T-cell receptor cross-linking transiently stimulates adhesiveness through LFA-1

Engagement of major histocompatibility complex class II molecules induces sustained, lymphocyte function-associated molecule 1-dependent cell adhesion

Antigenic stimulation is associated with enhanced adhesion between T cells and antigen-presenting cells (APC). Binding of ligands to the T cell antigen receptor activates the adhesion function of lymphocyte function-associated molecule 1 (LFA-1; CD11a/CD18). We demonstrate here that ligand binding to major histocompatibility complex class II (Ia) molecules also activates LFA-1 function, providing a reciprocal mechanism for the induction of adhesion between T cells and Ia+ APC. Adhesion was affected by a qualitative change in LFA-1 molecules and was reversed by the protein kinase C inhibitor sphingosine. These results define a novel role for Ia molecules as signal transducing receptors that regulate LFA-1-dependent adhesion via a putative, Ia-coupled protein kinase(s).

Adhesion molecules on endothelial cells in the central nervous system: an emerging area in the neuroimmunology of multiple sclerosis

The observation of lymphocyte adhesion/homing molecules with ligands (integrins and vascular addressins) on endothelial cells (EC) within target organs during a number of nonlymphoid chronic inflammatory conditions is occurring with increasing frequency. On the basis of evidence from the literature and pilot data on the localization of the putative vascular addressin for humans, HECA-452, in central nervous system (CNS) tissue, it is suggested that molecular recognition on CNS EC might play a pathogenetic role during immune-mediated demyelination in multiple sclerosis (MS). In one of six cases of MS, a case displaying a particularly malignant course, HECA-452 was specifically and reproducibly demonstrated on postcapillary venules in periplaque white matter beyond the zone of active inflammation. In the same case, CD8+ T cells predominated over CD4+ cells. In no case studied were EC positive for HLA-DR (Ia), in contrast to previous reports. Perivascular Ia positivity was common and was always associated with foamy macrophages or pericytes. In view of the occurrence of semiorganized lymphoid collections in a number of chronic inflammatory conditions, several of which are associated with expression of HEV markers, and in MS, it is concluded that examination of molecular recognition events on lymphocytes and EC within the CNS in MS is an area worthy of further study and an area with considerable therapeutic import.

Cognate interactions between helper T cells and B cells

The mechanism by which mammals produce an antibody response after exposure to antigen has intrigued biologists for over a hundred years. Here, Randolph Noelle and Charles Snow review some of the experimental findings since the early 1970s that have advanced understanding of the mechanisms operating during B-cell activation by thymus-dependent (TD) antigens. They also propose a model for B-cell activation that emphasizes the critical role played by direct cellular interactions between B cells and helper T(TH) cells and seek to place into perspective the role played by the membrane immunoglobulin (mlg) receptor in cognate responses.

Expression of the Epstein-Barr virus (EBV)-encoded membrane antigen (LMP) increases the stimulatory capacity of EBV-negative B lymphoma lines in allogeneic mixed lymphocyte cultures

Epstein-Barr virus (EBV)-negative Burkitt lymphoma (BL) lines are poor stimulators in allogeneic mixed lymphocyte cultures compared to EBV-transformed lymphoblastoid cell lines derived from the same individuals. We have previously shown that the stimulatory capacity of the tumor cells is increased after EBV conversion (Avila-Carino et al., Int. J. Cancer 1987. 40: 691). As a first step towards the identification of the viral gene product responsible for this change we have studied the influence of the EBV latent membrane protein (LMP) on the stimulatory capacity of the EBV-negative BL lines BL41 and DG75 and the B lymphoma line BJAB. Four LMP-transfected sublines of BL41, four DG75 LMP transfectants and one LMP-transfected subline of BJAB showed a significantly stronger stimulatory capacity than the original line. The effect was directly proportional to the amount of LMP detected in each transfectant but was not due to reactivation of LMP-specific memory cells since lymphocytes from EBV-seropositive and -seronegative individuals responded equally. In order to define the relation between LMP expression and induction of stimulatory capacity, DG75 was transfected with constructs containing the LMP gene under the control of an heat-shock promoter. The peak of LMP expression in heat shock-treated cells preceded the appearance of stimulatory capacity by 6-12 h suggesting that critical amounts of the protein may be required to induce the phenotypic change recognized by the T cells. LMP influenced in a dose-dependent manner the expression of the adhesion molecules LFA-1, LFA-3 and ICAM-1 and B cell activation markers CD23 and CD39 in transfected sublines of BL41, but did not affect the expression of these markers in the DG75 and BJAB cell line. All LMP-expressing transfectants showed an increased capacity to form conjugates with unprimed allogeneic lymphocytes.

T-T cell interactions are mediated by adhesion molecules

The mechanism by which T cells signal other T cells is not well defined. This was investigated by studying the ability of circulating T cells to induce the proliferation of autologous T cell clones. Peripheral blood T cells activated by cross-linking of the CD3/T cell receptor complex, which increased the expression of cell adhesion molecules LFA-1, LFA-3 and ICAM-1, induced the proliferation of autologous T cell clones. Irradiated antigen-activated peripheral blood T cells could also induce the proliferation of T cell clones which could not recognize that antigen. T-T cell activation required cell contact, was not major histocompatibility complex (MHC) restricted and was blocked by monoclonal antibodies directed against adhesion molecules CD2 and LFA-3 but was not blocked by antibody to class II MHC determinants. As CD2 is the natural ligand for LFA-3, increased expression of T cell surface adhesion molecules LFA-1, ICAM-1 and particularly LFA-3 during an inflammatory response may rapidly recruit T cells that are activated through the CD2 pathway. These results allow a simplified model to explain how relatively few antigen/MHC-specific T cells can recruit large numbers of non-antigen-specific T cells in the generation of an inflammatory response and postulates a novel role of the CD2 molecule in T cell immune function.

Two-way signalling through the LFA-1 lymphocyte adhesion receptor

T lymphocyte recognition of foreign antigens and migration throughout the body require the regulated adhesion of lymphocytes to diverse types of cells and to the extracellular matrix. The lymphocyte adhesion 'receptor' LFA-1, a member of the integrin family, interacts with ICAM-1 and other counter-receptors to mediate adhesion. The LFA-1/ICAM-1 interaction is regulated by signals transmitted from the cytoplasm to the extracellular space. Conversely, LFA-1 transmits signals from the extracellular space to the cytoplasm to regulate T lymphocyte activation. The observed properties of LFA-1 and related adhesion 'receptors' are incorporated into a general model for adhesion during immune surveillance and recognition of foreign antigens.

Interactions between lymphocytes and dermal fibroblasts: an in vitro model of cutaneous lymphocyte trafficking

Cultures of dermal fibroblasts were established from skin biopsies of CBA mice and used to study the interactions with murine T-lymphocytes. Electron microscopy showed that zones of contact developed between the fibroblasts and the T-cells, particularly after mitogenic activation. The adhesion of the lymphocytes was temperature-dependent, and many more lymphoblasts than resting cells attached to the fibroblast monolayers. Flow cytometry analysis of the adherent population showed that the most prominent type of resting lymphocyte was of the CD4 phenotype, which was also observed using a T-helper lymphoid cell line. However, neither the CD4 nor the CD8 (T-cytotoxic) antigens were involved in the binding process, and while the fibroblasts expressed Class I MHC molecules (but not Class II), these also had no role in mediating lymphocyte adhesion. Although the fibroblasts did not express the ligand Mala-2, the murine homologue of human ICAM-1, a monoclonal antibody against LFA-1, its cognate receptor on the lymphocytes, nevertheless effectively inhibited binding. T-cell attachment was also partially prevented by antibody against the lymphocyte CD2 antigen and by RGDS, a protein epitope known to mediate a number of receptor-integrin interactions. Moreover, this peptide also rapidly and preferentially detached T-lymphocytes which had previously adhered to the fibroblast monolayers. Lymphocyte binding was substantially elevated following treatment of the fibroblasts with cytokines such as tumor necrosis factor-alpha and interferon-gamma, but not interleukin-1 alpha. This increase in adhesiveness was, however, almost completely abolished by monoclonal antibodies specific for LFA-1 or for Mala-2. The results of this study show that while lymphocytes recognize fibroblasts normally via a number of constitutively expressed receptor-integrin interactions, their adhesion can also be modulated by cytokine-induced changes in the expression of other surface ligands.

Stimulation of cloned human T lymphocytes via the CD3 or CD28 molecules induces enhancement in vascular endothelial permeability to macromolecules with participation of type-1 and type-2 intercellular adhesion pathways

Perivascular accumulation of CD29+CD45R0+ memory T lymphocytes at sites of chronic inflammation such as rheumatoid synovium is commonly associated with the localized increase in the endothelial permeability. We have recently demonstrated that a direct interaction between activated CD29+CD45R0+ memory T lymphocytes and vascular endothelial cells (EC) results in the increased permeability of EC. In this report, we have investigated effects on antigen-specific T cell receptor (TcR) alpha/beta+ human T lymphocyte clones on the endothelial permeability to albumin. Our results show that CD29+CD45R0+ cloned human T lymphocytes augment endothelial permeability by a noncytolytic process requiring surface contact between T lymphocytes and EC. Both cytolytic and noncytolytic cloned T lymphocytes were capable of augmenting endothelial permeability and this process did not involve active lysis of EC. Stimulation of T lymphocytes via the CD3/TcR or CD28 molecules resulted in significant enhancement in the ability of T lymphocytes to influence endothelial permeability. Pretreatment of T lymphocytes with monoclonal antibodies directed at either CD11a/CD18 (LFA-1) or CD2 molecules or that of EC with monoclonal antibodies directed at either CD54 (ICAM-1) or CD58 (LFA-3) molecules significantly inhibited T lymphocyte-induced enhancement in endothelial permeability, thus indicating that activated T lymphocytes utilize both type-1 (CD11a/CD18CD54) and type-2 (CD2CD58) intercellular adhesion pathways to augment endothelial permeability and signals received via CD3 or CD28 molecules on T lymphocytes further enhance this process. Furthermore, proinflammatory cytokines interleukin 1 and tumor necrosis factor but not proinflammatory cytokines interleukin 1 and tumor necrosis factor but not interleukin 6 induced resistance in EC to T lymphocyte-mediated effects on their permeability. Collectively, these observations may provide insights into molecular mechanism(s) underlying pathophysiology of localized chronic inflammatory responses in general and more specifically selective accumulation of chronically activated memory T lymphocytes at sites of chronic inflammation.

Adhesion of human B cells to germinal centers in vitro involves VLA-4 and INCAM-110

Human B lymphocytes localize and differentiate within the microenvironment of lymphoid germinal centers. A frozen section binding assay was developed for the identification of those molecules involved in the adhesive interactions between B cells and lymphoid follicles. Activated human B cells and B cell lines were found to selectively adhere to germinal centers. The VLA-4 molecule on the lymphocyte and the adhesion molecule INCAM-110, expressed on follicular dendritic cells, supported this interaction. This cellular interaction model can be used for the study of how B cells differentiate.

Adhesion receptors of the immune system

The adhesive interactions of cells with other cells and with the extracellular matrix are crucial to all developmental processes, but have a central role in the functions of the immune system throughout life. Three families of cell-surface molecules regulate the migration of lymphocytes and the interactions of activated cells during immune responses.

Recognition of keratinocytes by cytotoxic T cells specific for conventional HLA class-I alloantigen

This study analyzed whether human keratinocytes (KC) express conventional HLA class-I molecules as detected by class-I-specific cytotoxic T lymphocytes (CTL), and whether exposure of KC to interferon-gamma (IFN-g) is required for CTL recognition. Basal KC grown in serum-free medium and exposed to recombinant IFN-g for 24-96 h were used as targets in 51Cr-release assays. Target-cell susceptibilities to lysis were compared by analyzing the lytic unit (LU) activity of a given CTL population against IFN-g-treated and untreated KC. CTL effectors were cloned from alloantigen-primed cultures by limiting dilution in the presence of antigenic B lymphoblastoid cells (BCLL) and IL-2. These T-cell clones lysed appropriate BCLL and PHA blasts but not third-party BCLL or K562. Lysis of antigenic BCLL was specifically blocked by antibodies against CD3 or class-I antigens. Specificity of the clones for conventional class-I antigen was demonstrated by cytotoxicity tests employing a panel of HLA-typed BCLL. The clones specifically lysed KC syngeneic with the original effector immunogen, and lysis was also blocked by anti-class-I antibodies. The effect of IFN-g treatment was to increase KC susceptibility to lysis by these clones. From 3-25 times more LU were measured against IFN-g-treated KC than against nontreated KC, and the degree of enhancement was similar for KC treated with concentrations of IFN-g ranging from 2.5-200 U/ml. This effect of IFN-g treatment on KC lysis by CTL, which was detected after only 24 h at all doses tested, emphasizes the potential role of IFN-g in enhancing CTL-mediated antiviral epidermal immunity and in exacerbating epidermal disease mediated by specific lytic T cells. In addition, the finding that normal human KC can be recognized by MHC class-I-specific CTL demonstrates that KC do express conventional class-I-antigens and that KC lysis by CTL can occur independently of exogenous cytokines.

Activated CD8 binding to class I protein mediated by the T-cell receptor results in signalling

The CD8 glycoprotein of T cells bind nonpolymorphic regions of class I major histocompatibility complex proteins on target cells and these interactions promote antigen recognition and signalling by the T-cell receptor. Studies using artificial membranes indicated that effective CD8/class I interaction is critical for response by alloantigen-specific cytotoxic T lymphocytes when class I protein is the only ligand on the antigen-bearing surface. But significant CD8-mediated binding of cytotoxic T lymphocytes to non-antigenic class I protein could not be detected in the absence of the alloantigen. These apparently contradictory findings indicate that CD8 binding to class I protein might be activated through the T-cell receptor and the results reported here demonstrate that this is the case. Treatment of cytotoxic T lymphocytes with soluble anti-T-cell receptor antibody activates adhesion of the cytotoxic T lymphocytes to class I, but not class II proteins. The specificity of this binding implies that it is mediated by CD8 and blocking by anti-CD8 antibodies confirmed this. Furthermore, binding of CD8 to class I protein resulted in generation of an additional signal(s) necessary to initiate response at low T-cell receptor occupancy levels.

Cytokine regulation of intercellular adhesion molecule-1 (ICAM-1) expression on human glioblastoma cells

Intercellular adhesion molecule-1 (ICAM-1) has recently been identified as one of the ligands for lymphocyte function-associated antigen-1 (LFA-1). Immunohistochemical staining of frozen tissue sections using the ICAM-1 antibody RR1/1 demonstrated significant levels of ICAM-1 expression on human glioblastoma cells and on intratumoural vascular endothelial cells. ICAM-1 was weakly expressed or absent from low grade gliomas and absent from normal and fetal brain. ICAM-1 expression was similar to that of MHC class II. HLA-DR antigens. Glioblastoma cell lines constitutively expressed ICAM-1 to a minimal or moderate extent. Surface antigen expression of ICAM-1 and ICAM-1-specific mRNA could be significantly increased by incubating glioblastoma cells with interleukin-1 beta (IL-1 beta), tumour necrosis factor-alpha (TNF-alpha), and interferon-gamma (IFN-gamma). IL-2, IL-4, IL-6 and transforming growth factor beta 2 (TGF-beta 2) had no significant effect on surface antigen expression. Significant enhancement of ICAM-1 expression was obtained using TNF-alpha and IL-1 beta at 1-10 U/ml and at 500 U/ml of IFN-gamma. Induction of ICAM-1 specific mRNA was observed 4 h after cytokine treatment and decreased by 24 h. Surface antigen expression of ICAM-1 increased for up to 48 h after treatment.

Dominance of memory over naive T cells in contact dermatitis is due to differential tissue immigration

CD4+ T cells include a naive (CD4-, CD45RO-, CD29-, CD45RA+) as well as a memory subpopulation (CD4+, CD45RO+, CD29+, CD45RA-). These subpopulations represent different stages in T-cell development and function. Recently, it has been shown that inflammatory and neoplastic CD4+ T-cell infiltrates are dominated by the memory subpopulation, whereas both subpopulations are about the same size in the peripheral blood. This was thought to be the result of in situ maturation of naive into memory T cells. We analysed early positive patch-test reactions 1-2 days after antigen challenge and found that most of the CD4+ T cells that had freshly immigrated into the tissue carried the memory phenotype. Their preferential migration may be mediated by at least five adhesion molecules expressed on their cell surface. This observation has important pathogenetic implications, since memory T cells can be rapidly activated by antigens and secrete a wide variety of pro-inflammatory cytokines.

The role of the type 3 complement receptor in the induced recruitment of myelomonocytic cells to inflammatory sites in the mouse

The type 3 complement receptor (CR3), initially identified as the leukocyte cell surface receptor for iC3b, is now known to form part of the extended integrin family of cell adhesion molecules that mediate both cell-cell and cell-extracellular matrix interactions. The identification of a heritable deficiency of human leukocyte adhesion together with the advent of monoclonal antibodies has shed some light on the central role of CR3 in the transendothelial migration of macrophages and neutrophils to sites of inflammation. We review the general structural features of CR3 and then examine our understanding of its role in both nonspecific and T cell-dependent inflammatory processes based on our murine in vivo experiments. CR3-dependent inflammation seems to contribute to the pulmonary response to some stimuli (lipopolysaccharide) but not to others (bacillus Calmette-Guerin). These studies highlight the potential therapeutic benefits, as well as the significant risks of potentiating acute bacterial infections, of CR3 blockade in vivo.

Distinct mutations in two patients with leukocyte adhesion deficiency and their functional correlates

Two patients with leukocyte adhesion deficiency (LAD), one with a moderate phenotype (patient 14) and one with a severe phenotype (patient 2) who had been shown to have a normal sized beta subunit protein precursor, were analyzed in an attempt to determine the molecular basis for their disease. RNase mapping located possible mutations to two distinct but adjacent regions of the beta subunit cDNA. Sequencing of patient-derived cDNA clones in this region revealed a C for T difference at amino acid 149 in patient 14 which resulted in the substitution of a leucine for a proline, and an A for G substitution at amino acid 169 in patient 2 which mutated a glycine to an arginine. The mutated amino acids are in a region of the cDNA that is highly conserved between the beta subunits of the integrin family and are identical in all known integrin beta subunits. Co-transfection of the beta subunit cDNA containing the patient 2 mutation with the wild-type alpha subunit of LFA-1 in a mammalian expression system resulted in no expression of LFA-1. In the case of the mutation in patient 14 there was markedly diminished expression of LFA-1 with loss of function and loss of the epitope for a number of anti-beta mAbs. Normal half-life of the mutant beta subunits, and previous demonstration of a lack of alpha/beta complex formation during biosynthesis in patient cells, suggest a defect in association with the alpha subunit. Association with beta is required for expression of the alpha subunit of LFA-1. Loss of functional expression with both of these beta subunit mutations suggests that they lie in a site critical for association with the alpha subunit.

Correction of CD18-deficient lymphocytes by retrovirus-mediated gene transfer

Leukocyte adhesion deficiency (LAD) is an inherited disorder of leukocyte function caused by derangements in CD18 expression. The genetic and functional abnormalities in a lymphocyte cell line from a patient with LAD have been corrected by retrovirus-mediated transduction of a functional CD18 gene. Lymphocytes from patients with LAD were exposed to CD18-expressing retrovirus and enriched for cells that express CD11a and CD18 (LFA-1) on the cell surface. Molecular and functional analyses of these cells revealed (i) one copy of proviral sequence per cell, (ii) viral-directed CD18 RNA that exceeded normal endogenous levels, (iii) normal quantities of CD11a and CD18 protein on the cell surface, and (iv) reconstitution of LFA-1-dependent adhesive function.

Characterization and functional analysis of interferon-gamma-induced intercellular adhesion molecule-1 expression in human keratinocytes and A-431 cells

Human intercellular adhesion molecule-1 (ICAM-1) is a cell-surface glycoprotein that serves as one of the major ligands for lymphocyte function-associated antigen-1 (LFA-1), a member of the integrin supergene family of adhesion molecules that is involved in cell-cell adhesion. Homotypic and heterotypic conjugate formation between leukocytes and between leukocytes and target cells via the LFA-1/ICAM-1 interaction has been demonstrated to be a critical event in numerous immunologic and inflammatory processes. While LFA-1 is expressed by all leukocytes, ICAM-1 is not normally expressed by all tissues with which leukocytes interact, but ICAM-1 may be induced de novo by various cytokines, including interferon-gamma (IFN-gamma). The constitutive and IFN-gamma-induced expression and function of ICAM-1 in human keratinocytes (HK) and A-431 cells in culture has been analyzed. While A-431 cells constitutively express ICAM-1 when assessed by northern blotting, by biosynthetic labeling and immunoprecipitation, and by flow cytometry, HK do not. When these two cell types are exposed to recombinant human (rh-) IFN-gamma at 1000 U/ml for 24 h, A-431 cells upregulate ICAM-1 and HK express ICAM-1 to an equal degree when assessed by these same parameters. Furthermore, in an in vitro adhesion assay, rh-IFN-gamma treatment of the HK or A-431 cells greatly increases the specific adherence of radiolabeled T cells to these cells. These data provide further evidence for the potential role of the regulated expression of ICAM-1 by keratinocytes in immunologic and inflammatory responses occurring in the skin.

An alternative leukocyte homotypic adhesion mechanism, LFA-1/ICAM-1-independent, triggered through the human VLA-4 integrin

The VLA-4 (CD49d/CD29) integrin is the only member of the VLA family expressed by resting lymphoid cells that has been involved in cell-cell adhesive interactions. We here describe the triggering of homotypic cell aggregation of peripheral blood T lymphocytes and myelomonocytic cells by mAbs specific for certain epitopes of the human VLA alpha 4 subunit. This anti-VLA-4-induced cell adhesion is isotype and Fc independent. Similar to phorbol ester-induced homotypic adhesion, cell aggregation triggered through VLA-4 requires the presence of divalent cations, integrity of cytoskeleton and active metabolism. However, both adhesion phenomena differed at their kinetics and temperature requirements. Moreover, cell adhesion triggered through VLA-4 cannot be inhibited by cell preincubation with anti-LFA-1 alpha (CD11a), LFA-1 beta (CD18), or ICAM-1 (CD54) mAb as opposed to that mediated by phorbol esters, indicating that it is a LFA-1/ICAM-1 independent process. Antibodies specific for CD2 or LFA-3 (CD58) did not affect the VLA-4-mediated cell adhesion. The ability to inhibit this aggregation by other anti-VLA-4-specific antibodies recognizing epitopes on either the VLA alpha 4 (CD49d) or beta (CD29) chains suggests that VLA-4 is directly involved in the adhesion process. Furthermore, the simultaneous binding of a pair of aggregation-inducing mAbs specific for distinct antigenic sites on the alpha 4 chain resulted in the abrogation of cell aggregation. These results indicate that VLA-4-mediated aggregation may constitute a novel leukocyte adhesion pathway.

Expression of intercellular adhesion molecule-1 (ICAM-1) on human thyroid cells lines correlated with their binding of lymphoblasts

We have investigated the expression of intercellular adhesion molecule-1 (ICAM-1) by novel functional human thyroid cell lines (designated SGHTL). ICAM-1 is constitutively expressed and it is rapidly upregulated in response to each of the recombinant cytokines: gamma-interferon, interleukin-1 and tumour necrosis factor. This contrasts with the more slowly increased expression of major histocompatibility complex (MHC) class II antigens in response to gamma-interferon alone. We have also demonstrated binding of activated lymphocytes to SGHTL cells: this interaction is increased following treatment with these cytokines and is inhibited by monoclonal antibodies directed against ICAM-1 or lymphocyte function-associated antigen-1 (LFA-1) but not by antibodies against CD2 or MHC class II antigens. Hence, we conclude that the binding of lymphoblasts to human thyroid cells involves an LFA-1- and ICAM-1-dependent pathway as well as other basal and cytokine-inducible pathway(s). These do not appear to involve MHC class II antigens, CD2 or an LFA-1 ligand other than ICAM-1.

Regulated expression and binding of three VLA (beta 1) integrin receptors on T cells

Regulated adhesion of T cells to extracellular matrix (ECM) proteins is likely to be essential in T cell migration. Constitutive binding of various other cell types to ECM components is mediated by members of the VLA (very late antigen) subfamily of integrins. We describe here the regulated binding of resting CD4+ human T cells to ECM through three VLA integrins: VLA-4 and VLA-5 binding to fibronectin (FN), and a novel pathway of VLA-6 binding to laminin (LN). Binding to ECM is regulated in two ways. First, unlike other VLA-mediated interactions, VLA binding activity of the T cells is rapidly and dramatically augmented with cell activation without change in level of expression of the VLA molecules. Second, binding is regulated with T-cell differentiation; memory T cells express three- to four-fold more VLA-4, VLA-5, and VLA-6 than do naive cells, and bind more efficiently through them to FN and LN.

Epstein-Barr virus latent membrane protein (LMP1) and nuclear proteins 2 and 3C are effectors of phenotypic changes in B lymphocytes: EBNA-2 and LMP1 cooperatively induce CD23

Latent Epstein-Barr virus (EBV) infection and growth transformation of B lymphocytes is characterized by EBV nuclear and membrane protein expression (EBV nuclear antigen [EBNA] and latent membrane protein [LMP], respectively). LMP1 is known to be an oncogene in rodent fibroblasts and to induce B-lymphocyte activation and cellular adhesion molecules in the EBV-negative Burkitt's lymphoma cell line Louckes. EBNA-2 is required for EBV-induced growth transformation; it lowers rodent fibroblast serum dependence and specifically induces the B-lymphocyte activation antigen CD23 in Louckes cells. These initial observations are now extended through an expanded study of EBNA- and LMP1-induced phenotypic effects in a different EBV-negative B-lymphoma cell line, BJAB. LMP1 effects were also evaluated in the EBV-negative B-lymphoma cell line BL41 and the EBV-positive Burkitt's lymphoma cell line, Daudi (Daudi is deleted for EBNA-2 and does not express LMP). Previously described EBNA-2- and LMP1-transfected Louckes cells were studied in parallel. EBNA-2, from EBV-1 strains but not EBV-2, induced CD23 and CD21 expression in transfected BJAB cells. In contrast, EBNA-3C induced CD21 but not CD23, while no changes were evident in vector control-, EBNA-1-, or EBNA-LP-transfected clones. EBNAs did not affect CD10, CD30, CD39, CD40, CD44, or cellular adhesion molecules. LMP1 expression in all cell lines induced growth in large clumps and expression of the cellular adhesion molecules ICAM-1, LFA-1, and LFA-3 in those cell lines which constitutively express low levels. LMP1 expression induced marked homotypic adhesion in the BJAB cell line, despite the fact that there was no significant increase in the high constitutive BJAB LFA-1 and ICAM-1 levels, suggesting that LMP1 also induces an associated functional change in these molecules. LMP1 induction of these cellular adhesion molecules was also associated with increased heterotypic adhesion to T lymphocytes. The Burkitt's lymphoma marker, CALLA (CD10), was uniformly down regulated by LMP1 in all cell lines. In contrast, LMP1 induced unique profiles of B-lymphocyte activation antigens in the various cell lines. LMP1 induced CD23 and CD39 in BJAB; CD23 in Louckes; CD39 and CD40 in BL41; and CD21, CD40, and CD44 in Daudi. In BJAB, CD23 surface and mRNA expression were markedly increased by EBNA-2 and LMP1 coexpression, compared with EBNA-2 or LMP1 alone. This cooperative effect was CD23 specific, since no such effect was observed on another marker, CD21.(ABSTRACT TRUNCATED AT 400 WORDS)

Gamma/delta T cell clones and natural killer cell clones mediate distinct patterns of non-major histocompatibility complex-restricted cytolysis

Non-MHC-restricted killer cells are cytotoxic lymphocytes that can mediate cytolysis of most tumor targets without apparent selectivity and restriction by the MHC, particularly when activated with IL-2. These effector cells include predominantly NK cells and T cells expressing the TCR-gamma/delta. We found that TCR-gamma/delta-1+, delta TSC1-, BB3+, Ti gamma A+ T cell clones mediate a characteristic cytolytic pattern of non-MHC-restricted cytolysis that is markedly different from NK clones and alpha/beta T cell clones derived from the peripheral blood of the same normal individuals. The characteristic finding is that all BB3/Ti gamma A+ gamma/delta clones mediate strong cytolysis of Daudi cells but they do not lyse Raji cells. In contrast, NK clones from the same donors mediate strong cytolysis of both Daudi and Raji targets. Cytotoxicity by the gamma/delta clones on certain target cells such as Daudi and Molt 4 can be specifically inhibited by mAbs reactive against the TCR-gamma/delta. Therefore, the TCR-gamma/delta on these clones either directly recognizes target epitopes on some tumor targets or it is involved in the regulation of their cytotoxic function. The expression of TCR-gamma/delta products reacting with the BB3 and Ti gamma A mAbs reflects the usage of identical TCR-gamma/delta V region genes that appear to be associated with the characteristic pattern of non-MHC-restricted cytotoxicity displayed by this major subset of human peripheral blood gamma/delta cells.

The arrangement of the immunoglobulin-like domains of ICAM-1 and the binding sites for LFA-1 and rhinovirus

Intercellular adhesion molecule 1 (ICAM-1, CD54) binds to the integrin LFA-1 (CD11a/CD18), promoting cell adhesion in immune and inflammatory reactions. ICAM-1 is also subverted as a receptor by the major group of rhinoviruses. Electron micrographs show that ICAM-1 is a bent rod, 18.7 nm long, suggesting a model in which the five immunoglobulin-like domains are oriented head to tail at a small angle to the rod axis. ICAM-1 sequences important to binding LFA-1, rhinovirus, and four monoclonal antibodies were identified through the characterization of chimeric ICAM-1 molecules and mutants. The amino-terminal two immunoglobulin-like domains of ICAM-1 appear to interact conformationally. Domain 1 of ICAM-1 contains the primary site of contact for both LFA-1 and rhinovirus; the presence of domains 3-5 markedly affects the accessibility of the binding site for rhinovirus and less so for LFA-1. The binding sites appear to be distinct but overlapping; rhinovirus binding also differs from LFA-1 binding in its lack of divalent cation dependence. Our analysis suggests that rhinoviruses mimic LFA-1 in binding to the most membrane-distal, and thus most accessible, site of ICAM-1.

Leukocyte-cell adhesion: a molecular process fundamental in leukocyte physiology

Leukocyte-cell adhesion is a form of physical contact characterized by fast (firm) stickiness between the cells. To analyze the biology and molecular basis of this process, an adhesion-specific assay was developed: the phorbol ester-induced aggregation of human lymphocytes. This rapid and antigen-independent intercellular adhesion requires cellular metabolism, an intact cytoskeleton and extracellular divalent cations, and is mediated by preformed cell-surface proteins referred to as CAMs. Phorbol ester also induces aggregation of monocytes and granulocytes, as well as adhesion of T lymphocytes to either B cells or monocytes and of the leukocytes to vascular endothelial cells. By using the adhesion-specific assay and blocking monoclonal antibodies, several CAMs have been identified, namely the Leu-CAM family (CD11a-c/CD18) and ICAM-1 (CD54). The Leu-CAM family is composed of Leu-CAMa (CD11a/CD18), Leu-CAMb (CD11b/CD18) and Leu-CAMc (CD11c/CD18), three glycoprotein heterodimers made of a common beta-chain and distinct alpha-chains. ICAM-1 is an adhesive ligand for Leu-CAMa. Expression and use of the various CAMs is selective in different types of leukocytes. The Leu-CAMs have been purified and partially characterized. CD18, whose gene is on human chromosome 21, contains 5-6 N-linked complex-type oligosaccharides, and CD11 binds Ca++. Another adhesion pathway is mediated by CD2 and CD58. CD2, a glycoprotein selectively expressed by T cells, is a receptor for CD58, a cell-surface adhesive ligand with broad tissue distribution. Antibodies to the latter CAMs do not block the phorbol ester-induced lymphocyte aggregation. Adhesion is involved in a large variety of leukocyte functions. Anti-Leu-CAM antibodies block induction of IL-2 production and lymphocyte proliferation. Lymphocyte-mediated cytotoxicity is also inhibited. Endogenous NK and LAK cells use Leu-CAMs, ICAM-1 and CD2, and sometimes RGD receptors, to bind and kill tumor cells. Endogenous compounds such as H2O2 and LTB4 also induce Leu-CAM-dependent adhesion in monocytoid cells and granulocytes, respectively, and degranulation of the latter cells is enhanced by the adhesion process. Homologous CAMs have been identified in rabbit and mouse. In in vivo studies in the former species, anti-Leu-CAM antibodies block adhesion of leukocytes to vascular endothelium and thereby their migration into extravascular tissues. The antibodies thus inhibit granulocyte accumulation and plasma leakage in inflammatory lesions, and induce lympho- and granulocytosis, indicating that cell-adhesion contributes to the distribution of leukocytes in the body.(ABSTRACT TRUNCATED AT 400 WORDS)

Roles of adhesion molecules in T-cell recognition: fundamental similarities between four integrins on resting human T cells (LFA-1, VLA-4, VLA-5, VLA-6) in expression, binding, and costimulation

This review summarizes our recent work on expression and function of 4 integrins on resting human CD4+ T cells. Three themes are highlighted: multiplicity of molecular pathways of adhesion, regulation of adhesion, and costimulation by adhesion molecules. Four distinct receptor/ligand interactions have been elucidated: LFA-1/ICAM-1, VLA-5/fibronection, VLA-4/fibronectin, and VLA-6/laminin. Our studies indicate fundamental similarities in function and regulation of these four receptor/ligand interactions: 1) acute activation of the T cell (by CD3/TCR crosslinking or by PMA) induces rapid but transient integrin binding function; and 2) higher expression of each integrin on memory T cells compared to naive T cells results in greater binding of memory cells to each ligand. The identification of T-cell integrins (VLA-4, VLA-5, VLA-6) which interact with ECM components directs attention to the potential importance of T-cell interactions with ECM components which either may be immobilized in ECM or which may act as molecular bridges between cells. The existence of multiple adhesion pathways, of multiple ligands for a single receptor (such as LFA-1/ICAM-1 and LFA-1/ICAM-2), multiple receptors for a single ligand (such as VLA-4/FN and VLA-5/FN), and regulation of ligand expression (ICAM-1) provides opportunities for co-operativity, rebundancy and diversity which the T cell utilizes to exquisitely regulate its adhesive interactions. The thesis that adhesion molecules can be multifunctional receptors that also influence signalling is demonstrated by our findings that each of these integrin receptor/ligand interactions is capable of providing a potent costimulatory signal to CD3-mediated T-cell activation. The importance of interactions of T-cell integrins with their cell surface and ECM ligands is discussed with respect to T-cell migration, differentiation and recognition. Analysis of the precise mechanisms by which T cells regulate and exploit these multiple receptor/ligand interactions and the resulting functional consequences of those interactions will be exciting areas of future research.

EndoCAM: a novel endothelial cell-cell adhesion molecule

Cell-cell adhesion is controlled by many molecules found on the cell surface. In addition to the constituents of well-defined junctional structures, there are the molecules that are thought to play a role in the initial interactions of cells and that appear at precise times during development. These include the cadherins and cell adhesion molecules (CAMs). Representatives of these families of adhesion molecules have been isolated from most of the major tissues. The notable exception is the vascular endothelium. Here we report the identification of a cell surface molecule designated "endoCAM" (endothelial Cell Adhesion Molecule), which may function as an endothelial cell-cell adhesion molecule. EndoCAM is a 130-kD glycoprotein expressed on the surface of endothelial cells both in culture and in situ. It is localized to the borders of contiguous endothelial cells. It is also present on platelets and white blood cells. Antibodies against endoCAM prevent the initial formation of endothelial cell-cell contacts. Despite similarities in size and intercellular location, endoCAM does not appear to be a member of the cadherin family of adhesion receptors. The serologic and protease susceptibility characteristics of endoCAM are different from those of the known cadherins, including an endogenous endothelial cadherin. Although the precise biologic function of endoCAM has not been determined, it appears to be one of the molecules responsible for regulating endothelial cell-cell adhesion processes and may be involved in platelet and white blood cell interactions with the endothelium.

Biological activities of a synthetic peptide composed of two unlinked domains from a retroviral transmembrane protein sequence

We report several biological activities of a synthetic peptide whose sequence contains the highly conserved region of feline leukemia virus transmembrane protein (TM) synthetically linked to another short TM-derived sequence particularly rich in polar positive residues. This 29-amino-acid peptide blocked [3H]thymidine uptake 30 to 50% by concanavalin A-stimulated CD4(+)--but not CD8(+)-enriched murine splenocytes. Maximal suppression was detected at 12.5 micrograms (3 microM) to 75 micrograms (19 microM) per ml of growth medium; stimulation of [3H]thymidine uptake was observed at higher peptide concentrations. The synthetic peptide inhibited but did not stimulate [3H]thymidine uptake by mitogen-activated thymocytes and antibody production by splenocytes as determined in a liquid hemolytic plaque assay. Similarities are reported between a consensus sequence of diverse retroviral TMs and a region of alpha interferons shown by others to be important for antiviral and cytostatic properties. The TM sequence-derived synthetic peptide blocked in a nontoxic and sequence-specific manner the release of murine leukemia virus from two chronically infected cell lines. We suggest that some of the biological effects of retroviral TM are mediated through a common pathway shared with alpha interferons.

Transfection of cells from patients with leukocyte adhesion deficiency with an integrin beta subunit (CD18) restores lymphocyte function-associated antigen-1 expression and function

Leukocyte adhesion deficiency (LAD) is an inherited immunodeficiency disease that is characterized by the deficient expression of the leukocyte adhesion glycoproteins lymphocyte function-associated antigen-1 (LFA-1), Mac-1, and p150,95. This loss of expression is attributed to heterogeneous defects in the common beta subunit shared by these glycoproteins. Here we demonstrate that expression of the LFA-1 alpha beta heterodimer in EBV-transformed B lymphoblastoid cells from LAD patients can be recovered after transfection with the beta subunit cDNA contained in an EBV-based vector. Four patients with differing severities of LAD comprising three distinct classes of mutations were studied. Flow cytometry analysis of stably transfected patient cells revealed near normal levels of expression of both the alpha and beta chains of LFA-1, and immunoprecipitation studies confirmed that fully processed alpha and beta chains were being expressed at the cell surface. In addition, Northern analysis of mRNA expression also demonstrated that the transfected LAD patient cells were expressing high quantities of exogenous beta subunit mRNA. Functional studies such as homotypic adhesion and adhesion to a purified counterreceptor for LFA-1, intracellular adhesion molecule-1, demonstrated that LFA-1 function had been restored in the stably transfected LAD patient cell lines. These studies unequivocally show that the defect in cells from patients with LAD is in the leukocyte integrin beta subunit.

A signaling role for the cytoplasmic segment of the CD8 alpha chain detected under limiting stimulatory conditions

To test for the functional importance of the cytoplasmic segment of the CD8 molecule, a mouse T-cell hybridoma expressing a T-cell receptor specific for the class I major histocompatibility complex product H-2Kb was transfected with a set of CD8 alpha-chain (Ly-2) and/or beta-chain (Ly-3) genes encoding polypeptides with carboxyl-terminal truncations or substitutions. When challenged with Kb-positive splenocytes, transfectants expressing Ly-2 homodimers that lacked cytoplasmic tails responded nearly as effectively as wild-type Ly-2 transfectants. However in marked contrast to the wild-type Ly-2 transfectants, tailless Ly-2 transfectants were greatly impaired in their ability to respond to Kb-transfected L cells. Coexpression of the Ly-3 gene did not restore this impaired response. The unique functional property of the Ly-2 alpha cytoplasmic segment was further supported by the analysis of a chimeric Ly-3 subunit in which the cytoplasmic segment was replaced by the one from the Ly-2 alpha subunit. When associated with a soluble Ly-2 subunit lacking a transmembrane segment, the chimeric Ly-3 was indeed sufficient to restore the response to Kb-transfected L cells. Since the lateral mobility of the tailless Ly-2 molecules on the cell surface was nearly identical to that of the wild-type Ly-2 molecules, their partially impaired function may indicate that they have lost their cis-acting signaling properties but retained their ability to bind class I products of the major histocompatibility complex.

The leukocyte integrin LFA-1 reconstituted by cDNA transfection in a nonhematopoietic cell line is functionally active and not transiently regulated

The functional activity of lymphocyte function-associated antigen 1 (LFA-1) on leukocytes can be regulated by T-cell receptor (TCR) stimulation and pharmacologic agents. It was of interest to determine if functionally active LFA-1 could be reconstituted on a nonhematopoietic, LFA-1-negative cell line. We report the expression of LFA-1 and diethylaminoethyl (DEAE) Mac-1 alpha beta heterodimers on the cell surface of a fibroblastoid cell line, COS, by DEAE dextran cotransfection of the alpha and beta subunit cDNAs. Immunoprecipitation studies demonstrated that the alpha and beta subunit was expressed in heterodimers. The alpha or beta subunit was expressed at lower levels after transfection with the alpha or beta subunit cDNA alone. Cotransfection of the alpha and beta subunit cDNAs, but not transfection of alpha or beta alone, was sufficient to reconstitute intercellular adhesion molecule-1 (ICAM-1) binding activity. Consistent with this observation, LFA-1 on the fibroblastoid cells possesses the activation epitope defined by the L16 monoclonal antibody (mAb). This epitope marks the conversion of LFA-1 from the low to high avidity state on peripheral blood T lymphocytes (PBLs) and is constitutively present on activated cell lines. In contrast to LFA-1 on leukocytes, the functional activity of LFA-1 on fibroblastoid cells was not influenced by phorbol ester treatment. Furthermore, the use of agents that interfere with intracellular signaling, a protein kinase C inhibitor, cAMP analogue, or the combination of a phosphodiesterase inhibitor and adenyl cyclase activator, did not affect the binding of COS cells expressing LFA-1 to purified ICAM-1.

VCAM-1 on activated endothelium interacts with the leukocyte integrin VLA-4 at a site distinct from the VLA-4/fibronectin binding site

Cytokine-activated human endothelial cells express vascular cell adhesion molecule-1 (VCAM-1), which binds lymphocytes. We now identify the integrin VLA-4 as a receptor for VCAM-1 because VLA-4 surface expression on K-562 cells (following transfection of the VLA alpha 4 subunit cDNA) resulted in specific cell adhesion to VCAM-1, and anti-VLA-4 antibodies completely inhibited VCAM-1-dependent cell-cell attachment. In addition, VLA-4 expression allowed K-562 cells to attach to the heparin II binding region (FN-40) of fibronectin. However, VLA-4/VCAM-1 and VLA-4/FN-40 interactions are readily distinguishable: only the former was inhibited by the anti-VLA-4 monoclonal antibody HP1/3, and only the latter was inhibited by soluble FN-40. The VCAM-1/VLA-4 ligand-receptor pair may play a major role in the recruitment of mononuclear leukocytes to inflammatory sites in vivo.

Regulation of the local immune response by retinal cells

Experimental autoimmune uveoretinitis (EAU) induced by retinal antigens is a CD4+ (Th) lymphocyte mediated disease. Generation of autoreactive CD4+ cells requires the processing and presentation of autoantigen by antigen presenting cells (APC) in combination with MHC Class II antigen. Efficient presentation of antigen to T cells has also been shown to depend on accessory molecules of adhesion such as intercellular adhesion molecule-1 (ICAM-1) and leukocyte function-associated antigen-1 (LFA-1). Aberrant expression of Class II antigens by local tissue cells has been suggested as a possible mechanism in autoimmune processes. Several ocular cells express Class II antigens during inflammation, while other cells such as Muller cells inhibit antigen presentation in vitro. We have also shown that retinal pigment epithelial cells (constitutively) and endothelial cells (after induction) express ICAM-1 and that CD4+ lymphocyte adhesion to these cells is inhibited by antibodies to ICAM-1. Accessory molecules may therefore be important, not only in local presentation of antigen but in recruitment of circulating autoreactive cells to the eye since these cells represent the site of the blood-retinal barrier. Regulation of the local immune response in the eye therefore, may occur at several levels.

The human integrin VLA-2 is a collagen receptor on some cells and a collagen/laminin receptor on others

The integrin heterodimer VLA-2, previously known as a collagen receptor, is now shown also to be a laminin receptor. Adhesion of the human melanoma cell line LOX to laminin was inhibited by anti-VLA alpha 2 antibodies. Because VLA-2-mediated LOX cell attachment to laminin was not inhibited by digestion with collagenase, collagen contamination of laminin was not a factor. In addition, VLA-2 from LOX cells bound to immobilized laminin, and binding was disrupted by EDTA but not by Arg-Gly-Asp (RGD) peptides. VLA-3 also bound to laminin-Sepharose, although less avidly than VLA-2. Thus, at least four separate members of the integrin beta 1 subfamily serve as laminin receptors--i.e., VLA-2 and VLA-3 (this study) together with VLA-1 and VLA-6 (other reports). Whereas LOX and other cell lines used VLA-2 as both a laminin and collagen receptor, fibroblast VLA-2 mediated collagen but not laminin binding. Likewise, VLA-2 from platelets did not interact with laminin. Despite this functional discordancy, VLA-2 from laminin-binding and nonbinding sources was indistinguishable by all immunochemical and biochemical criteria examined. Thus, functional differences in VLA-2 may be due to cell type-specific modulation.