The vitronectin receptor serves as an accessory molecule for the activation of a subset of gamma/delta T cells

Recognition of synthetic polyanionic ligands underlies "spontaneous" reactivity of Vγ1 γδTCRs

Although γδTCRs were discovered more than 30 yr ago, principles of antigen recognition by these receptors remain unclear and the nature of these antigens is largely elusive. Numerous studies reported that T cell hybridomas expressing several Vγ1-containing TCRs, including the Vγ1Vδ6 TCR of γδNKT cells, spontaneously secrete cytokines. This property was interpreted as recognition of a self-ligand expressed on the hybridoma cells themselves. Here, we revisited this finding using a recently developed reporter system and live single cell imaging. We confirmed strong spontaneous signaling by Vγ1Vδ6 and related TCRs, but not by TCRs from several other γδ or innate-like αβ T cells, and demonstrated that both γ and δ chains contributed to this reactivity. Unexpectedly, live single cell imaging showed that activation of this signaling did not require any interaction between cells. Further investigation revealed that the signaling is instead activated by interaction with negatively charged surfaces abundantly present under regular cell culture conditions and was abrogated when noncharged cell culture vessels were used. This mode of TCR signaling activation was not restricted to the reporter cell lines, as interaction with negatively charged surfaces also triggered TCR signaling in ex vivo Vγ1 γδ T cells. Taken together, these results explain long-standing observations on the spontaneous reactivity of Vγ1Vδ6 TCR and demonstrate an unexpected antigen presentation-independent mode of TCR activation by a spectrum of chemically unrelated polyanionic ligands.

Integral Roles for Integrins in γδ T Cell Function

Integrins are adhesion receptors on the cell surface that enable cells to respond to their environment. Most integrins are heterodimers, comprising α and β type I transmembrane glycoprotein chains with large extracellular domains and short cytoplasmic tails. Integrins deliver signals through multiprotein complexes at the cell surface, which interact with cytoskeletal and signaling proteins to influence gene expression, cell proliferation, morphology, and migration. Integrin expression on γδ T cells (γδTc) has not been systematically investigated; however, reports in the literature dating back to the early 1990s reveal an understated role for integrins in γδTc function. Over the years, integrins have been investigated on resting and/or activated peripheral blood-derived polyclonal γδTc, γδTc clones, as well as γδ T intraepithelial lymphocytes. Differences in integrin expression have been found between αβ T cells (αβTc) and γδTc, as well as between Vδ1 and Vδ2 γδTc. While most studies have focused on human γδTc, research has also been carried out in mouse and bovine models. Roles attributed to γδTc integrins include adhesion, signaling, activation, migration, tissue localization, tissue retention, cell spreading, cytokine secretion, tumor infiltration, and involvement in tumor cell killing. This review attempts to encompass all reports of integrins expressed on γδTc published prior to December 2017, highlights areas warranting further investigation, and discusses the relevance of integrin expression for γδTc function.

Dendritic cell expression of ADAM23 governs T cell proliferation and cytokine production through the α(v)β(3) integrin receptor

ADAM23 is a member of the brain macrophage-derived chemokine family. Structural homology of ADAM proteins suggests their function as integrin receptors. Previous studies have linked ADAM23 as a dominant contributor to brain development and cancer metastasis. The present studies now show that ADAM23 expression on DCs partially governs antigen-presentation capacities to responder CD4⁺ T cells. With the use of RNAi approaches, knockdown of ADAM23 in murine BMDCs resulted in impaired T cell activation, proliferation, and cytokine production. Knockdown did not alter the maturation profile of DCs (i.e., costimulatory molecule expression or production of proinflammatory cytokines) but markedly impaired cognate T cell responses. There was a significant decrease in antigen-specific clonal expansion coupled with a global decrease in Th cytokine production. Impaired early activation and proliferation did not alter/skew the balance of Th polarization but significantly depressed total levels of IL-2, IFN-γ, IL-4, and IL-17 cytokine production in CD4⁺ T cells primed by ADAM23 knockdown versus control DCs. Finally, neutralizing antibodies targeting the α(v)β(3) integrin receptors resulted in similar phenotypes of impaired CD4⁺ T cell responses. Taken together, these studies show a novel role of ADAM23 in governing DC antigen presentation to cognate CD4⁺ T cells.

Scavenger receptor WC1 contributes to the γδ T cell response to Leptospira

WC1 molecules are exclusively expressed on the surface of γδ T cells. They belong to the scavenger receptor cysteine-rich (SRCR) superfamily and are encoded by a multi-gene family. WC1 molecules have been grouped on the basis of antibody reactivity. The expression of WC1 molecules from these serologically defined groups is correlated with differences in γδ T cell responses. The expression of receptors within the WC1.1 group correlates with the capacity of γδ T cells to respond to Leptospira antigen. In this study, we used RNA interference to directly investigate the role of WC1 expression in the response to Leptospira borgpetersenii. We found that when three out of thirteen WC1 gene products were downregulated by RNA interference, γδ T cell proliferation and IFN-γ production in response to Leptospira antigen was significantly reduced. Our data demonstrate that specific receptors in the WC1 family directly participate in Leptospira recognition and/or activation of γδ T cells.

gammadeltaTCR ligands and lineage commitment

Two major T lymphocyte lineages--alphabeta and gammadelta T cells--develop in the thymus from common precursors. Differentiation of both lineages requires signals coming from TCRs. Development of alphabeta T cells is driven at early stages by signaling from the pre-TCR, most likely in a ligand-independent fashion, and later--by signals delivered by alphabetaTCRs binding to their ligands--classical or non-classical MHC molecules. gammadelta lineage cells likewise require TCR signaling for their differentiation. Recent work from several groups suggests that TCR signaling not only ensures the developmental progression towards alphabeta and gammadelta lineages but that signal strength instructs lineage fate: weaker TCR signal results in alphabeta and stronger--in gammadelta lineage commitment. However, as most gammadeltaTCRs remain orphan receptors, it is still debated whether strong signals from gammadeltaTCRs in development are generated in a ligand-dependent manner (as in the case of alphabetaTCRs), ligand-independent manner (as for pre-TCR) or both. Here we summarize evidence supporting a possible role for ligands in gammadelta T cell lineage commitment and the generation of gammadelta sublineages.

Crocidolite induces prostaglandin I(2) release mediated by vitronectin receptor and cyclooxygenase-2 in lung cells

Interstitial lung disease (ILD) produces disruption of alveolar walls with loss of functionality and scar tissue accumulation. Asbestosis is the ILD produced by the inhalation of asbestos fibers. This study attempts to elucidate the role of lung epithelial cells in the generation of asbestos-induced ILD. When exposed to crocidolite LA-4 cells had a decrease in viability and an increase in the release of lactate dehydrogenase (LDH) and 6-keto PGF(1alpha), a PGI(2) metabolite. PGI(2) release was mediated by cyclooxygenase-2 (COX-2) and vitronectin receptor (VNR). When LA-4 cells were treated with VNR inhibitors, either RGD (Arg-Gly-Asp) peptide or VNR blocking antibody, a statistically significant decrease in PGI(2) metabolite production was observed, but crocidolite-induced cytotoxicity was not prevented. These findings propose that crocidolite is coated by an RGD protein and binds VNR-inducing COX-2 expression and PGI(2) release. Moreover, when LA-4 cells were exposed to crocidolite in the presence of reduced serum culture media, PGI(2) production was prevented, and when bronchoalveolar lavage fluid (BALF) was added, PGI(2) production was rescued. Cytotoxicity did not occur, either in reduced serum culture media or when BALF was added. In conclusion, crocidolite requires the presence of an RGD protein coating the fibers to induce inflammation (PGI(2) production) and crocidolite alone cannot induce cytotoxicity in lung cells.

Anti-inflammatory effects of alphav integrin antagonism in acute kidney allograft rejection

Integrin-mediated cell adhesion and signaling is essential to vascular development and inflammatory processes. Elevated expression of integrin alpha(v)beta(3) has been detected in ischemia-reperfusion injury and rejecting heart allografts. We thus hypothesized that the inhibition of alpha(v)-associated integrins may have potent anti-inflammatory effects in acute kidney allograft rejection. We studied the effects of a peptidomimetic antagonist of alpha(v) integrins in two rat models of renal allotransplantation, differing in degree of major histocompatibility complex mismatch. Integrin alpha(v)beta(3) was up-regulated in rejecting renal allografts. Integrin antagonist reduced the histological signs of acute rejection, the intensity of the mononuclear cell infiltration, and cell proliferation in the grafted kidneys. This could be correlated to a reduced leukocyte-endothelial interaction and an improved peritubular microcirculation observed by intravital microscopy. In vitro under laminar flow conditions, the arrest of monocytes to interleukin-1beta-activated endothelium was decreased. Furthermore, in co-culture models the proliferation and transmigration of monocytes/macrophages, endothelium, and fibroblasts induced by renal tubular epithelia was efficiently inhibited by alpha(v) integrin antagonism. These data reveal an important role of this integrin subclass in leukocyte recruitment and development and maintenance of acute rejection; blockade of alpha(v) integrins may provide a new therapeutic strategy to attenuate acute allograft rejection.

Beta 3 integrins regulate lymphocyte migration and cytokine responses in heart transplant rejection

Integrin alpha v beta 3 is important for cell survival, signaling and migration, particularly during angiogenesis and tumorigenesis, where it has been proposed as a therapeutic target. alpha v beta 3 is up-regulated following transplantation and beta 3 polymorphisms are associated with increased acute kidney rejection, suggesting that alpha v beta 3 may also play a role in transplant rejection. Here, using a model of allogeneic heart transplantation, we show that allograft survival is prolonged in beta 3 integrin-deficient (beta 3(-/-)) mice. This is associated with Th2-type immune responses and reduced T-cell infiltration into grafts and T cells from beta 3(-/-) mice show impaired adhesion and migration, consistent with a role for alpha v beta 3 in transmigration. These studies provide evidence that targeting beta 3 integrins impairs recruitment of effector cells and alters cytokine production, so prolonging graft survival. We also show that low doses of blocking antibodies against leukocyte function associated antigen-1 (LFA-1)/alpha L beta 2 and very late antigen-4 (VLA-4)/alpha 4 beta 1, when combined with deletion of beta 3, lead to long-term survival of allografts with no evidence of chronic rejection. Hence we provide strong mechanistic evidence supporting previous genetic studies, demonstrate the involvement of beta 3 integrins in both acute and chronic rejection and identify beta 3 as a new target for immunosuppressive therapy.

Hybridomas expressing gammadelta T-cell receptors respond to cardiolipin and beta2-glycoprotein 1 (apolipoprotein H)

Hybridomas expressing murine gammadelta T-cell receptors were found to produce cytokines in response to cardiolipin (CL) and structurally related anionic phospholipids. This response required serum at concentrations related to the amount of CL in cultures. The purified serum factor, beta2-glycoprotein 1 (beta2-GP1) (apolipoprotein H), supported the CL response alone, whereas several other serum proteins and ovalbumin did not. beta2-GP1 is known to form complexes with anionic phospholipids, particularly CL, which are often recognized by pathological autoantibodies. We speculate that gammadelta T cells also recognize such complexes and that the hybridoma response reported here reflects this specificity.

None of the integrins known to be present on the mouse egg or to be ADAM receptors are essential for sperm-egg binding and fusion

Antibody inhibition and alpha6beta1 ligand binding experiments indicate that the egg integrin alpha6beta1 functions as a receptor for sperm during gamete fusion; yet, eggs null for the alpha6 integrin exhibit normal fertilization. Alternative integrins may be involved in sperm-egg binding and fusion and could compensate for the absence of alpha6beta1. Various beta1 integrins and alphav integrins are present on mouse eggs. Some of these integrins are also reported to be receptors for ADAMs, which are expressed on sperm. Using alpha3 integrin null eggs, we found that the alpha3beta1 integrin was not essential for sperm-egg binding and fusion. Oocyte-specific, beta1 integrin conditional knockout mice allowed us to obtain mature eggs lacking all beta1 integrins. We found that the beta1 integrin null eggs were fully functional in fertilization both in vivo and in vitro. Furthermore, neither anti-mouse beta3 integrin function-blocking monoclonal antibody (mAb) nor alphav integrin function-blocking mAb inhibited sperm binding to or fusion with beta1 integrin null eggs. Thus, function of beta3 or alphav integrins does not seem to be involved in compensating for the absence of beta1 integrins. These results indicate that none of the integrins known to be present on mouse eggs or to be ADAM receptors are essential for sperm-egg binding/fusion, and thus, egg integrins may not play the role in gamete fusion previously attributed to them.

Acute cellular rejection following human heart transplantation is associated with increased expression of vitronectin receptor (integrin alphavbeta3)

The vitronectin receptor (integrin alphavbeta3), a cell-surface adhesion receptor, has been shown to play a significant role in endothelial cell migration, apoptosis, atherosclerosis, and T-lymphocyte activation. This study was undertaken to test the hypothesis that cardiac allograft rejection is associated with increased expression of alphavbeta3. We also determined whether fibronectin receptor (alpha5beta1) and tissue factor are up-regulated in the presence of acute cellular rejection. We evaluated endomyocardial biopsy specimens with histologic evidence of different degrees of acute cellular rejection (grade 0, n = 10; grade 1A, n = 10; grade 2, n = 10; grade 3A, n = 10). Biopsies were obtained 2-4weeks after cardiac transplantation. Immunoperoxidase staining was performed for alphavbeta3, tissue factor, and alpha5beta1, and protein levels were further determined by Western blot analysis. Specimens with grade 2 and grade 3A rejection showed positive staining of alphavbeta3 in lymphocytic aggregates and vascular endothelial cells. By immunoblotting, we identified significantly increased expression of alphavbeta3 in the presence of acute rejection, grade 2 (3-fold, p = 0.01) and grade 3A (3.6-fold, p = 0.005) compared to grade 0 and 1 A specimens. There was no evidence of increased expression of alpha5beta1 or tissue factor. Acute cellular rejection, a process characterized by T-lymphocyte activation and release of inflammatory cytokines, is associated with increased expression of alphavbeta3.

Costimulation by extracellular matrix proteins determines the response to TCR ligation

Although ligation of the T-cell antigen receptor (TCR) is central to the responsiveness and antigen specificity of T-cells, it is insufficient to elicit a response. To determine whether the need for costimulation reflects inadequate strength of signal transduction through the TCR or an absolute block of signaling in the absence of a coligand, we studied T-cell activation under serum-free conditions eliminating costimulation by various extracellular matrix proteins which otherwise have an omnipresent and frequently overlooked effect. Engagement of the TCR leads to induction of Fas, but not to measurable IL-2 secretion or apoptosis. Those activation parameters are induced by costimulation through integrin alphaVbeta3. Furthermore, T-cell survival or elimination is determined by the type of ligand binding to this coreceptor with vitronectin, fibronectin, and fibrinogen efficiently inducing apoptosis and IL-2 production while osteopontin and entactin mediate IL-2 secretion comparably without causing programmed cell death. Consistent with the cytokine properties of these ligands, differential costimulation depends on their presentation in soluble rather than immobilized form. The determination of elimination versus survival of activated T-cells by coligation of beta3-integrins may have bearing on the fundamental postthymic mechanisms that shape the T-cell repertoire.

Selective regulation of integrin--cytoskeleton interactions by the tyrosine kinase Src

Cell motility on extracellular-matrix (ECM) substrates depends on the regulated generation of force against the substrate through adhesion receptors known as integrins. Here we show that integrin-mediated traction forces can be selectively modulated by the tyrosine kinase Src. In Src-deficient fibroblasts, cell spreading on the ECM component vitronectin is inhibited, while the strengthening of linkages between integrin vitronectin receptors and the force-generating cytoskeleton in response to substrate rigidity is dramatically increased. In contrast, Src deficiency has no detectable effects on fibronectin-receptor function. Finally, truncated Src (lacking the kinase domain) co-localizes to focal-adhesion sites with alpha v but not with beta 1 integrins. These data are consistent with a selective, functional interaction between Src and the vitronectin receptor that acts at the integrin-cytoskeleton interface to regulate cell spreading and migration.

Laminin 5 promotes activation and apoptosis of the T cells expressing alpha3beta1 integrin

By introducing an alpha3 gene-containing plasmid into a human T cell line Jurkat, we prepared the T cells, which express a high level of the alpha3beta1 integrin, to assess the role of laminin 5 in the skin immune system. The alpha3beta1-expressing T cells adhered to laminin 5 and exhibited spreading. These adhered T cells showed a significant tyrosine phosphorylation of intracellular proteins including p59(fyn) upon T-cell receptor (TCR) stimulation. Six hours after cross-linking TCR, these cells on laminin 5 secreted a three times higher level of IL-2 than those on a BSA-coated plate. Twenty hours after the stimulation, 48% of the alpha3beta1-expressing T cells on laminin 5 caused apoptosis. The protein level of cyclin D3 and E decreased, while that of p53 increased in these T cells. These data suggest that laminin 5 may play at least two regulatory roles for T cell functions: augmentation of IL-2 production by antigen-stimulated T cells and induction of apoptosis in these T cells.

Activation and control of self-reactive gammadelta T cells

Mammalian and avian CD3+ T cells can be separated into two lymphocyte subsets bearing heterodimeric T-cell receptors (TCR) composed of either alphabeta or gammadelta chains. Although it is now widely accepted that gammadelta and alphabeta T cells fulfill mandatory and nonredundant roles, the generality of this assumption and the exact functions played by gammadelta T cells remain uncertain. While an early protective role of gammadelta T cells has long been suspected, recent observations drawn in particular from transgenic models suggest their implication in the homeostatic control of immune and nonimmune processes. This hypothesis is also supported by the existence of several self-reactive gammadelta T-cell subsets in rodents and humans, whose specificity and effector properties will be detailed and discussed here. The present review will also describe several mechanisms that could allow efficient control of these self-reactive subsets while permitting expression of their regulatory and/or protective properties.

Adhesion and signaling mediated by the cytoplasmic tails of leucocyte integrins

Integrins not only mediate cell adhesion but also contribute to a variety of other cellular processes including proliferation, cytokine production, cytotoxicity and apoptosis. They act as bi-directional signal transducers, mediating signaling from inside-to-outside the cell and from outside-to-inside the cell. Evidence is emerging that signaling through leukocyte integrins (beta 2 and beta 7) is distinct from signaling by the more widely distributed beta 1 integrins. Here we discuss the role of the cytoplasmic domains of leukocyte integrins and that of cytosolic proteins that bind integrins in mediating signal transduction. Distinct sites in the alpha as well as the common beta chain contribute to this process. We also show that beta 2 integrin distribution on the cell surface is of particular relevance for leukocytes to rapidly alter their adhesive state and display their highly dynamic adhesive behavior. From these and recently published findings the picture is arising that particular cell functions may be supported by integrin-specific signaling pathways.

Integrin-mediated ras-extracellular regulated kinase (ERK) signaling regulates interferon gamma production in human natural killer cells

Recent evidence indicates that integrin engagement results in the activation of biochemical signaling events important for regulating different cell functions, such as migration, adhesion, proliferation, differentiation, apoptosis, and specific gene expression. Here, we report that beta1 integrin ligation on human natural killer (NK) cells results in the activation of Ras/mitogen-activated protein kinase pathways. Formation of Shc-growth factor receptor-bound protein 2 (Grb2) and Shc-proline-rich tyrosine kinase 2-Grb2 complexes are the receptor-proximal events accompanying the beta1 integrin-mediated Ras activation. In addition, we demonstrate that ligation of beta1 integrins results in the stimulation of interferon gamma (IFN-gamma) production, which is under the control of extracellular signal-regulated kinase 2 activation. Overall, our data indicate that beta1 integrins, by delivering signals capable of triggering IFN-gamma production, may function as NK-activating receptors.

Surfactant protein A inhibits T cell proliferation via its collagen-like tail and a 210-kDa receptor

Investigation of possible mechanisms to describe the hyporesponsiveness of pulmonary leukocytes has led to the study of pulmonary surfactant and its constituents as immune suppressive agents. Pulmonary surfactant is a phospholipid-protein mixture that reduces surface tension in the lung and prevents collapse of the alveoli. The most abundant protein in this mixture is a hydrophilic molecule termed surfactant-associated protein A (SP-A). Previously, we showed that bovine (b) SP-A can inhibit human T lymphocyte proliferation and interleukin-2 production in vitro. Results presented in this investigation showed that different sources of human SP-A and bSP-A as well as recombinant rat SP-A inhibited human T lymphocyte proliferation in a dose-dependent manner. A structurally similar collagenous protein, C1q, did not block the in vitro inhibitory action of SP-A. The addition of large concentrations of mannan to SP-A-treated cultures also did not disrupt inhibition, suggesting that the effect is not mediated by the carbohydrate recognition domain of SP-A. Use of recombinant mutant SP-As revealed that a 36-amino acid Arg-Gly-Asp (RGD) motif-containing span of the collagen-like domain was responsible for the inhibition of T cell proliferation. A polyclonal antiserum directed against an SP-A receptor (SP-R210) completely blocked the inhibition of T cell proliferation by SP-A. These results emphasize a potential role for SP-A in dampening lymphocyte responses to exogenous stimuli. The data also provide further support for the concept that SP-A maintains a balance between the clearance of inhaled pathogens and protection against collateral immune-mediated damage.

Cross talk between alpha(v)beta3 and alpha4beta1 integrins regulates lymphocyte migration on vascular cell adhesion molecule 1

Local inflammation leads to increased expression of the vascular cell adhesion molecule (VCAM)-1 on vascular endothelium which contributes to the encapture of leukocytes from the circulating blood through the leukocyte ligand alpha4beta1 integrin. Inflammatory vascular endothelium expresses VCAM-1 at high density. We found that the speed of locomotion of activated lymphocytes migrating along surfaces coated with recombinant VCAM-1 at a comparable density to that found on inflammatory endothelium was slow. However, lymphocytes do migrate and extravasate rapidly under inflammatory conditions, indicating that there must be mechanisms that regulate the interaction between alpha4beta1 and VCAM-1 in vivo. Here we show that the lymphocyte alpha(v)beta3 integrin and integrin-associated protein (IAP) is able to regulate this interaction. The occupancy of lymphocyte alpha(v)beta3 integrin by platelet cell adhesion molecule-1 or vitronectin regulated the speed of alpha4beta1 integrin-dependent locomotion of lymphocytes on recombinant VCAM-1. This allowed rapid lymphocyte migration at VCAM-1 densities which are typical of inflammatory vessels. This alpha(v)beta3-mediated enhanced migration of lymphocytes via alpha4beta1 is likely to depend on the interaction of alpha(v)beta3 integrin with the IAP. Furthermore, this motile process correlates with polarization of the actin cytoskeleton in lymphocytes. Our results suggest that cross talk between alpha(v)beta3 integrin and alpha4beta1 integrin is a mechanism in the regulation of lymphocyte locomotion along inflammatory endothelium and subsequent transendothelial migration. This can explain how lymphocytes overcome tight adhesion to the vascular endothelium and start rapid migration along and through the endothelial lining of blood vessels into inflammatory tissue.

Modulation of the expression of integrins on glial cells during experimental autoimmune encephalomyelitis. A central role for TNF-alpha

Integrins comprise a group of adhesion receptors involved in cell-cell and cell-extracellular matrix interactions. Evidence is accumulating that integrins expressed on mononuclear cells play a central role in the induction of autoimmune diseases of the central nervous system. The effects of integrins on glial cell behavior, myelination, and angiogenesis suggest that they may also have a role in resolving inflammation in the nervous system and in promoting tissue repair. We investigated the temporospatial expression of integrins in the rat central nervous system during the course of experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis. A higher expression of alpha v- and beta 4-integrin subunits in astrocytes and alpha 2 integrin in oligodendrocytes was observed in active lesions of experimental autoimmune encephalomyelitis, in comparison with controls. Proinflammatory cytokines, primarily TNF-alpha, also enhanced alpha v, beta 4, and alpha 2 expression in purified glial cells ex vivo. Furthermore, we observed that the expression of some integrin subunits was modulated in the cerebral vasculature during inflammation. Our results suggest an active role for glial and vascular integrins in the regulation of autoimmune diseases of the central nervous system, opening an avenue for new potential immunotherapies.

Cytotoxic T-lymphocyte interaction with fibronectin and vitronectin: activated adhesion and cosignalling

Stimulation of cloned cytotoxic T lymphocytes (CTL) with anti-T-cell receptor (TCR) monoclonal antibody (mAb) in solution resulted in rapid and sustained activation of adhesion to immobilized fibronectin (FN) but did not initiate degranulation. Addition of a second antibody (Ab) to further cross-link the TCR substantially increased the level of adhesion and also activated degranulation, as measured by release of serine esterase, in the presence of immobilized FN but not in its absence. Thus, binding to FN can provide a costimulatory signal to activate degranulation. TCR cross-linking also activated CD8-dependent adhesion to class I, and CD8 provided a costimulatory signal upon binding to class I. However, the requirements for activating adhesion and generating the costimulatory signal differed significantly for FN versus class I ligand, suggesting that these two receptor-ligand systems do not share a common mechanism of action. Co-immobilizing FN and alloantigen resulted in increased serine esterase release in comparison with that stimulated by antigen alone, and required the FN and class I be on the same surface. Peptide and antibody blocking demonstrated that CTL binding to FN, and to vitronectin (VN), was mediated by the alpha V beta 3 vitronectin receptor (VNR). Thus, VNR is activated by a signal from the TCR to mediate adhesion to FN or VN, and delivers a costimulatory signal for degranulation via a different mechanism than costimulation by CD8 binding to class I.

Cytotoxic T lymphocytes express a beta3 integrin which can induce the phosphorylation of focal adhesion kinase and the related PYK-2

Fibronectin has been shown to stimulate tyrosine phosphorylation of a number of proteins in the 115-125 kDa range and facilitate degranulation by alloantigen-specific cytotoxic T lymphocyte (CTL) clones in response to substimulatory amounts of anti-CD3 or anti-T cell receptor (TCR). The current study was initiated to further characterize integrin expression and usage by these CTL clones. We demonstrate that vitronectin and fibrinogen, but not laminin or collagen, are also able to both facilitate degranulation in the presence of substimulatory anti-CD3 and stimulate tyrosine phosphorylation of these 115-125-kDa proteins, with a 115-kDa protein being the most prominently phosphorylated. These results implicate the expression and usage of the vitronectin receptor, alpha beta3 integrin, by these CTL clones. We demonstrate by both flow cytometry and immunoprecipitation that CTL clones do in fact express beta3 integrin. Immobilized antibody to beta3 stimulates the phosphorylation of the 115-125-kDa proteins, suggesting that engagement of beta3 transmits the same signal into these cells as fibronectin or vitronectin. The fibronectin and vitronectin-induced phosphorylation as well as adhesion to either fibronectin or vitronectin can be significantly inhibited with antibodies to beta3 integrins. Finally, we are able to immunoprecipitate 115-kDa proteins with antiserum to focal adhesion kinase and a related kinase, called PYK-2, that becomes phosphorylated in response to vitronectin or immobilized anti-beta3. Taken together, these results demonstrate that CTL express and use beta3-integrins as signaling molecules which can augment TCR-mediated stimulation.

Expression of alpha v and beta 3 integrin chains on murine lymphocytes

The vitronectin receptor is a member of the integrin family of adhesion protein receptors and binds a broad spectrum of ligands, including fibronectin and fibrinogen in addition to vitronectin. We have generated four mAbs that recognize the murine alpha v beta 3 vitronectin receptor. Biochemical and expression analyses showed that two of the mAbs are specific for the alpha v chain, and two are specific for the beta 3 chain. The mAbs are effective blocking reagents and inhibited cell adhesion to vitronectin, fibrinogen, and fibronectin. Staining analysis revealed expression of alpha v and beta 3 on certain populations of murine thymocytes, splenocytes, and bone marrow cells. The expression of alpha v and beta 3 appeared to be modulated at specific stages of thymocyte development, suggesting a possible function for the alpha v beta 3 vitronectin receptor in T cell development.

New concepts in the immunology of sickle cell disease

OBJECTIVE

Our objective is to review the role of adhesion molecules, cytokines, and inflammation in the abnormal adherence of sickle red blood cells to vascular endothelia in the pathogenesis of vascular complication in patients with sickle cell anemia.

DATA SOURCES

The MEDLINE database was used to review the hematologic, immunologic, and allergy literature in English with respect to the adhesion molecules involved in sickle hematopoiesis and vascular complications.

STUDY SELECTION

Studies selected for review were those that identified the adhesion molecules involved in reticulocyte-endothelial adhesion and the influence that cytokines, infections, and atopy have upon the expression of these molecules.

RESULTS

In sickle cell disease, a constant low level of inflammation caused by abnormal adhesion of sickle erythrocytes to endothelial cells in the microvasculature produces low-level tissue ischemia. Allergic and infectious inflammations are likely to lead to increased sickle erythrocyte trapping in the microvascular endothelia which progresses to vessel obstruction, end organ ischemic damage, and dysfunction.

CONCLUSION

The identification of underlying immune defects that predispose patients to infections and inflammation needs to be emphasized. Anti-inflammatory medications, anti-adhesion molecule monoclonal antibodies, and adhesion molecule binding-site analogs may have a future in the treatment of the acute vascular complications of sickle cell disease.

CD48 may serve as an accessory molecule for the activation of a subset of human gamma/delta T cells

To further assess the role of CD48 in the interaction of human gamma/delta T cells with their specific target, we generated two series of alloreactive clones, L and K. These clones express a V1-D-J1-C delta chain associated to V3-J2-C2 (L) or V2-J2-C2 (K) gamma chain. Functionally they were CTLs able to lyse the sensitizing B-cell line E418. The cytotoxicity of the L and K clones toward E418 was inhibited by anti-CD48 mAb. That of the L clones was also inhibited by anti-HLA class I mAbs. Variation in L and K lysis profile was observed against a panel of CD48+ targets, further strengthening the argument that they display distinct specificities and suggesting that they do not recognize CD48. Heterogeneity in TCR gene segment usage, MHC-dependent recognition of E418 by the L clones, and resistance of some CD48+ targets strongly suggest that CD48 itself does not interact with L and K TCR. Transfection of CHO cells with CD48 induced killing by the K clones. This killing was inhibited by anti-CD48 mAbs. Taking into account the recent reports on CD48 as an accessory molecule, our results suggest that by binding to CD2 (and/or an unknown ligand), CD48 may serve to strengthen E/T interaction and may contribute to the activation of a minor subset of gamma/delta T cells.

The vitronectin receptor (alpha V beta 3) as an example for the role of integrins in T lymphocyte stimulation

Integrins are a family of cell surface receptors which mediate the adhesion of cells to each other or to extracellular matrix (ECM) proteins. The interaction of integrins with their ligands or counter-receptors was initially considered to be a one-way process in that cells actively regulate the interaction of integrins with their ligands ('inside-out signal'). In contrast, it was not obvious that cells would receive a signal from the outside via the integrin heterodimers following ligand binding ('outside-in signal'). Recent evidence increasingly supports the active role of integrins in cell activation and proliferation. Many reports describe the effects of integrin-mediated signaling in lymphoid cells. Our studies of gamma/delta T cells, expressing the beta 3 integrin vitronectin receptor (VNR), reflect some of the consequences this active interaction between lymphocytes and the ECM could have for T cell activation and differentiation. The VNR has been described as a T cell costimulatory molecule. We recently reported that the VNR has the potential to stimulate cytokine secretion in T cell hybridomas without involvement of T cell receptor-mediated signals. Further studies demonstrated tyrosine phosphorylation of proteins following VNR cross-linking and the interaction of the VNR with protein kinases. Intensive research focuses on the signal transduction mechanisms of integrins and their interaction with other costimulatory or activation molecules. This knowledge is important to better understand the role of adhesion molecules, the ECM, and the cellular microenvironment for lymphocyte activation and differentiation.

Developmental heterogeneity of V gamma 1.1 T cells in the mouse liver

Modifications at V-(D)-J junctions increase the diversity of T-cell receptors (TCR). It has been shown that the levels of N-nucleotide insertion at the V-(D)-J junction in TCR transcripts are different between fetal and adult stages. To clarify developmental stages and pathways of gamma delta T cells in the liver, we analysed the nucleotide sequence of V gamma 1.1-J gamma 4 junctions of intra-hepatic lymphocytes (IHL), spleen cells and developing thymocytes from normal and athymic nude mice. The level of N-insertion increased in thymocytes during ontogeny. The percentage of V gamma 1.1-J gamma 4 transcripts with N-insertion was 3% at day 16 of gestation, 42% at newborn, and 89% at 7 weeks. Transcripts from normal IHL showed intermediate levels of N-insertion between those of newborn and adult thymocytes. In contrast the percentage of N-insertion in nude IHL was 47%, and this value was comparable to that of newborn thymocytes. Among the transcripts of normal IHL, the sequences common with nude IHL showed a newborn level of N-insertion (38%), and the remaining sequences showed an adult level (89%). These results suggested the possibility that V gamma 1.1-expressing T cells in IHL might be a heterogeneous population consisting of the cells developed extrathymically as well as the cells developed intrathymically. The V gamma 1.1-J gamma 4 junctions from spleen cells showed less variability than those from IHL and adult thymocytes. It suggested that gamma delta T cells bearing specific V gamma 1.1 TCR develop and/or home in the spleen.

Bovine gamma/delta T-cell proliferation is associated with self-derived molecules constitutively expressed in vivo on mononuclear phagocytes

Bovine gamma/delta T cells have been shown previously to proliferate when cocultured with gamma-irradiated bovine monocytes in the 'autologous mixed leucocyte reaction' (AMLR). It was suggested that the response may be to culture-derived or culture-induced antigenic epitopes. Data presented here indicate that the gamma/delta T-cell stimulatory activity is attributable to a self-derived cell-surface molecule of mononuclear phagocytes that is constitutively expressed in vivo. The ability to induce an AMLR did not require in vitro culture or stress associated with in vitro isolation of cells or increased temperature since it could be induced by monocytes fixed by paraformaldehyde during blood collection from normal animals. Furthermore, stimulation by monocytes did not depend upon secreted molecules since fixed monocytes that had been incubated overnight at 37 degrees to allow secretion of preformed molecules, or subjected to hypotonic shock in H2O for 10 min before addition to the cultures, induced an AMLR as did plasma membranes prepared from ex vivo monocytes. In contrast, enzymatic treatment of monocytes to digest surface molecules followed by fixation destroyed their ability to stimulate an AMLR. The ability of monocytes to stimulate proliferation of gamma/delta T cells was distinguishable from their ability to stimulate alpha/beta T cells, since the former was destroyed by glutaraldehyde fixation whereas stimulation of alpha/beta T cells by major histocompatibility complex (MHC)-presented antigenic epitopes is not. Moreover, induction of proliferation of bovine gamma/delta T cells was not MHC-restricted. Finally, bovine alveolar macrophages, sheep monocytes and transformed bovine monocytes stimulated proliferation of bovine gamma/delta T cells whereas none of the following did so: human monocytes, murine macrophages, bovine myeloid cells other than mononuclear phagocytes, other nucleated cells found in bovine blood including activated MHC class II-bearing B cells, and a variety of species of bacteria. Thus, the stimulatory epitope is unique to and conserved among mononuclear phagocytes of ruminants. Demonstration of stimulation of bovine gamma/delta T cells by self-derived molecules is consistent with reports for murine gamma/delta T cells.

Evidence for the early recruitment of T-cell receptor gamma delta+ T cells during rat listeriosis

We have previously reported that heat-shock protein (hsp) 60-reactive T-cell receptor (TCR)gamma delta+ T cells appear in the peritoneal cavity during the early stage of infection with Listeria monocytogenes in mice. In this study, we examined the kinetics of TCR gamma delta+ T cells during listeriosis in F344 rats by flow cytometry using a V65 monoclonal antibody (mAb) directed to a constant determinant of rat TCR gamma delta chains. TCR gamma delta+ T cells significantly increased in the peritoneal cavity on day 6 and then decreased by day 10 after infection, in parallel with the kinetics of hsp60 expression in the peritoneal macrophages during listeriosis in F344 rats. Most of the early appearing TCR gamma delta+ T cells were of the CD4- CD8 alpha beta+ CD5+ lymphocyte function-associated antigen (LFA)-1 alpha high CD45RC- interleukin-2 receptor (IL-2R) alpha- phenotype, although a significant fraction of the TCR gamma delta+ T cells expressed CD8 alpha only. The increase in TCR gamma delta+ T cells during listeriosis was prominent in F1 (F344 x Lewis) rats but only marginal in Lewis rats, which was correlated with the expression level of hsp 60 in the peritoneal macrophages. The peritoneal TCR gamma delta+ T cells in naive F344 rats appeared to proliferate significantly in response to recombinant hsp 60 (rhsp 60) derived from Mycobacterium bovis bacillus Calmette-Guérin (BCG). These results imply that the early appearance of hsp 60-reactive TCR gamma delta+ T cells during listerial infection can be generalized across species.

Different expression of E-cadherin by two cutaneous gamma/delta TcR+ T-cell subsets, V gamma 5- and V gamma 5+ gamma/delta TcR+ T cells

Recently we have demonstrated that, besides V gamma 5+ gamma/delta TcR+ T cells (V gamma 5+ gamma/delta T cells), V gamma 5- gamma/delta TcR+ T cells (V gamma 5- gamma/delta T cells) are also present in murine skin. In the present study, to characterize the functional differences between these two different cutaneous gamma/delta T cells we examined the expression pattern of E-cadherin and its two integrins. After co-culturing of Ly-5+ epidermal cells and migrating cells from organ-cultured murine skin with cutaneous stromal cells, we could expand V gamma 5+ gamma/delta T cells and V gamma 5- gamma/delta T cells, respectively. Flow cytometry demonstrated that cultured V gamma 5+ gamma/delta T cells expressed E-cadherin, but V gamma 5- gamma/delta T cells did not. This difference in E-cadherin expression was also observed in freshly isolated V gamma 5+ and V gamma 5- gamma/delta T cells. On the other hand, both V gamma 5+ and V gamma 5- gamma/delta T cells expressed the alpha chain of the vitronectin receptor, but did not express the alpha 4 integrin. Of these two cutaneous gamma/delta T cells, only V gamma 5+ gamma/delta T cells adhered to murine keratinocyte cell line, PAM 212 cells. Unexpectedly, however, the adhesion of E-cadherin-expressing V gamma 5+ gamma/delta T cells to PAM 212 cells was not inhibited by anti-E-cadherin antibody, which effectively abrogated the adhesion of Langerhans cells to PAM 212 cells. These distinct phenotypic and functional characteristics in the sub-sets of cutaneous gamma/delta T cells may suggest that they reside in different locations in the skin to play different functional roles in skin immunophysiology.

CD31/PECAM-1 is a ligand for alpha v beta 3 integrin involved in adhesion of leukocytes to endothelium

To protect the body efficiently from infectious organisms, leukocytes circulate as nonadherent cells in the blood and lymph, and migrate as adherent cells into tissues. Circulating leukocytes in the blood have first to adhere to and then to cross the endothelial lining. CD31/PECAM-1 is an adhesion molecule expressed by vascular endothelial cells, platelets, monocytes, neutrophils, and naive T lymphocytes. It is a transmembrane glycoprotein of the immunoglobulin gene superfamily (IgSF), with six Ig-like homology units mediating leukocyte-endothelial interactions. The adhesive interactions mediated by CD31 are complex and include homophilic (CD31-CD31) or heterophilic (CD31-X) contacts. Soluble, recombinant forms of CD31 allowed us to study the heterophilic interactions in leukocyte adhesion assays. We show that the adhesion molecule alpha v beta 3 integrin is a ligand for CD31. The leukocytes revealed adhesion mediated by the second Ig-like domain of CD31, and this binding was inhibited by alpha v beta 3 integrin-specific antibodies. Moreover alpha v beta 3 was precipitated by recombinant CD31 from cell lysates. These data establish a third IgSF-integrin pair of adhesion molecules, CD31-alpha v beta 3 in addition to VCAM-1, MadCAM-1/alpha 4 integrins, and ICAM/beta 2 integrins, which are major components mediating leukocyte-endothelial adhesion. Identification of a further versatile adhesion pair broadens our current understanding of leukocyte-endothelial interactions and may provide the basis for the treatment of inflammatory disorders and metastasis formation.

Immunobiology of mouse dendritic epidermal T cells: a decade later, some answers, but still more questions

Over the past decade, overwhelming evidence has accumulated in many species, most notably in mice, that epithelial sites such as skin, intestine, and reproductive tract are populated with relatively discrete subsets of gamma delta cells. Such studies have identified several distinguishing and, in some cases, unique features of the dendritic epidermal T cells (DETC) populating the skin of all normal mice: homogeneous V5-J1-C gamma 1/V1-D2-J2-C delta T-cell receptors devoid of junctional diversity, apparent tissue restriction in adult mice to the skin, an important role for active hair growth in their localization and/or proliferation in the skin, and a capacity to recognize an antigen expressed on stressed epidermal cells. These properties have led to the hypothesis that DETC play distinctive roles in cutaneous immune surveillance and/or immunoregulation via recognition of a common self-antigen expressed by adjacent cells under various potentially harmful circumstances. Despite substantive advances in our knowledge about gamma delta cells in general (e.g., recent evidence that their manner of antigen recognition may be fundamentally different from that used by conventional alpha beta T cells) and about epithelial-specific subsets such as murine DETC in particular, it is clear that, compared with our understanding of alpha beta cells, major gaps still exist in our understanding of these cells. Persisting questions about DETC include: precise identification of the ligands for their homogenous T-cell receptors, the cellular and molecular requirements for their activation, their full range of functional activities, the reason(s) for the absence in normal human skin of a precise morphologic and phenotypic homologue, and, perhaps most important, their biologically relevant role(s) in cutaneous physiology, immunity, and/or pathology.

Activation of murine epidermal gamma delta T cells through surface 2B4

Dendritic epidermal T cells (DETC) are gamma delta T cells that normally reside in murine skin. They express on their surface the 2B4 molecule, a 66-kDa glycoprotein of the immunoglobulin gene superfamily thought to be associated with anti-tumor cytotoxicity by natural killer and lymphokine-activated killer cells. Here, we show that ligation of surface 2B4 transduces cell activation signals in DETC. Treatment with anti-2B4 monoclonal antibodies triggers the secretion of interferon-gamma and interleukin-2 by DETC lines, induces proliferation of resting DETC lines, amplifies anti-CD3-dependent proliferation of DETC freshly isolated from mouse skin; and up-regulates egr-1 and c-fos mRNA expression. These results indicate a unique pathway for DETC activation.

Constitutive alpha V beta 3 integrin-mediated adhesion of human lymphoid B cells to vitronectin substrate

Adherence to cells and matrices participates in lymphocyte migration and tissue localization and contributes to the regulation of growth and differentiation of the lymphoid cells. The adherence is mainly mediated by three families of cell-surface proteins: integrins, immunoglobulin (Ig)-related molecules, and selectins. Integrins recognize Ig-related molecules such as ICAMs as well as fibronectin (FN), vitronectin (VN), and other matrix proteins. In this study, the in vitro adhesive properties of two Epstein-Barr virus-carrying B lymphoblastoid cell lines, IB-4 and NAD-20, were compared. IB-4 cells grow as a monolayer in contrast to NAD-20 cells, which grow as cell clusters. IB-4 cells were found to adhere to the tissue culture vessel through a component of the fetal bovine serum. By using blocking monoclonal antibodies to cell-surface molecules and serum proteins, IB-4 cells were found to use alpha V beta 3 integrin (CD51/CD61) and serum VN as the adhesive molecules. alpha V beta 3 integrin also mediated adhesion of IB-4 cells to human serum VN and to purified VN and FN. This constitutive adherence was not enhanced by phorbol ester treatment and was inhibited by RGD-containing peptides, in contrast to the homotypic adhesion of NAD-20 cells, which was mediated by beta 2 integrin CD11a/CD18 and its ligand ICAM-1 (CD54). Since VN is a component of both lymphoid tissue matrix and plasma, adhesion to this protein may affect functions and activities of B lymphocytes.

Interaction between gamma delta T cells and B cells regulating IgG production

Despite profound knowledge about the molecular structure of the gamma delta T-cell receptor (TCR), the physiological function of gamma delta T cells remains enigmatic. Participation of these cells in complex immune reactions, however, is suggested by the appearance of gamma delta T cells in sites of infectious and autoimmune-induced inflammations. Only a few in vitro models of gamma delta T-cell stimulation have been established: besides a reactivity in the presence of microbial ligands, human gamma delta T cells proliferate upon in vitro challenge with cells from an allogeneic B-lymphoblastic cell line (B-LCL). We present data here demonstrating that this reactivity is not confined to allogenic B-LCL. Autologous B-LCL are also very strong stimulators for gamma delta T cells; more important, autologous B cells can stimulate gamma delta T cells after a period of mitogen-activation but not in a resting state. This activation seems to address a subgroup of gamma delta T cells, as the percentage of V delta 1+ cells is increased after stimulation. Activated gamma delta T cells, on the other hand, are able to exert an influence on B cells by inhibiting the secretion of IgG in coculture experiments. These data define a simple regulatory circle of B cells and gamma delta T cells in vitro and propose a model for gamma delta T-cell function which could explain many in vivo observations of gamma delta T-cell activation.

Role of T cells and cytokines in effecting fibrosis

A number of humoral and cellular immune abnormalities are present in patients with early scleroderma (systemic sclerosis). Most of these abnormalities reflect ongoing autoimmune reactions of the cellular and humoral types, resulting in a variety of autoantibodies to cellular and tissue constituents. Evidence exists for a defect(s) in immunoregulation favoring excessive helper T cell activity. The presence of circulating cytokines and shed interleukin-2 receptors suggest ongoing cellular immune reactions are occurring, generating cytokines and lymphokines that are capable of effecting the vascular and fibrotic lesions that are hallmarks of the disease. Future directions for research are suggested that would focus on determining if, and at what point, fibroblasts might function autonomously to generate excessive matrix components and on determining the nature of the original antigenic stimulus that starts the scleroderma process.

Increased number of dendritic epidermal T cells associated with induced anagen phase of hair cycles

With the use of immunofluorescent staining we investigated the number and the morphologic and phenotypic changes of murine dendritic epidermal T cells (DETC) at various phases of the hair cycle that were synchronized by depilation. The epidermis on day 1 after depilation contained a small number of DETC, round DETC populated at perifollicular space on day 7, and then a large number of DETC with conspicuous dendrites were found mainly at interfollicular space on day 10. This suggests that the in situ proliferation of DETC may be correlated at least partly to the hair cycle, and that hair follicles, which are major skin appendages, may be involved in cutaneous immunity.

Response of a murine epidermal V gamma 1/V delta 6-TCR+ hybridoma to heat shock protein HSP-60

In the epidermis, the major population of T lymphocytes expresses a T-cell receptor (TCR) with V gamma 5 and V delta 1 variable regions, which is unique to this tissue. Roberts et al and Ezquerra et al, also describe a minor population of gamma delta-TCR+ cells in the epidermis that expresses a V gamma 1/V delta 6 TCR. These cells are different from other epidermal T cells in that they "spontaneously" produce cytokines, a result thought to be due to autoreactivity. Over the past 5 years, our laboratory has produced V gamma 1/V delta 6+ T-cell hybridomas from many tissue sources. These spontaneously produce cytokines but also are activated by heat shock protein (HSP-60)-derived peptides. Ezquerra et al report that none of their V gamma 1/V delta 6+ epidermal T-cell lines derived from C3H/HeN mice respond to HSP-60. Of the 99 gamma delta-TCR+ hybridomas we have produced from epidermal T cells of C57BL/6 mice, only one expressed the V gamma 1/V delta 6 TCR. This hybridoma, 70BET-2.12, not only spontaneously produces cytokines, but, unlike the V gamma 1/V delta 6-TCR+ epidermal T cells of Ezquerra et al, it also responds to the whole HSP-60 protein and a 17-mer HSP-60 peptide from M. leprae, producing increased levels of interleukin-2 of up to approximately ten-fold above the spontaneous level. This shows that V gamma 1/V delta 6-TCR+ epidermal T cells can respond to HSP-60. To confirm that 70BET-2.12 expresses TCR genes similar to those of cells that have HSP-60 reactivity, V gamma 1-C gamma 4 and V delta 6-C delta cDNA were produced from RNA isolated from this hybridoma, amplified by the polymerase chain reaction, and sequenced. The gamma and delta TCR gene sequences were similar but not identical to previously published sequences of HSP-60-reactive cells from lymphoid and other organs. No explanation can be found for the discrepancy between our findings and those of others at the level of TCR expression such that other strain-specific factors might be responsible for HSP-60 reactivity.

Different cytokine production profiles of gamma delta T cell clones: relation to inflammatory arthritis

This study was performed to investigate whether gamma delta T cells could also be divided into subsets, identified by a cytokine profile, as described for alpha beta T helper (Th) cell subsets. Cytokine production was studied in 22 gamma delta T cell clones obtained from the synovial fluid and peripheral blood of one patient with inflammatory arthritis and compared to that of 26 alpha beta T cell clones of the same and different patients. Interferon-gamma (IFN-gamma) was produced by 18 (82%) and interleukin-4 (IL-4) by 17 (77%) out of 22 gamma delta T cell clones, respectively. In contrast, IL-10 was not produced, except at very low level in one case. The mean levels of IL-4 were lower for clones derived from synovial fluid. When considering the production of IFN-gamma as an indicator of Th1 and that of IL-4 as an indicator of Th2, respectively, the most common pattern was a gamma delta Th1-like pattern, with the combination of high levels of IFN-gamma and low levels of IL-4. This pattern was found in V delta 1+ clones, all from synovial fluid. Additional patterns were also observed: a mixed, probably gamma delta Th0-like pattern with a more balanced production of both IFN-gamma and IL-4; a gamma delta Th1 pattern with the production of IFN-gamma alone; a gamma delta Th2 pattern with the production of IL-4 alone. These three patterns were also seen in blood gamma delta T cells which were all V delta 2, indicating that these patterns were independent of the V delta phenotype. gamma delta T cell clones produced lower levels of IFN-gamma (p = 0.001) and higher levels of IL-4 than alpha beta clones (p < 0.02). These differences in cytokine production between alpha beta and gamma delta subsets and within these subsets may contribute to their respective role in chronic inflammation.

Clones of tumor cells derived from a single primary human lung tumor reveal different patterns of beta 1 integrin expression

Previously we reported that over 75% of human non-small cell lung cancers overexpress the beta 1 integrin VLA-2 on their surface and show an increase in the mRNA encoding the alpha-2 chain of this integrin. These results suggested the possibility that the overproduction and overexpression of one or more of the beta 1 integrin may be involved in the pathogenesis of human lung tumors by modulating the invasive and/or metastatic potential of the tumor. We report here the generation and characterization of multiple clones of tumor cells derived from the primary culture of cells obtained from biopsy tissue of an aggressive human squamous cell lung tumor. We show that these tumor clones (or clonotypes) exhibit seven different yet stable phenotypes with respect to the expression of five members of the beta 1 integrin family. These results illustrate that a primary human lung tumor consists of multiple subpopulations of cells that while indistinguishable by ultrastructure are heterogeneous with respect to their beta 1 integrins. The availability of these distinct tumor clonotypes derived from a single tumor biopsy have made it possible to test the assumption that the beta 1 integrins play a role in tumor progression. The feasibility of this approach is demonstrated here by the intravenous inoculation of different human tumor clonotypes into severe combined immunodeficient (scid) mice. Our preliminary results with a pair of tumor clonotypes differing in VLA-1 and VLA-2 expression level reveal that the clonotype with high level of VLA-1 and VLA-2 displays a substantial increase in the experimental engraftment and metastasis of the human tumor cells in scid mice.

Adhesion receptors in lymphocyte activation

The past several years have seen significant progress in understanding the role of T lymphocyte coreceptors in adhesion and activation. New insights have been gained in several areas: the avidity regulation of beta 1 and beta 2 integrins and their role in signal transduction; the regulation of CD8 avidity; the role of Lck in CD4 coreceptor activity; and the novel role for CD2 adhesion in the T cell antigen response.

Contrasting roles for integrin beta 1 and beta 5 cytoplasmic domains in subcellular localization, cell proliferation, and cell migration

To carry out a detailed comparison of the roles of integrin beta 1 and beta 5 cytoplasmic domains, we expressed both wild type beta 1 and chimeric beta 1/5 constructs in CHO cells. In the latter, the cytoplasmic domain of beta 1 was replaced with that of beta 5. The human beta 1 and beta 1/5 constructs appeared at similar levels at the cell surface (mostly as alpha 5 beta 1 heterodimers) and contributed equally to CHO cell adhesion to fibronectin. However, beta 1 but not beta 1/5 localized to focal adhesion-like structures when CHO cells were spread on fibronectin. Furthermore, only the beta 1-CHO cells showed increased proliferation in response to fibronectin plus an integrin-activating anti-beta 1 antibody, and showed increased appearance of 32P-labeled protein (p90) that correlated with proliferation. In sharp contrast, the beta 1/5-CHO cells were notably more migratory than beta 1-CHO cells in a transwell haptotactic migration assay. These results indicate that the beta 1 and beta 5 integrin subunit cytoplasmic domains can translate similar adhesive information into highly contrasting subsequent events. Thus, we have established that "inside-out" and "outside-in" integrin signaling pathways are regulated by fundamentally distinct mechanisms. In addition, we suggest that the same properties of the beta 1 cytoplasmic domain that promote recruitment to visible focal adhesion-like structures may also be conductive to cell proliferation. Conversely, the properties of the beta 5 tail that make it less likely to localize into focal adhesion-like structures may contribute to enhanced cell migration.

Tolerance and self-reactivity in V gamma 1.1C gamma 4 transgenic mice

Immunological tolerance is the process of inhibiting or eliminating lymphocytes that recognize self-derived antigens. By removing potentially harmful self-reactive clones, this mechanism allows for the random generation of a diverse repertoire of T-cells capable of responding to foreign pathogens. Although all self-reactive T-cells should be removed from the repertoire, it is quite clear from many recent studies that a significant fraction of T-cells bearing gamma delta T-cell receptors (TCR) recognize self-derived antigens in normal healthy mice. The presence of self-reactive T-cells in healthy animals presents a paradox which may be explained by understanding the transient expression of the antigens (e.g., MHC class Ib, Heat Shock Proteins) that have been identified for gamma delta T-cells thus far. Data from experiments with V gamma 1.1C gamma 4 transgenic mice demonstrating the presence of self-reactive gamma delta T-cells and their influence on lymphoid development and immune surveillance will be examined in this review.

An improved model for the examination of biological effects of locally administered cytokines

Cytokines incorporated into agarose blocks and implanted subcutaneously into mice establish an in vivo gradient which can be used to mimic a local inflammatory process. We have developed a model in which cellular influx into cytokine impregnated blocks parallels the normal cellular reaction to infections or wounds. Agarose blocks containing supernatants from ConA activated rat spleen cells attracted neutrophils within 4 h. These cells were followed by lymphocytes and macrophages in 24 h. Flow cytometry analysis of lymphoid cells on day 1 revealed that 38% were Ig+ (B cell marker), 60% MAC-2,3+ and 20% Thy 1.2+ of which only a small fraction were expressing CD4 on their surface. These numbers changed with time following implantation of the blocks. Initially, isolated adherent cells (macrophages) were resting, with low phagocytic activity. Cells isolated from blocks at later time points were activated, as evidenced by their increased ability to ingest fluoresceinated beads. The secretion patterns of cells trafficking to murine rIL-1 containing agarose blocks were examined. TNF, IL-6 and antibody secreting cells were found. No IL-2 was detected at any time. We believe that this model will be of value in studies of local actions of cytokines.

Molecular heterogeneity of a Graves' thyroid-infiltrating T cell population rich in CD8+ and gamma delta+ T cells

We report here on the isolation and repertoire characterization of a Graves' thyroid T cell population which, unlike most Graves' thyroid T cell isolates reported before, was rich in CD4-CD8- T cells (16%, all TcR gamma delta+) and CD8+ T cells (75%) [TcR alpha beta+ (59%) and TcR gamma delta+ (16%)]. Only 7% of the isolated T cells were CD4+. By contrast, < 2% of peripheral blood mononuclear cells from the same patient were gamma delta+ and < 14% were CD8+. Sequence analysis of 18 TcR delta cDNAs prepared from these cells indicated the presence of at least 17 different gamma delta+ T cell clonotypes with molecularly heterogeneous antigen-binding site sequences. As opposed to most peripheral blood gamma delta+ T cells (express V delta 2 TcRs), 13 of the 17 different TcR delta clonotypes used a V delta 1 gene, although PCR amplification of TcR gamma- and TcR delta-specific cDNAs with V delta- and V gamma-gene family-specific oligonucleotides confirmed usage of all 4 V gamma and all 6 V delta families. Sequence analysis of 21 TcR alpha cDNAs from a TcR alpha-specific cDNA library indicated the presence of at least 12 different clonotypes, using 8 different V alpha gene families and heterogeneous antigen-binding site sequences. These results are in contrast with the selective V alpha gene usage reported for other intrathyroidal T cell subpopulations in autoimmune thyroid disease.