bone marrow transplantation model in order to induce donor-specific tolerance.

A role for the VLA-4 integrin in the activation of human memory B cells

It is generally recognized that activation through membrane effector molecules such as CD40 or the B cell receptor (BCR) is mandatory to allow B cells to proliferate and differentiate into antibody (Ab)-secreting cells in response to cytokines. We show here that purified tonsillar B cells can be stimulated directly by a cytokine combination to proliferate and secrete immunoglobulins when cultures are performed at high cell density. The contact-mediated activation of B cells in this experimental system is strongly inhibited both by anti-very late antigen (VLA)-4 monoclonal Ab and by a peptide containing the LDV sequence specifically recognized by the alpha 4 integrin binding site. These reagents also significantly suppressed the B cell responses elicited by engagement of the BCR or CD40. Our data reveal that memory B cells but not virgin or germinal center B cells are sensitive to the direct stimulatory effect of cytokines in high-density cultures. Finally, we found that the dual expression of the alpha and beta chains of VLA-4 is a distinctive feature of the memory B cell population. Collectively, our findings support the notion that VLA-4-dependent homotypic B cell interactions can mediate a co-stimulatory signal to human memory B cells and might participate in the B cell activation triggered through the BCR and CD40.

Mesenchymal cells stimulate human intestinal intraepithelial lymphocytes

BACKGROUND & AIMS

Intraepithelial lymphocytes (IELs) from human intestinal mucosa proliferate minimally to T-cell stimuli. Optimal growth may depend on factors that are missing in vitro, such as accessory cells. The aim of this study was to determine whether mesenchymal cells costimulate IELs.

METHODS

IELs were isolated from human jejunum and cultured with fibroblasts or smooth muscle cells (mesenchymal cell models for mucosal myofibroblasts) and various T-cell stimuli. Proliferation was determined by [3H]thymidine incorporation, and interleukin 2 (IL-2) production was measured by enzyme-linked immunosorbent assay. Surface molecules were detected by immunofluorescence and flow cytometry.

RESULTS

The proliferative responses of IELs to mitogen (phytohemagglutinin), superantigen (staphylococcal enterotoxin B), or anti-CD3 antibody were increased greatly by coculture with mesenchymal cells, while only slightly by peripheral-blood monocytes, the classical antigen-presenting cells. IL-2 production and receptor expression also increased. Mesenchymal cell costimulation of IEL growth required direct contact between the two cell types and was partly dependent on the integrin alpha4beta1 (very late activation 4[VLA-4]) and major histocompatibility complex (MHC) class I, as their respective antibodies blocked the effect. The surface molecules B7 (CD80), CD2, and MHC class II were not involved.

CONCLUSIONS

Optimal IEL growth depends on their contact with mesenchymal cells, an interaction that is mediated by VLA-4 and MHC class I. In mucosal immunity, basement membrane myofibroblasts likely serve this role.

Granulocyte-macrophage colony-stimulating factor regulates the functional adhesive state of very late antigen-4 expressed by eosinophils

As very late antigen-4 (VLA-4) can exist in different functional states, we have sought to determine whether a cytokine expressed by inflamed endothelium (i.e., granulocyte-macrophage CSF (GM-CSF)) could regulate the functional state of VLA-4 expressed by eosinophils. Using a micropipette single cell adhesion assay able to measure the strength of adhesion forces, eosinophils exhibited low levels of basal adhesion to unstimulated endothelium (separation force, 0.022 +/- 0.003 mdynes). In contrast, individual eosinophils bound to IL-1beta-stimulated endothelium (0.49 +/- 0.02 mdynes), TNF-stimulated endothelium (0.62 +/- 0.05 mdynes), or IL-4-stimulated endothelium (0.11 +/- 0.01 mdynes) with increased avidity as assessed by separation force. Eosinophil binding to IL-4-stimulated endothelium was significantly inhibited by neutralizing Abs to either vascular cell adhesion molecule (VCAM) or VLA-4. The strength of eosinophil adhesion to VCAM (0.31 +/- 0.02 mdynes) or to connecting segment-1 (CS-1) (0.18 mdynes) was greater than the strength of eosinophil adhesion to unstimulated endothelium (0.02 mdynes), but was less than the strength of eosinophil adhesion to IL-1beta-stimulated endothelium (0.49 +/- 0.02 mdynes). After incubating eosinophils for 30 min with GM-CSF, the mean adhesion strength of eosinophils to CS-1 and VCAM increased significantly by 84 and 54%, respectively, compared with that of controls. This increased binding of eosinophils to VCAM or CS-1 was not due to alterations in VLA-4 receptor number (assessed by FACS analysis) or alterations in VLA-4 receptor distribution (assessed by confocal microscopy). These studies suggest that endothelial-derived cytokines such as GM-CSF have the potential to alter the functional state of eosinophil-expressed VLA-4 from a low affinity state to a high affinity state.

Immunoregulatory roles of adhesive interactions between lymphocytes and gingival fibroblasts

Chronic adult periodontitis is usually characterized by inflammatory cell accumulation in the extravascular periodontal connective tissue. In order to reveal how the lymphocyte migration and retention in periodontal lesions is regulated, we have focused on the molecular basis for the adhesive interactions between lymphocytes and human gingival fibroblasts (HGF). In this study, we investigated the involvement of cell adhesion molecules in adhesive interactions between lymphocytes and HGF. We found that activated lymphocytes bound strongly to HGF and VLA integrins, extracellular matrix receptors, play crucial roles in the binding. Interestingly, we first revealed that CD44 molecules (hyaluronate receptor) on lymphocytes also participated in lymphocyte-HGF interactions and that hyaluronate anchored on the surface of HGF functioned as the ligand for CD44. In addition, when HGF were stimulated with inflammatory cytokines such as IL-1, TNF alpha and IFN gamma, the binding avidity between lymphocytes and HGF was significantly increased and the adhesion was mainly mediated by LFA-1/ICAM-1 pathway. We then examined the possibility whether lymphocyte-HGF interaction may cause activation of HGF. When HGF directly interacted with lymphocytes for 3 h, IL-1 beta mRNA expression was clearly increased in HGF. These findings suggested that the adhesive interactions between lymphocytes and HGF was mediated at least by VLA integrins, LFA-1/ICAM-1 and CD44/hyaluronate and that the heterotypic cell-cell interactions could mutually cause intracellular signal transduction.

Correlation of very late activation integrin and CD44 expression with extrarenal invasion and metastasis of renal cell carcinomas

Cell adhesion molecules mediate cell-cell and cell-matrix interactions, and they are thought to play an important role in tumor invasion and metastasis. Altered expression of integrins and CD44 in renal cell carcinoma has been recently demonstrated, but an association with invasive or metastatic behavior has not been reported. We examined very late activation (VLA) integrin and CD44 expression in 37 renal cell carcinomas and correlated adhesion molecule expression with multiple histological and clinical parameters. Most tumors exhibited positive staining for VLA3 (81%). Approximately one third of the tumors stained positively for VLA6 and CD44, and fewer (27%) were positive for VLA2. Only a few tumors were positive for VLA4 (8%) and VLA5 (14%). Most of the tumors exhibiting positive staining showed a combination of membranous and cytoplasmic staining patterns. Low-grade tumors positive for VLA6 showed a tendency for basilar staining of the tumor cells, whereas high-grade tumors exhibited diffuse cytoplasmic staining. All tumors exhibiting weak or strong positive staining for VLA4 or VLA5 showed extrarenal invasion or were known to have developed metastases at the time of nephrectomy. All tumors strongly positive for VLA2 or CD44 showed invasion beyond the renal capsule or metastases. In contrast to a previous study, no association was observed between positive staining and tumor grade. Nor were tumor size, architectural pattern, cell type, or DNA ploidy found to be associated with particular staining patterns. Although many of the invasive tumors showed no difference in VLA integrin or CD44 expression compared with tumors confined to the kidney, increased expression in some of them suggests that these cell adhesion molecules may contribute to the invasive or metastatic phenotype.

Role of VLA-integrin receptor in invasion and metastasis of human fibrosarcoma cells

Anti-invasive and anti-metastatic effects of anti-integrin antibodies (against VLA-alpha 2, alpha 4, beta 1) were examined on human fibrosarcoma cells using in vitro invasion assay in a reconstituted basement membrane (Matrigel) and experimental metastatic assay in a chick embryo. The effects of anti-integrin antibodies were compared with those of RGD-containing peptides (GRGDS), which have been known as effective inhibitors of tumor cell metastasis. Although slight differences in effective concentration among antibodies were observed, invasion and metastasis were significantly inhibited by anti-integrin antibodies. The results also showed partial inhibitory effect of GRGDS on the invasion and metastasis of human fibrosarcoma cells. These results indicate that integrin receptors mediating cell-cell/cell-extracellular matrix components interactions play a key role in the invasion and metastasis of human fibrosarcoma cells.

Selective homing of human leukemic B-cell precursors to specific lymphohematopoietic microenvironments in SCID mice: a role for the beta 1 integrin family surface adhesion molecules VLA-4 and VLA-5

We used a SCID mouse xenograft model to study the in vivo growth patterns of primary leukemic cells from six patients with newly diagnosed B-cell precursor (BCP) acute lymphoblastic leukemia (ALL), including two patients with t(1;19) ALL, two patients with t(4;11) ALL, and two patients with t(9;22) ALL. Leukemic cells from these six patients caused overt leukemia in SCID mice with extensive multiple organ involvement. Leukemic BCP from SCID mice xenografted with leukemic cells from two t(9;22) ALL patients expressed very high levels of both VLA-4 and VLA-5 regardless of the tissue of origin. By comparison, in SCID mice xenografted with leukemic cells from the two patients with t(1;19) ALL and two patients with t(4;11) ALL, leukemic BCP from the bone marrow samples expressed high levels of VLA-4 as well as VLA-5, whereas the vast majority of leukemic BCP in the liver or spleen samples expressed neither of these adhesion molecules at significant levels. These results suggest that the expression of VLA-4 and VLA-5 on t(1;19) or t(4;11) leukemia cells likely determines their binding capacity to bone marrow stroma and may affect their migration to extramedullary tissues. Our findings are in accord with and extend previous studies which demonstrated that extracellular matrix and integrins influence development, compartmentalization, and migration of BCP during B-cell ontogeny. The described SCID mouse model system provides a unique opportunity to study the adhesion receptors which regulate the selective homing of human leukemic BCP to specific SCID mouse organs.

Signal transduction through the beta1 integrin family surface adhesion molecules VLA-4 and VLA-5 of human B-cell precursors activates CD19 receptor-associated protein-tyrosine kinases

We demonstrate that the CD19 receptor associates with the beta1 family integrin receptors on human B-cell precursors as well as mature B-lymphocytes, and engagement of the beta1 family integrin receptors with monoclonal antibody homoconjugates leads to rapid activation of the CD19-associated protein-tyrosine kinases (PTK) and results in hyperphosphorylation of CD19 on tyrosine residues. Our findings prompt the hypothesis that homoconjugate-induced integrin clustering may effect the approximation and, by intermolecular cross-phosphorylation, activation of the CD19-associated PTK and subsequent tyrosine phosphorylation of the CD19 receptor. The ability of the beta1 family integrin receptors to transmit a biochemical signal triggering the CD19-linked multifunctional PTK pathway provides a possible explanation for the pleiotropic biologic responses generated though adhesive VLA-4- and VLA-5-mediated contacts.

Chemokines regulate T cell adherence to recombinant adhesion molecules and extracellular matrix proteins

Chemokines are a family of structurally related, low m.w. proteins that regulate leukocyte migration both in vitro and in vivo. By virtue of their target cell specificity, chemokines have the potential to selectively recruit leukocyte subpopulations into sites of inflammation during the genesis of an immune response. Chemokines have been shown to induce leukocyte adhesion to endothelium, to facilitate trans-endothelial passage, and to direct cell migration along a protein gradient (chemotaxis). The chemokines (macrophage inflammatory protein-1 alpha, macrophage inflammatory protein-1 beta, RANTES, and IFN-inducible protein-10) have recently been reported to be chemotactic for T cells. We have investigated the potential activity of these proteins in regulation of T cell adhesion. These chemokines induce T cell adhesion to purified, recombinant human adhesion molecules (rhICAM-1, rhVCAM-1) and to ECM proteins: fibronectin, collagen, and laminin. The chemokine-induced adhesion process occurs rapidly, is dose-dependent, and appears to be mediated via beta 1 and beta 2 integrins. The enhanced T cell adhesion is not associated with an increased surface expression of adhesion proteins, suggesting that chemokines stimulate the development of a high affinity state in the integrin molecules. Our findings provide in vitro evidence of a critical role for chemokines in T cell adhesion to endothelial adhesion molecules and ECM proteins, thereby promoting haptotactic migration of T cells to sites of inflammation in vivo.

Expressions of very late antigen-6 and vitronectin receptor, and their interactions to laminin and vitronectin during tonsillar B-cell activation

This study examined the expressions of a-subunits of very late antigen-6 (VLA-6; alpha 6) and vitronectin receptor (VNR; alpha V) on tonsillar B cells and interactions between those integrins and their respective ligands, laminin (LM) and vitronectin (VN). alpha 6 and alpha V were expressed on about 30 to 40% of tonsillar B cells. When purified tonsillar B cells were separated by a discontinuous Percoll gradient, the number of alpha 6- and alpha V-positive cells decreased as the cell density went down, while the number of activated cells went up. After in vitro activation of tonsillar B cells by Staphylococcus aureus Cowan I strain (SAC), the expressions of alpha 6 and alpha V and their adhesiveness to LM or VN decreased significantly. Increased proliferation of B cells was observed when tonsillar B cells were cultured with immobilized LM or VN. The results of immunohistological staining showed VLA-6, VNR, LM and VN in the follicular area. These results suggest that the expressions of VLA-6 and VNR on tonsillar B cells may be decreased during B cell activation, and the interaction between VLA-6, VNR, and LM, VN may give a costimulatory effect on B cell activation in the follicular area of the tonsil.

Mononuclear leukocytes invade rabbit arterial intima during thickening formation via CD18-and VLA-4-dependent mechanisms and stimulate smooth muscle migration

The role of mononuclear leukocytes for the migration of smooth muscle cells (SMCs) during intimal thickening was investigated in the rabbit model of electrically stimulated carotid artery. The approach was to inhibit leukocyte entry into the arterial intima with antibodies against the adhesion molecules very late activation antigen-4 (VLA-4) and CD11/CD18. In electrically stimulated control rabbits treated either with saline or a nonspecific antibody, all types of granulocytes, monocytes, and lymphocytes migrated across an intact endothelium into the acellular subendothelial space, followed by the movement of SMCs from the media into the intima within 36 hours of applying electrical current. Treatment of the rabbits with monoclonal antibody (mAb) HP1/2 directed toward the alpha 4 subunit (CD49d) of VLA-4 inhibited mononuclear leukocyte invasion (consisting of monocytes and lymphocytes) by approximately 70% compared with the IgG-treated control rabbits and completely abolished the minimal influx of basophils and eosinophils after 36 hours. Neutrophil infiltration, however, remained unaffected by anti-VLA-alpha 4 treatment. Under these conditions, SMC migration across the internal elastic lamina was reduced by 50%. The use of mAb HP1/2 together with mAb 60.3 (directed to the beta 2 chain of CD11/CD18) completely abolished the influx of monocytes, lymphocytes, and all types of granulocytes into the arterial intima. This complete blockade of leukocyte infiltration resulted in a 70% reduction of intimal SMC accumulation. Together with our previous findings excluding neutrophils as stimulators of SMC migration, the present results indicate that mononuclear leukocyte promote lesion development by stimulating SMC migration.

Administration of monoclonal antibodies against vascular cell adhesion molecule-1/very late antigen-4 abrogates predisposing autoimmune diabetes in NOD mice

The interaction of vascular cell adhesion molecule-1 and very late antigen-4 (alpha 4 beta 1-integrin) has been recently known to be profoundly involved in the trafficking of lymphocytes from the circulation into the inflammatory tissues. To elucidate the role of these molecules in the development of autoimmune diabetes, the expression of these adhesion molecules on inflamed islets and the effects of administration of monoclonal antibodies to these molecules on insulitis and overt diabetes were evaluated in nonobese diabetic (NOD) mice. Immunohistochemical study revealed the overexpression of vascular cell adhesion molecule-1 on vascular endothelium near or within inflamed islets and alpha 4-integrin on islet-infiltrating mononuclear cells. Either anti-vascular cell adhesion molecule-1 or anti-alpha 4-integrin monoclonal antibody prevented the transfer of diabetes in irradiated NOD mice which received spleen cells from acutely diabetic NOD mice. When both monoclonal antibodies were administrated to NOD mice during 2-30 weeks of age, neither lymphocytic infiltration to islets nor overt diabetes was observed. Furthermore, administration of these antibodies even from 10 weeks of age could inhibit the development of insulitis and diabetes, whereas administration during 2-5 weeks of age could not. Splenocytes obtained from these treated mice showed no significant change of cytokine production and preserved the ability to transfer diabetes into NOD scid/scid mice. This suggests that treatment with antibodies against these adhesion molecules can inhibit insulitis and diabetes without affecting the Th1/Th2 balance or effector T cells. The blockade of vascular cell adhesion molecule-1/very late antigen-4 interaction would be suitable for therapeutical treatment of the predisposing and latent type I (insulin-dependent) diabetic subjects.

Bone marrow stromal cells induce myeloid and lymphoid development of the sorted hematopoietic stem cells in vitro

Regulation of development of hematopoietic stem cells was examined by culturing Lin- c-Kit+ Sca1+ stem cells sorted from bone marrow (BM) cells by fluorescence-activated cell sorting on a layer of TBR59, a BM stromal cell line established from simian virus 40 T-antigen gene transgenic mice. The sorted stem cells did not show self-renewal, but two waves (at 7 and 13 days) of a cobblestone formation were induced by the stromal cell layer. The cobblestones were formed by finite cell division (eight divisions on average) of sorted Lin- c-Kit+ Sca1+ stem cells, and divided cells were still immature. The c-Kithigh stem cell population was induced to form the first wave of cobblestone formation committed to myeloid lineage, whereas c-Kitlow population was induced to form the second wave of this formation committed to lymphoid lineage. Both cobblestone formations require c-Kit function, but very late activation antigen-4-vascular cell adhesion molecule-1 interaction plays different parts in the two lineages.

Cognate interaction between human lymphocytes and eosinophils is mediated by beta 2-integrins and very late antigen-4

Here the cognate interactions between human eosinophils and lymphocytes are studied. These interactions were measured in a double-colored FACS analysis by applying fluorescent red eosinophils (stained with hydroethidine, 40 mumol/L) and fluorescent green lymphocytes (stained with sulfidofluorescein diacetate, 100 mumol/L) in a ratio of 1:3. When normal eosinophils were mixed with a total lymphocyte preparation in stirred suspensions (37 degrees C), no physical interaction was present between both cell types. However, the addition of phytohemagglutinin and PMA resulted in a clear aggregation response between both cell types (up to 30% of the eosinophils interacted with lymphocytes after 15 minutes). CD8(+)- and CD4(+)-positive T cells contributed equally to the heterotypic aggregation response. It is interesting that when lymphocytes were pretreated with phytohemagglutinin or eosinophils with phorbol myristate acetate and subsequently washed, the cells still interacted with unstimulated counterparts. The heterotypic interaction between lymphocytes and eosinophils is blocked by monoclonal antibodies directed against the beta-chain of the beta 2-integrins (CLB LFA1/1; CD18) and the alpha-chain of very late antigen-4 (VLA-4) (HP2/1; CD49d), indicating that both the beta 2-integrins and VLA-4 contributed to this heterotypic interaction. When eosinophils bound to PHA-treated lymphocytes, the cells exhibited an activated phenotype that was characterized by an enhanced expression of CD66b and CD11b. The cells interacted with each other provided that an intact cellular metabolism was present--that is, no interaction was seen after treatment with the glycolysis inhibitor sodium mono-iodoacetate.(ABSTRACT TRUNCATED AT 250 WORDS)

Migration of human polymorphonuclear leukocytes through a synovial fibroblast barrier is mediated by both beta 2 (CD11/CD18) integrins and the beta 1 (CD29) integrins VLA-5 and VLA-6

Polymorphonuclear leukocytes (PMNL) accumulate in joint fluid in inflammatory arthritides. We investigated the molecular mechanisms required for PMNL migration through a barrier of human synovial fibroblasts (HSF) grown on microporous filters, as a model of PMNL migration through synovial connective tissue and compared this process with PMNL migration through human dermal fibroblast (HDF) barriers and through human umbilical vein endothelium (HUVE). A small amount of PMNL migration occurred spontaneously only through the synovial fibroblast/filter unit (6-10%). Migration markedly increased through all cell monolayers when the chemotactic factors C5a, IL-8, or zymosan-activated plasma (containing C5adesArg) were added to form a chemotactic gradient. The migration induced by C5a, IL-8, or C5adesArg across HSF was partially inhibited (25-76% depending on stimulus) by mAb to CD18 (beta 2 integrin). The CD18-independent migration induced by IL-8 or C5adesArg was almost completely inhibited by mAbs to beta 1 integrin, but with C5a, inhibition by mAb to beta 1 integrin was only partial (40-50%). Inhibition by mAb to beta 1 integrin required treatment of the PMNL, but not the HSF and was only observed when the function of CD11/CD18 on PMNL was also blocked by a mAb. Treatment of PMNL with mAb to alpha 5 (VLA-5) plus alpha 6 (VLA-6) in combination, was required to inhibit CD18-independent migration through HSF to the degree observed with mAb to beta 1 integrin. There was no qualitative difference in the mechanisms utilized by PMNL for migration through HSF or HDF in response to chemotactic factors. In contrast, PMNL migration across HUVE was almost completely CD18-dependent (85%) with no role for beta 1 integrins. The results suggest that (a) PMNL migration through HSF in response to chemotactic factors utilizes both CD11/CD18 and beta 1 (CD29) integrins; (b) the VLA-5 and VLA-6 members of beta 1 integrins are involved in mediating migration; and (c) PMNL utilize similar mechanisms for migration through HSF and HDF, which are distinct from migration through HUVE.

[Possible significance of VLA-4 (alpha 4 beta 1) for hematogenous metastasis of renal cell cancer]

Very late antigen-4 (VLA-4) composed of alpha 4 and beta 1, a member of the beta 1-integrin subfamily, facilitates cell-to-cell interaction with vascular cell adhesion molecule-1 (VCAM-1) on endothelial cells (EC). Attachment of blood-borne tumor cells to EC is a crucial step for hematogenous metastasis, and VLA-4-positive tumor cells can attach to EC by binding to VCAM-1. Renal cell cancer (RCC) reveals proportionally greater percentage of metastasis among other carcinomas at an initial diagnosis. We investigated whether VLA-4 is expressed on RCC and how such expression on RCC correlates with metastatic potential of RCC. Immunohistochemical staining on 66 primary and 4 metastatic RCCs showed that 4 of 4 metastatic and 5 of 8 primary RCCs (72.5%) from patients with lung and/or brain metastasis expressed alpha 4 and beta 1 chains. On the other hand, 13 of 58 (22.4%) RCCs without metastasis expressed alpha 4 chain. alpha 4 and beta 1 expressions were also detected on 5 of 5 human RCC cell lines by flowcytometer analysis. RT-PCR followed by Southern blot hybridization also confirmed mRNA production in 4 of 5 RCC cell lines. Furthermore, adhesion of alpha 4-positive RCC cell lines to human umbilical vein endothelial cells (HUVECs) was augmented by a treatment of HUVECs with Tumor necrosis factor-alpha (TNF-alpha) or IL-4 thorough increase of VCAM-1 expression. These adhesion were inhibited by anti-alpha 4 or anti-VCAM-1 antibodies suggesting that VLA-4-VCAM-1 interaction was involved in the adhesion between RCC cells and HUVECs.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac allograft survival in mice deficient in intercellular adhesion molecule-1

BACKGROUND

Intercellular adhesion molecule-1 (ICAM-1, CD54) is a cell adhesion molecule that interacts with the leukocyte beta 2 integrins, lymphocyte function-associated antigen-1, and macrophage antigen-1. ICAM-1 is postulated to play a key role in several cell-cell interactions that are important in allograft rejection, including antigen presentation, transendothelial migration of leukocytes, and leukocyte-medicated myocyte injury.

METHODS AND RESULTS

Mice homozygous for a gene-targeted mutation of ICAM-1 were used in two different cardiac transplant models to further define the role of ICAM-1 in the process of allograft rejection. In the first model, hearts from newborn mice were implanted in the ear pinnae of H-2-incompatible recipients. In the second model, intra-abdominal transplantation by direct vascular anastomosis was performed. Time to rejection was defined by the loss of pulsatile activity assessed by visual inspection in the ear model or by cessation of palpable cardiac impulse in the abdominal model. Allograft survival did not differ significantly between control groups that express normal levels of ICAM-1 and those groups using ICAM-1-deficient mutants as either donors or recipients. Histological examination of rejection of both normal and mutant (ICAM-1-deficient) cardiac allografts revealed similar patterns of infiltration of mononuclear and granulocytic leukocytes and myocyte necrosis. Immunostaining with anti-ICAM-1 antibodies showed ICAM-1-positive infiltrating cells in both mutant (ICAM-1-deficient) and normal allografts, with the graft endothelium negative for ICAM-1 staining in the mutant allografts.

CONCLUSIONS

The absence of surface expression of ICAM-1 in the donor allograft or recipient is insufficient to produce a significant impact on cardiac allograft survival. This study highlights the need to understand more precisely the mechanism of action whereby monoclonal antibodies to ICAM-1 prolong cardiac allograft survival before new therapeutic strategies based on gene transfer technology or small molecule inhibitors are developed. Mutant mice with targeted mutations in cell adhesion molecules provide powerful tools to study the complex role that cell adhesion molecules play in the cellular interactions between donor graft tissue and the recipient that culminate in graft rejection.

CD44 participates in tumor cell adhesion to endothelial cells in the experimental metastatic process in B16BL6 melanoma cells

There are several pieces of evidence suggesting a relationship between CD44 expression and tumor metastasis, but the role of CD44 in the metastatic processes is unclear. We analysed the role of CD44 in the experimental metastatic processes of B16BL6 melanoma cells using anti-CD44 monoclonal antibody (clone IM7). B16BL6 melanoma cells expressed CD44 and these cells treated with anti-CD44 monoclonal antibody increased in the experimental metastatic ability, indicating that CD44 participates in metastatic processes in B16BL6 cells. Furthermore, the adhesiveness of B16BL6 cells to endothelial cells and the retention of these cells in the lung increased by treatment with anti-CD44 monoclonal antibody. These results suggested that the CD44-mediated adhesion of tumor cells to endothelial cells was involved in the experimental metastatic process of B 16BL6 cells.

In vivo blood monocyte migration to acute inflammatory reactions, IL-1 alpha, TNF-alpha, IFN-gamma, and C5a utilizes LFA-1, Mac-1, and VLA-4. The relative importance of each integrin

The role of the monocyte integrins, Mac-1, LFA-1, and VLA-4, on the adhesion of rat blood monocytes to rat microvascular endothelial cells in vitro and the importance of these receptors in monocyte migration to inflammation in vivo were evaluated. Monocyte adhesion to cytokine (IL-1, IFN-gamma, and TNF-alpha)-stimulated endothelial cells was mediated by Mac-1, LFA-1, and VLA-4, but Mac-1 appeared to be less important than LFA-1 or VLA-4. After i.v. injection, large numbers of 51Cr-labeled blood monocytes migrated within 2 h to dermal inflammatory sites induced by C5a, IL-1 alpha, IFN-gamma, TNF-alpha, LPS, and poly inosinic:cytidylic acid. Anti-Mac-1 mAb treatment had no effect, whereas anti-LFA-1 inhibited migration to C5a and the cytokines by 20 to 40%. Blocking both Mac-1 and LFA-1 decreased monocyte accumulation by 50 to 70% to all stimuli. Anti-VLA-4 inhibited monocyte migration to IL-1 alpha, IFN-gamma, TNF-alpha, and LPS, but not to C5a. Combining anti-Mac-1 with anti-VLA-4 did not increase this inhibition, whereas blocking VLA-4 and LFA-1 together further suppressed (60-85%) migration. Combined treatment with mAb to all three integrins inhibited > 98% of the monocyte migration to the inflammatory stimuli.

IN CONCLUSION

1) 51Cr blood monocytes can be used to quantify monocyte migration to inflammatory reactions in the rat. 2) Monocytes use Mac-1, LFA-1, and VLA-4 for in vitro adhesion and in vivo migration to cutaneous inflammation, and these integrins are essential for normal migration because blockade of all three virtually abolishes monocyte accumulation. 3) Mac-1 plays a less important role than LFA-1, as LFA-1 appears to substitute for Mac-1, and VLA-4 and LFA-1 can mediate much of the adhesion and migration. 4) The initiating inflammatory stimulus also modifies monocyte integrin usage, supporting the multistep combinatorial model of leukocyte extravasation.

Expression of adhesion molecules on CD34+ cells: CD34+ L-selectin+ cells predict a rapid platelet recovery after peripheral blood stem cell transplantation

Adhesion molecules play a role in the migration of hematopoietic progenitor cells and regulation of hematopoiesis. To study whether the mobilization process is associated with changes in expression of adhesion molecules, the expression of CD31, CD44, L-selectin, sialyl Lewisx, beta 1 integrins very late antigen 4 (VLA-4) and VLA-5, and beta 2 integrins lymphocyte function-associated 1 and Mac-1 was measured on either bone marrow (BM) CD34+ cells or on peripheral blood CD34+ cells mobilized with a combination of granulocyte colony-stimulating factor (G-CSF) and chemotherapy. beta 1 integrin VLA-4 was expressed at a significantly lower concentration on peripheral blood progenitor cells than on BM CD34+ cells, procured either during steady-state hematopoiesis or at the time of leukocytapheresis. No differences in the level of expression were found for the other adhesion molecules. To obtain insight in which adhesion molecules may participate in the homing of peripheral blood stem cells (PBSCs), the number of CD34+ cells expressing these adhesion molecules present in leukocytapheresis material was quantified and correlated with hematopoietic recovery after intensive chemotherapy in 27 patients. The number of CD34+ cells in the subset defined by L-selectin expression correlated significantly better with time to platelet recovery after PBSC transplantation (r = -.86) than did the total number of CD34+ cells (r = -.55). Statistical analysis of the relationship between the number of CD34+L-selectin+ cells and platelet recovery resulted in a threshold value for rapid platelet recovery of 2.1 x 10(6) CD34+ L-selectin+ cells/kg. A rapid platelet recovery (< or = 14 days) was observed in 13 of 15 patients who received > or = 2.1 x 10(6) CD34+ L-selectin+ cells/kg (median, 11 days; range, 7 to 16 days), whereas 10 of 12 patients who received less double positive cells had a relative slow platelet recovery (median, 20 days; range, 13 to 37 days). The L-selectin+ subpopulation of CD34+ cells also correlated better with time to neutrophil recovery (r = -.70) than did the total number of reinfused CD34+ cells (r = -.51). However, this latter difference failed to reach statistical significance. This study suggests that L-selectin is involved in the homing of CD34+ cells after PBSC transplantation.

T lymphocyte adhesion to human brain pericytes is mediated via very late antigen-4/vascular cell adhesion molecule-1 interactions

T cell adhesion to the brain microvascular endothelium and subsequent migration into the brain parenchyma is one of the major events in the development of multiple sclerosis (MS). Interactions of the T cell integrin very late antigen-4 (VLA-4) with its receptor, vascular cell adhesion molecule-1 (VCAM-1) have been described to be of crucial importance for the development of MS. We investigated the expression of these adhesion molecules in MS brain tissue by immunohistochemical analysis, and studied their functional involvement in an in vitro T cell adhesion assay. A number of other adhesion molecules were studied for comparison. In cryosections of several MS brains, expression of VCAM-1 was demonstrated not only on the endothelium of vessels surrounding MS plaques, but also in perivascular positions, suggesting expression by pericytes. T cells adhered to both cell types in vitro. Both LFA-1/intercellular adhesion molecule-1 and VLA-4/VCAM-1 interactions were equally involved in the adhesion of T cells to TNF-alpha-stimulated endothelial cells. However, adhesion of T cells to TNF-alpha-stimulated pericytes was clearly dominated by VLA-4/VCAM-1 interactions. These results indicate that pericytes, next to endothelial cells, may play an important role in regulating T cell infiltration into the central nervous system.

T lymphocyte locomotion in a three-dimensional collagen matrix. Expression and function of cell adhesion molecules

T cell locomotion within the extracellular matrix may be mediated by cell adhesion molecules. We investigated the expression and function of beta 1- and beta 2-integrins and CD44 on human peripheral CD4+ and CD8+ lymphocytes locomoting in a 3-D type I collagen matrix. Paths of randomly selected T cells were digitized from time-lapse videorecordings and were quantitatively analyzed. After the blocking of CD49b with mAb Gi9, the locomotion of a defined locomotor subset (50% of spontaneously locomoting cells) was inhibited. Anti-CD49d mAb HP2/1 and an activating anti-CD44 mAb (J173), respectively, induced transient recruitment (< 1 h) of previously nonmotile cells (10 to 35%). In contrast to the J173-induced short-term locomotion, hyaluronan incorporated within the matrix promoted locomotion for > 2 h. No significant effects were present for anti-CD49f (GoH3) and -CD11a (25.3) mAbs. After the addition of IL-8 to the matrix, rapid induction of locomotion in 20 to 30% of the cells (control) was evident, which was virtually abolished by anti-alpha 2- and alpha 6-integrin, and -CD11a mAbs. Thus, the locomotion of nonactivated and IL-8-activated T cells may involve different sets of integrins. Using flow cytometry, the development of a CD49b+CD29highCD44lowL-selectinlow T cell phenotype independent of activation markers including CD25, CD27, CD28, VLA-4, and CD45RA- to CD45RO-transition was observed after 4 days in the matrix. The initial development of spontaneous locomotion in the collagen matrix, however, was not accompanied by alterations in CAM surface staining and, therefore, may involve functional CAM activation rather than involving an increase in surface expression.

Cytokines increase human hemopoietic cell adhesiveness by activation of very late antigen (VLA)-4 and VLA-5 integrins

Cytokines are known to be important regulators of normal hemopoiesis, acting in concert with components of the bone marrow microenvironment. Interactions with this microenvironment are known to regulate the proliferation, differentiation, and homing of hemopoietic progenitor (CD34+) cells. Adhesive interactions with the extracellular matrix retain CD34+ cells in close proximity to cytokines, but may also provide important costimulatory signals. Thus, the functional states of adhesion receptors are critical properties of CD34+ cells, but the physiological mechanisms responsible for regulating functional properties of cell adhesion receptors on primitive hemopoietic cells are still unknown. We confirm that the integrins very late antigen (VLA)-4 and VLA-5 are expressed on the CD34+ cell lines MO7e, TF1, and on normal bone marrow CD34+ progenitor cells, but in a low affinity state, conferring on them a weak adhesive phenotype on fibronectin (Fn). Herein, we show that the cytokines interleukin (IL)-3, granulocyte-macrophage CSF (GM-CSF), and KIT ligand (KL) are physiological activators of VLA-4 and VLA-5 expressed by MO7e, TF1, and normal bone marrow CD34+ progenitor cells. Cytokine-stimulated adhesion on Fn is dose dependent and transient, reaching a maximum between 15 and 30 min and returning to basal levels after 2 h. This cytokine-dependent activation is specific for VLA-4 and VLA-5, since activation of other beta 1 integrins was not observed. The addition of second messenger antagonists staurosporine and W7 abolished all cytokine-stimulated adhesion to Fn. In contrast, genistein inhibited KL-stimulated adhesion, but failed to inhibit GM-CSF- and IL-3-stimulated adhesion. Our data suggest that cytokines GM-CSF and IL-3 specifically stimulate beta 1 integrin function via an "inside-out" mechanism involving protein kinase activity, while KL stimulates integrin activity through a similar, but initially distinct, pathway via the KIT tyrosine-kinase. Thus, in addition to promoting the survival, proliferation, and development of hemopoietic progenitors, cytokines also regulate adhesive interactions between progenitor cells and the bone marrow microenvironment by modifying the functional states of specific integrins. These data are of importance in understanding the fundamental processes of beta 1 integrin activation and cellular response to mitogenic cytokines as well as on the clinical setting where cytokines induce therapeutic mobilization of hematopoietic progenitors.

The adhesion molecules used by monocytes for migration across endothelium include CD11a/CD18, CD11b/CD18, and VLA-4 on monocytes and ICAM-1, VCAM-1, and other ligands on endothelium

CD11/CD18 and VLA-4 integrins mediate interactions of monocytes with HUVEC cultured on human amniotic tissue. In the present study, the roles of individual CD11/CD18 integrins and endothelial adhesion molecules were examined using blocking mAbs and peptides. After 20 min of incubation, monocyte adhesion to and migration across unstimulated endothelium was dependent primarily on CD11a/CD18. When incubation was extended to 2 h to allow for completion of migration, either CD11a/CD18 or CD11b/CD18 could be used. Similarly, either CD11a/CD18 or CD11b/CD18 could be used by monocytes to bind to and traverse IL-1 beta-stimulated endothelium. Although both CD11a/CD18 and CD11b/CD18 are known to bind to ICAM-1, results of Ab-mixing experiments suggest that alternative ligands on HUVEC for CD11/CD18 integrins also may be used during transendothelial migration of monocytes. Our previous studies indicate that VLA-4 on monocytes interacts primarily with VCAM-1 on unstimulated endothelium. In contrast, migration of monocytes across IL-1 beta-stimulated endothelium was less dependent on VCAM-1. mAbs directed against binding sites for VLA-4 in domain 1 and domain 4 of VCAM-1 did not, by themselves, inhibit interactions of monocytes with stimulated HUVEC. VLA-4-dependent migration across IL-1 beta-stimulated endothelium was markedly inhibited only when mAbs to VCAM-1 were added in combination with peptides of fibronectin. Therefore, VLA-4 can interact with either VCAM-1 or alternative ligands on IL-1 beta-stimulated HUVEC-amnion cultures to mediate transendothelial migration of monocytes.

Monocyte migration to arthritis in the rat utilizes both CD11/CD18 and very late activation antigen 4 integrin mechanisms

In human and experimental models of arthritis, blood monocytes migrate into the inflamed synovium and joint space. The mechanisms required for monocyte migration across the vascular endothelium in joints is poorly defined. Radiolabeled rat blood monocytes were used to measure monocyte migration to the inflamed joints of rats with adjuvant arthritis, and the role of monocyte adhesion molecules was analyzed. Monocyte accumulation in the inflamed joints was maximal 14-21 d after immunization with adjuvant, when arthritis had fully developed. Blocking mAbs to lymphocyte function-associated antigen 1 (LFA-1), Mac-1, and very late activation antigen 4 (VLA-4) were used to evaluate the role of these integrins in the migration. Migration to the joints was not inhibited by treatment of the animals with mAb to LFA-1, Mac-1, or VLA-4 alone, and was partially (50%) inhibited in only the most arthritic joint, the talar joint, by the combination of mAb to LFA-1 plus Mac-1. In contrast, this combination inhibited migration to dermal inflammation induced by C5ades Arg, endotoxin, tumor necrosis factor alpha, and polyinosine-cytosine by 60-70%. When mAbs to LFA-1 and VLA-4 were combined, migration to all the inflamed joints was strongly inhibited (80-98%, depending on the joint). Treatment with the combination of the three mAbs to LFA-1, Mac-1, and VLA-4 completely eliminated monocyte migration to all joints and dermal inflammation. The results show that 51Cr blood monocytes can be used to quantify monocyte migration to arthritic joints in the rat. LFA-1 alone or VLA-4 alone is sufficient to mediate most of this migration, and either LFA-1 or VLA-4 is required for monocyte migration to joint inflammation. These results indicate that both the VLA-4 and LFA-1 integrins should be therapeutic targets for suppression of monocyte infiltration of joints in arthritis.

Role of VLA-4 and LFA-1 in allergen-induced airway hyperresponsiveness and lung inflammation in the rat

The aim of the study was to evaluate the effects of blocking the integrins VLA-4 and LFA-1 on allergen-induced airway eosinophilia and responsiveness in Brown-Norway rats. Ovalbumin-sensitized rats were exposed to either aerosols of ovalbumin or saline. Airway responsiveness to methacholine (MCh) was determined 8 and 32 h after challenge. Cellular populations in the lung lavage and lung tissues were determined 32 h after allergen challenge. Total numbers of eosinophils were increased in the lung lavage (25 ml) and the small airways/parenchyma in the ovalbumin (OA)-challenged rats (4.37 x 10(6) +/- 0.71 and 15.54 x 10(6) +/- 1.99, respectively) compared with the saline-challenged rats (0.99 x 10(6) +/- 0.81 and 4.84 x 10(6) +/- 2.27; p < 0.05). Animals treated with both anti-VLA-4 and anti-LFA-1 mAbs and with anti-LFA-1 mAb alone had reduced numbers of eosinophils in the lung lavage (0.76 x 10(6) +/- 0.80 and 0.40 x 10(6) +/- 1.14, respectively; p < 0.05) and in the small airways/parenchyma (8.64 x 10(6) +/- 2.07 and 4.44 x 10(6) +/- 3.20; p < 0.05). Anti-VLA-4 mAb treatment alone did not alter the eosinophils recovered from the lung. Airway responsiveness to methacholine increased from 8 to 32 h in all ovalbumin-challenged rats, but treatment with anti-VLA-4, anti-LFA-1, or both mAbs prevented the increase in responsiveness. In conclusion, allergen-induced airway hyperresponsiveness is inhibitable by blocking either VLA-4 or LFA-1 integrins and is associated with a lung eosinophilia that is LFA-1 dependent and VLA-4 independent.(ABSTRACT TRUNCATED AT 250 WORDS)

Migration of skin-homing T cells across cytokine-activated human endothelial cell layers involves interaction of the cutaneous lymphocyte-associated antigen (CLA), the very late antigen-4 (VLA-4), and the lymphocyte function-associated antigen-1 (LFA-1)

The cutaneous lymphocyte-associated Ag (CLA) is expressed by a subset of circulating memory/effector T cells and by the vast majority of skin-infiltrating T cells. CLA is thought to target skin-associated T cells to inflammatory skin sites by interacting with endothelial cell ligand E-selectin (CD62E). We have examined adhesion molecules involved in the migration of human CLA+ and CLA- memory/effector T lymphocytes through IL-1- and TNF-alpha-activated and nonactivated HUVEC layers under static (nonflow) conditions. CLA-enriched memory/effector T lymphocytes migrated more actively across cytokine-activated HUVEC than CLA-depleted memory/effector T cells. This enhanced migration is dependent on the CLA/E-selectin interaction. mAb to very late Ag-4 (VLA-4) and vascular cell adhesion molecule-1 (VCAM-1) blocked the migration of CLA-enriched, but not of CLA-depleted, T cells across activated HUVEC. The observation that anti-VLA-4 and anti-CLA mAb did not show additional inhibition supports the concept that CLA and VLA-4 are sequentially involved in the extravasation. The fact that only CLA+ T cells were inhibited by the anti-VLA-4 mAb suggests that, in this system, CLA engagement is required for using the VLA-4/VCAM-1 pathway. Our studies demonstrate that CLA+ T cells use LFA-1/intercellular leukocyte adhesion molecule-1 (ICAM-1) for transmigration but that CLA expression is not required for the LFA-1/ICAM-1-dependent transmigration because anti-CD18/CD11a mAbs and anti-ICAM-1 mAbs were able to block T cell migration regardless of the activation state of HUVEC or the CLA expression by T cells. Taken together, our results suggest that CLA has a homing function in conducting the T cell to interact with LFA-1/ICAM-1 and/or VLA-4/VCAM-1; this results in enhanced adhesion and migration across cytokine-activated endothelial cells.

Cell spreading in Colo 201 by staurosporin is alpha 3 beta 1 integrin-mediated with tyrosine phosphorylation of Src and tensin

Staurosporin, a broad-spectrum kinase inhibitor, induced cell spreading in a human colon cancer cell line, Colo 201. On collagen and laminin, cell spreading was induced in more than 90% of the cells and was dependent on very late activation antigen-3, as shown by an antibody inhibition assay. Cell spreading required divalent cations and showed the order of preference Mn2+ > Mg2+ > Ca2+. On fibronectin, only about 30% of the cells were observed to spread, and spreading occurred via a non-integrin, RGD-independent pathway. Staurosporin-induced spreading was inhibited by treatment with tyrosine kinase inhibitors herbimycin A and methyl 2,5-dihydroxycinnamate. Despite the presence of staurosporin, seven proteins (220, 175, 150, 98, 62, 58, and 45 kDa) showed increased levels of tyrosine phosphorylation in association with cell adhesion. Two of these (58 and 220 kDa) were identified by immunoprecipitation as Src product and tensin, respectively. Flow cytometric analysis showed that the Colo 201 cells expressed the alpha 2, alpha 3, alpha 6, and beta 1 chains of integrin, but expression of these chains was not influenced by staurosporin. Immunofluorescence microscopy revealed that the alpha 3 chain, diffusely expressed on the cell surface in the absence of staurosporin, was concentrated at focal adhesion plaques after staurosporin treatment. Neither alpha 2 nor alpha 6 was focalized by the treatment.

Involvement of the very late antigen 4 integrin on melanoma in interleukin 1-augmented experimental metastases

We have previously reported that treatment with interleukin 1 (IL-1) induced the augmentation of lung tumor colonies by a human melanoma in nude mice. Here we have investigated the involvement of the alpha 4 beta 1 integrin, the very late antigen 4 (VLA-4) in this augmentation. A375M melanoma cells expressed high levels of VLA-4 and preferentially adhered to a surface coated with vascular cell adhesion molecule 1 (VCAM-1), the ligand for VLA-4 on activated endothelial cells. This adhesion was inhibited by treating tumor cells with saturating concentrations of mAb to VLA-4. The production of lung colonies was significantly enhanced in nude mice given an injection of IL-1 before A375M melanoma cells. Immunoperoxidase staining showed that VCAM-1 could be expressed on lung vascular endothelium of mice in response to IL-1. Pretreatment of melanoma cells with a mAb to VLA-4 completely abrogated the IL-1-induced augmentation of lung colonies. Using two metastatic melanoma clones (clones 2/4 and 2/60) that expressed different levels of VLA-4, we found that only VLA-4-bearing cells adhered to a VCAM-1-coated surface and formed enhanced numbers of lung colonies in IL-1-treated nude mice. This augmentation was inhibited by pretreating the tumor cells with anti-VLA-4 mAb. These results demonstrate, in vivo, the functional involvement of VLA-4 on melanoma cells in IL-1-mediated lung colony augmentation, most probably involving the interaction of tumor cells with VCAM-1 on activated endothelial cells.

Heterotypic adherence between human B-lymphoblastic and pre-B-lymphoblastic cells and marrow stromal cells is a biphasic event: integrin very late antigen-4 alpha mediates only the early phase of the heterotypic adhesion

Heterotypic adherence between marrow stromal cells (MSC) and lymphoblastic cells is essential for normal lymphopoiesis and malignant lymphoblastic development. However, the detailed molecular mechanisms by which this heterotypic adherence occurs are poorly understood. The cell-cell interactions between a B-lymphoblastic cell line (UTMB-460) and a pre-B-cell line (NALM-6) with MSC were chosen as models to investigate potential mechanisms and adhesion molecules involved in the apposition between normal and malignant lymphoblastic cells and MSC. A parallel-flow detachment assay (PFDA) and a 51Cr detachment assay, coupled with monoclonal antibody (MoAb) blocking experiments, were used to quantify the attachment of lymphoblastic cells to confluent monolayers of MSC. The apposition between MSC and B-lymphoblastic cells (UTMB-460 cells) was investigated for variable time periods, ranging from 1 minute to 4 hours. Results from the temporal study suggest that the heterotypic adherence of the B-lymphoblastic cells to MSC is a biphasic event and the interactions occur rapidly (< or = 1 minute) after the two cells come into contact. More specifically, the early phase of adherence (< or = 15 minutes) solely involves very late antigen-4 alpha (VLA-4 alpha)/vascular cell adhesion molecule 1 (VCAM-1) interactions, as evidenced by the nearly complete inhibition (93%) of UTMB-460 cell adherence in the presence of anti-VLA-4 alpha. The late phase (> or = 30 minutes) proceeds despite the continuous presence of anti-VLA-4 alpha. In addition, the late-phase adherence is not affected by MoAbs to LFA-1, CD44, VCAM-1, E-selectin, or L-selectin, which suggests the possible involvement of other adhesion molecules. Adherence of pre-B-lymphoblastic cells (NALM-6) to MSC is also biphasic. Integrin VLA-4 is again a major player in the early phase of pre-B-lymphoblastic cell/MSC interactions. The early phase of adherence may be important in homing of the malignant lymphoblastic cells to the MSC and the late phase in retention of malignant lymphoblastic cells in the bone marrow.

Monocyte adhesion to cerebromicrovascular endothelial cells derived from hypertensive and normotensive rats

The stroke risk factor hypertension may function as a predisposing agent by increasing the vulnerability of blood vessels to thrombosis or hemorrhage. The research here demonstrates that cerebrovascular endothelial cells (EC) from spontaneously hypertensive (SHR) and Wistar-Kyoto normotensive (WKY) rats exhibit similar levels of adhesiveness for syngeneic peripheral blood monocytes (e.g., 22.53 +/- 1.32 and 24.35 +/- 1.16%, respectively). Monocyte adhesion to SHR EC was dramatically increased by treatment of EC with lipopolysaccharide, interferon-gamma, or interleukin-1 beta and tumor necrosis factor-alpha (e.g., 106, 68, and 171%, respectively). Identical treatment of WKY EC also increased adhesion albeit at significantly lower levels than observed on concomitantly tested SHR EC (e.g., 47.8, 12.7, and 60.7%, respectively). Allogeneic combinations of monocytes and EC again demonstrated significantly more upregulation of adhesion by treatment of SHR EC than WKY EC. Characterization of these adhesive interactions revealed the interplay of adhesion pathways, which include lymphocyte functional antigen-1/intercellular adhesion molecule-1 (ICAM-1), Mac-1/ICAM-1, and very late activation antigen-4/vascular adhesion molecule-1 as well as other undetermined mechanisms. In summary, these findings indicate hypertension may enhance responsiveness of endothelium to factors that promote monocyte adhesion.

The VLA-2 (alpha 2 beta 1) I domain functions as a ligand-specific recognition sequence for endothelial cell attachment and spreading: molecular and functional characterization

The integrin VLA-2 (alpha 2 beta 1), generally considered to represent the specific collagen receptor on human endothelial cells, contains an alpha 2-subunit inserted I domain with structural similarity to the type A domains found within the recently described superfamily of receptor-ligand recognition proteins. This region of the cDNA has now been isolated and used for molecular and functional characterization of this heterodimeric receptor complex. Comparative sequence analysis with the porcine homologue revealed 93% amino acid sequence identity, suggestive of a developmentally conserved function. To complete structure/function studies, this region of the human cDNA was expressed as a chimeric protein in Escherichia coli, and a rabbit polyclonal antibody (anti-I domain) was used to study determinants of endothelial cell attachment and spreading in vitro. Quantifiable and visual disruption of endothelial cell attachment to gelatin, type I collagen, and laminin was evident using the specific anti-I domain antibody, with minimal inhibitory effects demonstrable using fibronectin or fibrinogen matrices. Therefore, these data would suggest that the alpha 2 beta 1 I domain confers ligand-binding specificity for both known alpha 2 beta 1 substrates (laminin and collagen), and that this region subserves a regulatory function in the molecular processes controlling endothelial cell attachment and spreading in vitro.

Signals from platelet/endothelial cell adhesion molecule enhance the adhesive activity of the very late antigen-4 integrin of human CD34+ hemopoietic progenitor cells

Adhesive interactions between human CD34+ hemopoietic progenitor cells and bone marrow stromal cells control the localization, proliferation, and differentiation of CD34+ cells. Changes in adhesive interactions may contribute to the mobilization of CD34+ cells to the blood induced by chemotherapy and cytokines. Thus, the identities and functional states of adhesion receptors are critical properties of CD34+ cells. Here, we confirm that the adhesion receptors very late antigen-4 (VLA-4), LFA-1, and platelet/endothelial cell adhesion molecule-1 (PECAM-1) are expressed on the CD34+ cell line KG1a and on CD34+ normal, steady state bone marrow cells. Therapeutically mobilized CD34+ cells express similar levels of PECAM-1 but reduced levels of VLA-4 and LFA-1 in comparison with steady state bone marrow cells. Integrin adhesive activity was measured from the binding of PKH 26- or phycoerythrin-labeled CD34+ cells to FITC-labeled Chinese hamster ovary (CHO) cells expressing vascular CAM-1 (VCAM-1) or intercellular CAM-1, which are ligands for VLA-4 and LFA-1, respectively. Incubation mixtures were analyzed by flow cytometry for the loss of free CD34+ cells and gain of CD34(+)-CHO cell aggregates. VLA-4 mediates the strong and specific adhesion of KG1a cells and bone marrow CD34+ cells to VCAM-1-transfected CHO cells. CD34+ cells mobilized with granulocyte colony stimulating factor (G-CSF) or cyclophosphamide also bind VCAM-1 via VLA-4. The VLA-4-mediated adhesion of all CD34+ cells to VCAM-1 is enhanced by Abs to the coexpressed adhesion receptor PECAM-1, implicating signals transmitted from PECAM-1 as determinants of VLA-4 integrin activity. VLA-4 function in CD34+ cells mobilized with G-CSF or cyclophosphamide is equivalent to steady state CD34+ cells. LFA-1 mediates minimal adhesion between CD34+ cells and intercellular CAM-1 transfected CHO cells and is refractory to PECAM-1 modulation. We infer that VLA-4, but not LFA-1, contributes to the constitutive adhesive phenotype of CD34+ cells. PECAM-1 is probably one of several receptors that control adhesive interactions between hemopoietic progenitors and target cells by regulating the activation states of specific integrins.

Immunohistological and functional analysis of adhesion molecule expression in the rheumatoid synovial lining layer. Implications for synovial lining cell destruction

OBJECTIVE

It has previously been shown that the adhesion of lymphocytes to microvascular endothelium mediates lymphocyte extravasation within inflamed synovium. After passing the endothelial barrier, binding of lymphocytes to matrix proteins and synovial lining cells may further lead to synovial membrane hyperplasia and subsequent cartilage destruction. Thus, we have explored the molecular basis of T cell-synovial lining cell interaction in the synovial membrane of patients with rheumatoid arthritis (RA).

METHODS

Using an immunohistochemical staining technique and an in vitro frozen section assay we studied the expression and the role of several adhesion molecules in T lymphocyte-synovial lining cell interaction in the inflamed synovial membrane.

RESULTS

In RA the macrophage-like (type A) synovial lining cells express high levels of intercellular adhesion molecule 1 [ICAM-1 (CD54)], whereas the fibroblast-like (type B) synovial lining cells predominantly express vascular cell adhesion molecule 1 (VCAM-1), in addition to moderate levels of ICAM-1. Both cell types express low levels of fibronectin. Unstimulated and anti-CD3 stimulated peripheral blood T cells bear the respective ligands lymphocyte function associated antigen 1 [LFA-1 (CD18/11a)], and very late antigen 4 and 5 [VLA-4 (CD29/49d) and VLA-5 (CD29/49e)]. T lymphocytes predominantly bound to type B synovial lining cells. Inhibition studies with monoclonal antibodies revealed that this binding involves the VLA-4/VCAM-1 and VLA-5/fibronectin (FN), but not the VLA-4/CS1 pathway. LFA-1 is also involved in this interaction via its ligand ICAM-1.

CONCLUSION

These results show that the molecular basis of T lymphocyte binding to rheumatoid synovial lining cells is different from that described for T lymphocyte binding to synovial membrane vascular endothelium which involves the VLA-4/VCAM-1 and VLA-4/CS-1 pathways, but not the LFA-1/ICAM-1 pathway.

L-selectin and very late antigen-4 integrin promote eosinophil rolling at physiological shear rates in vivo

Adherence of eosinophils to vascular endothelium and their accumulation at sites of allergen challenge are hallmarks of allergic inflammation. However, the molecular mechanisms mediating eosinophil adhesion under conditions of blood flow are not well understood. The present studies were performed to identify the receptors on human eosinophils involved in initiating adhesion to activated endothelium at physiologic shear rates in vivo. We have compared the relative contribution of L-selectin, VLA-4 (CD49d), and CD18 integrins in mediating eosinophil adhesion to microvascular endothelial cells in the rabbit mesentery by using intravital video microscopy. Eosinophils were found to roll in venules, but not arterioles, and this rolling could be stimulated by activation of endothelium with IL-1. In contrast to neutrophil rolling, which is predominantly L-selectin-dependent, eosinophil rolling was mediated by L-selectin, and also VLA-4. mAbs to L-selectin and VLA-4 alpha, but not CD18, significantly inhibited eosinophil rolling in vivo. The inhibition of VLA-4-mediated eosinophil rolling was not caused by modulation of eosinophil L-selectin or CD18 expression. This inhibition also was not caused by nonspecific inhibitory effect of the Abs studied, because the anti-VLA-4 mAbs inhibited eosinophil (VLA-4+) but not neutrophil (VLA-4-) rolling in the mesenteric venules. These results demonstrate that early events of eosinophil adhesion, i.e., rolling, are mediated by multiple adhesion receptors, including L-selectin and VLA-4, at physiologic shear rates in vivo.

Molecular signals for the production of lymphocytes in bone marrow

Bone marrow culture and molecular cloning techniques have permitted rapid progress to be made in identifying molecules that stimulate or inhibit particular steps in blood cell formation. Two types of factors that influence B lymphocyte precursors are considered in this brief review. Cell adhesion molecules are probably needed to correctly position immature precursors within the marrow and some of the most important of these have been identified. Recent studies suggest that local or systemically derived hormones must also be added to the list of agents which can markedly influence the production of lymphocytes.

Role of LFA-1, CD2, VLA-5/CD29, and CD43 surface receptors in CD4+ T cell adhesion to B cells

We investigated the adhesion to B cells of CD4+ T cells both in the resting state and following activation by CD3 cross-linking or stimulation by PMA/ionomycine/IL2 for 6 days. Both resting and activated CD4+ T cell adhesion were inhibited by anti-LFA-1, -CD2, -VLA-5/CD29, and -CD43 antibodies, suggesting coordinated upregulation of T cell adhesion. The CD2 and LFA-1 adhesion pathways were found to act independently, as CD2 was functional in T cells not expressing LFA-1, and vice versa, and as specific antibodies had additive effects. In contrast, LFA-1- and VLA-5/CD29-specific antibodies did not have an additive blocking effect on CD4+ T cell adhesion, suggesting that efficient adhesion requires a competitive association of integrins with cytoskeleton elements. Although the involvement of fibronectin (coated to B cells via VLA-4) in VLA-5-mediated T cell adhesion to B cells is feasible, an anti-fibronectin and a VLA-4-specific antibody had no blocking effect. The involvement of an unidentified B cell ligand can also be envisaged.

The I domain is essential for echovirus 1 interaction with VLA-2

VLA-2, the alpha 2 beta 1 integrin, mediates cell adhesion to collagen and laminin, and is the receptor for the human pathogen echovirus 1. Because of its similarity to domains present in other proteins that interact with collagen, a 191 amino acid region within the alpha 2 subunit (the I domain) has been proposed as a potential site for ligand interactions. Although the alpha 2 subunits of human and murine VLA-2 are 84% identical, human alpha 2 promotes virus binding whereas murine alpha 2 does not. We used murine/human chimeric alpha 2 molecules to identify regions of the human molecule essential for virus binding. Virus bound efficiently to a chimeric protein in which the human I domain was inserted into murine alpha 2, indicating that the human I domain is responsible for specific virus interactions. Monoclonal antibodies that inhibited virus attachment all recognized epitopes within the human I domain, further suggesting that virus interacts with this portion of the molecule. Similarly, antibodies that prevented VLA-2-mediated cell adhesion to collagen also mapped to the I domain. These results indicate that the I domain plays a role in VLA-2 interactions both with virus and with extracellular matrix ligands.

Lymphocyte traffic and positioning in vivo: an expanded role for the ECM, the VLA proteins and the cytokines

The continuous circulation of lymphocytes between blood and lymph, constitutes, with the specific recognition of foreign antigens and with memory, one of the hallmarks of the immunological system. In the routine process of recirculating between blood and lymph in adult life, lymphocytes display the unique capacity of recognizing "self within self". The physiological recognition of "self within self" is expressed at three levels: (1) an overall ability to distinguish between peripheral lymphoid and non-lymphoid organs, (2) the ability of lymphocyte subpopulations to discriminate between peripheral lymphoid organs, (3) a fine recognition of distinct microenvironments within the peripheral lymphoid organs. Historically, interest in regulation of entry into the lymph dominated this field, focusing primarily on the interaction of lymphocytes with post-capillary venules with high endothelium found in some higher vertebrate lymph nodes. Lymphocytes, however, enter the lymph in species without lymph nodes, and lymphocytes recirculation is well established in fetal life. Regardless of route of entry, lymphocytes in birds, fish, rodents, and humans enter the peripheral lymphoid organs and display the capacity to segregate and arrange themselves in distinct territories, a phenomenon called "ecotaxis". This paper reviews the evidence for the relative contribution of so called specialized lymphocyte endothelium interactions and other interactions, to the physiological regulation of lymphocyte traffic and positioning. Of the latter, interactions of lymphocytes with the ECM appear of some significance for two reasons: there is a selective distribution of some ECM components in peripheral lymphoid organ areas, as recently shown for tenascin in the thymus-dependent zones (Chilosi et al., Am J Pathol 143: 1348-1355, 1993). This selective distribution may serve as a basis for preferential T cell migration through those zones. The abnormal expression of tenascin in non-lymphoid organs with autoimmune lesions may serve as an identical basis for abnormal T lymphocyte migration in autoimmunity (Chilosi, personal communication). Additional evidence for abnormal cell-ECM interactions playing a role in autoimmune-like lesions comes from the recent observations in TGF-beta 1 knockout mice, in which mononuclear cell infiltration of the heart and lungs has been corrected by the systemic administration of synthetic FN peptides (Hines at al., PNAS 91:5187-5191, 1994). Changes in expression of ECM components have aso being described in rat heart allografts preceding lymphocyte accumulation in the process of allograft rejection (Coito et atl. Transplantation 57:599-605, 1994).(ABSTRACT TRUNCATED AT 400 WORDS)

Coengagement of CD2 with LFA-1 or VLA-4 by bispecific ligand fusion proteins primes T cells to respond more effectively to T cell receptor-dependent signals

To examine the effects of ligand engagement and accessory molecule juxtaposition on T cell receptor (TCR) signaling, we prepared LFA-3/ICAM-1 Rg and LFA-3/VCAM-1 Rg bispecific immunoglobulin fusion proteins (Rg, recombinant globulin). These novel fusion proteins allowed us to examine the effects of ligand driven co-engagement of T cell proteins CD2 and LFA-1 or CD2 and VLA-4 on TCR-dependent mobilization of intracellular Ca2+. We observed that preincubation of resting T cells with LFA-3/ICAM-1 Rg or LFA-3/VCAM-1 Rg fusion proteins resulted in significantly enhanced mobilization of intracellular Ca2+ following TCR-accessory molecule cross-linking relative to T cells preincubated with each of the monospecific Rgs alone or with combinations of the monospecific Rg fusion proteins. In addition, such coengagement stimulated TCR-dependent activation and tyrosine phosphorylation of phospholipase C gamma 1 (PLC gamma 1). These results suggest that when T cells interact with antigen presenting cells the engagement of multiple cell adhesion molecules such as CD2, LFA-1, and VLA-4 primes the T cell to respond more effectively to signals delivered through the TCR.

B and T lymphocyte subsets enter peripheral lymph nodes and Peyer's patches without preference in vivo: no correlation occurs between their localization in different types of high endothelial venules and the expression of CD44, VLA-4, LFA-1, ICAM-1, CD2 or L-selectin

Many lymphocytes enter tissues such as peripheral lymph nodes, and Peyer's patches through high endothelial venules (HEV). It is known that HEV differ in the expression of adhesion molecules as lymphocyte subsets do. Through the interaction of these molecules B and T lymphocyte subsets are thought to be preferentially directed into lymphoid organs. However, it is unclear which role these mechanisms play in vivo, since there are no studies demonstrating that blood lymphocyte subsets preferentially interact with different types of HEV in vivo. Therefore, in the present study the frequency of B, T, CD4+ and CD8+ lymphocytes in the wall of the HEV of rat peripheral lymph nodes and Peyer's patches was analyzed by immunohistology. In addition, the expression of CD44, VLA-4, LFA-1, ICAM-1, CD2 and L-selectin on B and T lymphocyte subsets of the blood was determined by flow cytometry. Although B and T lymphocytes showed significantly different levels of expression for each adhesion molecule investigated, the relation of B and T lymphocytes within the HEV of peripheral lymph nodes and Peyer's patches was strikingly comparable (38.0 +/- 5.2% vs. 40.6 +/- 5.7% and 62.0 +/- 5.2% vs. 59.4 +/- 5.7%, respectively). The same was true for CD4+ and CD8+ cells. Thus, although HEV and the blood lymphocyte subsets differ markedly in their expression pattern of adhesion molecules, the existing levels are sufficient to mediate comparable entrance of B and T lymphocyte subsets into both types of HEV.