Endothelial cells augment the expression of CD40 ligand on newly activated human CD4+ T cells through a CD2/LFA-3 signaling pathway

Cluster of differentiation antigens: essential roles in the identification of teleost fish T lymphocytes

Cluster of differentiation (CD) antigens are cell surface molecules expressed on leukocytes and other cells associated with the immune system. Antibodies that react with CD antigens are known to be one of the most essential tools for identifying leukocyte subpopulations. T lymphocytes, as an important population of leukocytes, play essential roles in the adaptive immune system. Many of the CD antigens expressed on T lymphocytes are used as surface markers for T lymphocyte classification, including CD3, CD4 and CD8 molecules. In this review, we summarize the recent advances in the identification of CD molecules on T lymphocytes in teleosts, with emphasis on the functions of CD markers in the classification of T lymphocyte subsets. We notice that genes encoding CD3, co-receptors CD4 and CD8 have been cloned in several fish species and antibodies have been developed to study protein expression in morphological and functional contexts. T lymphocytes can be divided into CD4⁺ and CD8⁺ cells discriminated by the expression of CD4 and CD8 molecules in teleost, which are functionally similar to mammalian helper T cells (Th) and cytotoxic T cells (Tc), respectively. Further studies are still needed on the particular characteristics of teleost T cell repertoires and adaptive responses, and results will facilitate the health management and development of vaccines for fish.

African Swine Fever Virus CD2v Protein Induces β-Interferon Expression and Apoptosis in Swine Peripheral Blood Mononuclear Cells

African swine fever (ASF) is a hemorrhagic disease of swine characterized by massive lymphocyte depletion in lymphoid tissues due to the apoptosis of B and T cells, a process likely triggered by factors released or secreted by infected macrophages. ASFV CD2v (EP402R) has been implicated in viral virulence and immunomodulation in vitro; however, its actual function(s) remains unknown. We found that CD2v expression in swine PK15 cells induces NF-κB-dependent IFN-β and ISGs transcription and an antiviral state. Similar results were observed for CD2v protein treated swine PBMCs and macrophages, the major ASFV target cell. Notably, treatment of swine PBMCs and macrophages with CD2v protein induced apoptosis. Immunoprecipitation and colocalization studies revealed that CD2v interacts with CD58, the natural host CD2 ligand. Additionally, CD58 knockdown in cells or treatment of cells with an NF-κB inhibitor significantly reduced CD2v-mediated NF-κB activation and IFN-β induction. Further, antibodies directed against CD2v inhibited CD2v-induced NF-κB activation and IFN-β transcription in cells. Overall, results indicate that ASFV CD2v activates NF-κB, which induces IFN signaling and apoptosis in swine lymphocytes/macrophages. We propose that CD2v released from infected macrophages may be a significant factor in lymphocyte apoptosis observed in lymphoid tissue during ASFV infection in pigs.

CD58 Immunobiology at a Glance

The glycoprotein CD58, also known as lymphocyte-function antigen 3 (LFA-3), is a costimulatory receptor distributed on a broad range of human tissue cells. Its natural ligand CD2 is primarily expressed on the surface of T/NK cells. The CD2-CD58 interaction is an important component of the immunological synapse (IS) that induces activation and proliferation of T/NK cells and triggers a series of intracellular signaling in T/NK cells and target cells, respectively, in addition to promoting cell adhesion and recognition. Furthermore, a soluble form of CD58 (sCD58) is also present in cellular supernatant in vitro and in local tissues in vivo. The sCD58 is involved in T/NK cell-mediated immune responses as an immunosuppressive factor by affecting CD2-CD58 interaction. Altered accumulation of sCD58 may lead to immunosuppression of T/NK cells in the tumor microenvironment, allowing sCD58 as a novel immunotherapeutic target. Recently, the crucial roles of costimulatory molecule CD58 in immunomodulation seem to be reattracting the interests of investigators. In particular, the CD2-CD58 interaction is involved in the regulation of antiviral responses, inflammatory responses in autoimmune diseases, immune rejection of transplantation, and immune evasion of tumor cells. In this review, we provide a comprehensive summary of CD58 immunobiology.

Composite tissue allotransplantation: opportunities and challenges

Vascularized composite allotransplants (VCAs) have unique properties because of diverse tissue components transplanted en mass as a single unit. In addition to surgery, this type of transplant also faces enormous immunological challenges that demand a detailed analysis of all aspects of alloimmune responses, organ preservation, and injury, as well as the immunogenicity of various tissues within the VCA grafts to further improve graft and patient outcomes. Moreover, the side effects of long-term immunosuppression for VCA patients need to be carefully balanced with the potential benefit of a non-life-saving procedure. In this review article, we provide a comprehensive update on limb and face transplantation, with a specific emphasis on the alloimmune responses to VCA, established and novel immunosuppressive treatments, and patient outcomes.

Technical, Immunological, and Ethical Similarities and Differences Between Vascularized Composite Allotransplantation and Solid Organ Transplantation in Current Practice

Solid organ transplantation (SOT) is a surgical method used as the gold standard in end-term organ failure. Following SOT, successful results have also been achieved in vascularized composite tissue transplantation, which improves the quality of life with the success of solid organ transplants and the development of modern immunosuppressive regimens. This review discusses the preoperative, operative, postoperative, and immunological differences between vascularized tissue transplantation and SOT.

Costimulatory Function of Cd58/Cd2 Interaction in Adaptive Humoral Immunity in a Zebrafish Model

CD58 and CD2 have long been known as a pair of reciprocal adhesion molecules involved in the immune modulations of CD8⁺ T and NK-mediated cellular immunity in humans and several other mammals. However, the functional roles of CD58 and CD2 in CD4⁺ T-mediated adaptive humoral immunity remain poorly defined. Moreover, the current functional observations of CD58 and CD2 were mainly acquired from in vitro assays, and in vivo investigation is greatly limited due to the absence of a Cd58 homology in murine models. In this study, we identified cd58 and cd2 homologs from the model species zebrafish (Danio rerio). These two molecules share conserved structural features to their mammalian counterparts. Functionally, cd58 and cd2 were significantly upregulated on antigen-presenting cells and Cd4⁺ T cells upon antigen stimulation. Blockade or knockdown of Cd58 and Cd2 dramatically impaired the activation of antigen-specific Cd4⁺ T and mIgM⁺ B cells, followed by the inhibition of antibody production and host defense against bacterial infections. These results indicate that CD58/CD2 interaction was required for the full activation of CD4⁺ T-mediated adaptive humoral immunity. The interaction of Cd58 with Cd2 was confirmed by co-immunoprecipitation and functional competitive assays by introducing a soluble Cd2 protein. This study highlights a new costimulatory mechanism underlying the regulatory network of adaptive immunity and makes zebrafish an attractive model organism for the investigation of CD58/CD2-mediated immunology and disorders. It also provides a cross-species understanding of the evolutionary history of costimulatory signals from fish to mammals as a whole.

Isolation of luteal endothelial cells and functional interactions with T lymphocytes

The objectives of this study were to optimize the isolation of luteal endothelial cells (LEC) and examine their functional interactions with autologous T lymphocytes. Analysis by flow cytometry showed that the purity of LEC isolated by filtration was nearly 90% as indicated by Bandeiraea simplicifolia (BS)-1 lectin binding. LEC expressed mRNA for progesterone receptor (PGR), prostaglandin receptors (PTGFR, PTGER2 and 4, and PTGIR), tumor necrosis factor receptors (TNFRSF1A&B) and interleukin (IL) 1B receptors (IL1R1&2). LEC were pretreated with either vehicle, progesterone (P₄; 0-20 µM), prostaglandin (PG) E₂ or PGF_2α (0-0.2 µM), and further treated with or without TNF and IL1B (50 ng/mL each). LEC were then incubated with autologous T lymphocytes in an adhesion assay. Fewer lymphocytes adhered to LEC after exposure to high compared to low P₄ concentrations (cubic response; P < 0.05). In contrast, 0.2 µM PGE₂ and PGF_2α each increased T lymphocyte adhesion in the absence of cytokines (P < 0.05). LEC induced IL2 receptor alpha (CD25) expression and proliferation of T lymphocytes. In conclusion, filtration is an effective way of isolating large numbers of viable LEC. It is proposed that PGs and P₄ modulate the ability of endothelial cells to bind T lymphocytes, potentially regulating extravasation, and that LEC activate T lymphocytes migrating into or resident in the CL.

Vascularized composite allograft-specific characteristics of immune responses

Vascularized composite allograft (VCA) transplantation, or reconstructive transplantation, has revolutionized the treatment of complex tissue and functional defects. Despite arriving during an age in which the immunology of solid organ transplant rejection has been investigated in much detail, these transplants have offered new perspectives from which to explore the immunobiology of transplantation. VCAs have a number of unique molecular, cellular, and architectural features which alter the character and intensity of the rejection response. While much is yet to be clarified, an understanding of these distinct mechanisms affords new possibilities for the control of immune responses in an effort to improve outcomes after VCA transplantation.

Differential activation of human T cells to allogeneic endothelial cells, epithelial cells and fibroblasts in vitro

BACKGROUND

In the direct pathway, T cells recognize intact donor major histocompatability complexes and allogeneic peptide on the surface of donor antigen presenting cells (APCs). Indirect allorecognition results from the recognition of processed alloantigen by self MHC complexes on self APCs. In this study, we wished to evaluate the relative contribution of different intragraft cells to the alloactivation of nave and memory T cells though the direct and the indirect pathway of allorecognition.

METHODS

The processing of membrane fragments from IFN-treated single donor endothelial cells (EC), fibroblasts or renal epithelial cells (RPTEC) was evaluated by DiOC labeling of each cell type and flow cytometry following interaction with PBMC. Direct pathway activation of nave CD45RA+ or memory CD45RO+ CD4+ T cells was evaluated following coculture with IFN-treated and MHC class II-expressing EC, fibroblasts or RPTEC. Indirect pathway activation was assessed using CD45RA+ or CD45RO+ CD4+ T cells cocultured with autologous irradiated APCs in the absence or presence of sonicates derived from IFN-treated allogeneic EC, fibroblasts or RPTEC. Activation of T cells was assessed by [3H]thymidine incorporation and by ELISpot assays.

RESULTS

We find that CD14+ APCs readily acquire membrane fragments from fibroblasts and RPTEC, but fail to acquire membrane fragments from intact EC. However, APCs process membranes from EC undergoing apoptosis.There was a notable direct pathway alloproliferative response of CD45RO+ CD4+ T cells to IFN-treated EC, but not to fibroblasts or RPTEC. Also, there was a minimal direct pathway response of CD45RA+ CD4+ T cells to all cell types. In contrast, we found that both CD45RA+ and CD45RO+ CD4+ T cells proliferated following coculture with autologous APCs in the presence of sonicates derived from IFN-treated EC, fibroblasts or RPTEC. By ELISpot, we found that these T cells stimulated via the indirect pathway also produced the cytokines IFN, IL-2, IL-4 and IL-5.

CONCLUSIONS

Recipient APCs may readily process membrane fragments from allogeneic intragraft cells, but not from EC unless they are undergoing apoptosis. This processing is sufficient for indirect pathway alloactivation of both CD45RA+ and CD45RO+ CD4+ T cells. Only graft vascular EC mediate direct pathway reactivation of CD4+ T cells.

Post-transcriptional regulation in lymphocytes: the case of CD154

The control of mRNA decay is emerging as an important control point and a major contributor to gene expression in both immune and non-immune cells. The identification of protein factors and cis-acting elements responsible for transcript degradation has illuminated a comprehensive picture of precisely orchestrated events required to both regulate and establish the decay process. One gene that is highly regulated at the post-transcriptional level is CD40 ligand (CD154 or CD40L). CD154 on CD4(+) T cells is tightly controlled by an interacting network of transcriptional and post-transcriptional processes that result in precise surface levels of protein throughout an extended time course of antigen stimulation. The activation-induced stabilization of the CD154 transcript by a polypyrimidine tract-binding protein (PTB)-complex is a key event that corresponds to the temporal expression of CD154. In this review, we discuss known and potential roles of major mRNA decay pathways in lymphocytes and focus on the unique post-transcriptional mechanisms leading to CD154 expression by activated CD4(+) T cells.

Cognate interaction between endothelial cells and T cells

Endothelial cells lining the blood vessels form a barrier between circulating immune cells and parenchymal tissue. While the molecular mechanisms involved in antigen-independent recruitment of leukocytes into infected tissue have been extensively studied, the mechanisms involving antigen-specific recruitment of T cells into tissue have remained largely elusive. Here I shall review the experimental evidence that endothelial cells function as antigen-presenting cells and in this function contribute first to regulation of immune responses and second, to antigen-specific recruitment of T cells.

Human endothelial cells enhance human immunodeficiency virus type 1 replication in CD4+ T cells in a Nef-dependent manner in vitro and in vivo

Infected CD4+ T cells are the primary sites of human immunodeficiency virus type 1 (HIV-1) replication in vivo. However, signals from professional antigen-presenting cells (APCs), such as dendritic cells and macrophages, greatly enhance HIV-1 replication in T cells. Here, we report that in cocultures, vascular endothelial cells (ECs), which in humans can also serve as APCs, can enhance HIV-1 production of both CCR5- and CXCR4-utilizing strains approximately 50,000-fold. The observed HIV-1 replication enhancement conferred by ECs occurred only in memory CD4+ T cells, required expression of major histocompatibility complex class II (MHC-II) molecules by the ECs, and could not be conferred by fixed ECs, all of which are consistent with a requirement for EC-mediated T-cell activation via T-cell receptor (TCR) signaling. Deletion of nef (Nef-) decreased HIV-1 production by approximately 100-fold in T cells cocultured with ECs but had no effect on virus production in T cells cocultured with professional APCs or fibroblasts induced to express MHC-II. Human ECs do not express B7 costimulators, but Nef- replication in CD4(+)-T-cell and EC cocultures could not be rescued by anti-CD28 antibody. ECs act in trans to enhance wild-type but not Nef- replication and facilitate enhanced wild-type replication in naive T cells when added to T-cell or B-lymphoblastoid cell cocultures, suggesting that ECs also provide a TCR-independent signal to infected T cells. Consistent with these in vitro observations, wild-type HIV-1 replicated 30- to 50-fold more than Nef- in human T cells infiltrating allogeneic human skin grafts on human huPBL-SCID/bg mice, an in vivo model of T-cell activation by ECs. Our studies suggest that ECs, which line the entire cardiovascular system and are, per force, in frequent contact with memory CD4+ T cells, provide signals to HIV-1-infected CD4+ T cells to greatly enhance HIV-1 production in a Nef-dependent manner, a mechanism that could contribute to the development of AIDS.

T lymphocyte-endothelial cell interactions

Human vascular endothelial cells (EC) basally display class I and II MHC-peptide complexes on their surface and come in regular contact with circulating T cells. We propose that EC present microbial antigens to memory T cells as a mechanism of immune surveillance. Activated T cells, in turn, provide both soluble and contact-dependent signals to modulate normal EC functions, including formation and remodeling of blood vessels, regulation of blood flow, regulation of blood fluidity, maintenance of permselectivity, recruitment of inflammatory leukocytes, and antigen presentation leading to activation of T cells. T cell interactions with vascular EC are thus bidirectional and link the immune and circulatory systems.

CD154 transcriptional regulation in primary human CD4 T cells

CD154 (CD40-ligand) has a wide variety of pleiotropic effects throughout the immune system and is critical to both cellular and humoral immunity. Cell surface and soluble CD154 are primarily expressed by activated CD4 T cells. Expression of CD154 is tightly regulated in a time-dependent manner, and, like most T cell-derived cytokines and other members of the tumor necrosis factor (TNF) superfamily, CD154 is largely regulated at the level of gene transcription. Recently, dysregulated expression of CD154 has been noted in a number of autoimmune disorders, including systemic lupus erythematosus (SLE). In addition, abnormal expression of CD154 has been hypothesized to contribute to a wider array of diseases, from atherosclerosis to Alzheimer's disease. Until recently, very little was known about the transcriptional regulation of CD154. We are exploring CD154 regulation in primary human CD4 T cells in hopes of understanding the cis- and trans-regulatory elements that control its expression in the cells that normally express CD154. Ultimately, we hope to be able to correct abnormal expression of CD154 in various disease states and to help design gene therapy vectors for treating CD154-deficient individuals with hyper-IgM syndrome.

Atherosclerotic plaque formation and risk factors

Atherosclerosis (AT) is a progressive disease characterized by the accumulation of lipids, fibrous materials, and mineral in the arteries. Although many generalized or systemic risk factors predispose to its development, AT affect various regions of the circulation preferentially and yields distinct clinical manifestations depending on the particular circulatory bed affected. The progression of AT is currently believed to involve the interaction of endothelium, monocytes, and leukocytes, as well as the influences of cytokines, oxidized lipoproteins, hypertension, tobacco use, dyslipidemia, homocystinemia, and genetic determinants.

Endothelial cell and cAMP regulation of T-cell CD40 ligand: relevance of calcium/calmodulin-dependent kinase IV signalling

CD40 ligand (CD40L) expression is now recognized to contribute in the pathogenesis of vascular disease. Because increased CD40L has been associated with myocardial infarction, effects of endothelial cells and cAMP with respect to CD40L regulation may be of clinical relevance. In the present study, endothelial cells are shown to markedly increase CD40L on naïve CD4+ T cells with a more modest effect on memory T cells. Furthermore, the addition of dibutyryl cyclic AMP (dbcAMP) synergistically increased naïve cell CD40L but inhibited memory cell CD40L. Although it has previously been recognized that human endothelial cells can increase T-cell CD40L, this is the first description of the difference in responses of naïve and memory cells and the first demonstration of synergistic effects of endothelial cells and cAMP on CD40L regulation. Consistent with previous reports that CD40L regulation is distinctive, another marker of early activation (CD69) was not similarly regulated. The mechanisms of CD40L regulation were related to calcineurin and calcium/calmodulin dependent kinase IV (CaMKIV) signalling pathways. Endothelial cell costimulation of CD40L was found to be dependent upon calcineurin activity while cAMP actions to increase CD40L were dependent upon CaMKIV. Expression of a dominant negative CaMKIV construct further indicated an important role for CaMKIV in regulation of CD40L and cAMP responses. These data indicate that endothelial cell costimulation can interact with cAMP through calcium signalling pathways to synergistically enhance CD40L expression. Because increased CD40L is associated with atherosclerotic plaque and instability, results are relevant to the pathogenesis of atherosclerosis and myocardial infarction.

CD40-ligand in primate cardiac allograft and viral immunity

Our laboratory has studied the role of CD40 ligand (CD40L, CD154) in the primate immune response to allogenic and infectious challenges. We find that intensive early blockade of CD40L reliably attenuates acute rejection of primate cardiac allografts. Monotherapy fails to prevent late graft loss, which often occurs in association with rising antidonor antibody titers and allograft vasculopathy, despite continuing anti-CD40L therapy. In contrast, the primary humoral response to T helper dependent influenza viral antigen is inhibited during anti-CD40L therapy, and responses to subsequent immunization are blunted after discontinuation of therapy. These results are encouraging with regard to the tolerogenic potential of costimulatory blockade for specific T helper dependent antigens. However, these findings also indicate that pathogenic allograft responses in primates are probably not entirely CD40L-dependent. As such, additional immunomodulatory strategies are needed to facilitate tolerance to a transplanted organ.

Human endothelial cell presentation of antigen and the homing of memory/effector T cells to skin

Dermal microvascular endothelial cells (ECs) form a continuous lining that normally bars blood-borne T lymphocytes from entering the skin, but as part of the response to foreign antigen, dermal ECs undergo alterations in their surface proteins so as to provide signals to circulating T cells that lead to their activation and recruitment. Several observations suggest that human dermal microvascular ECs may help initiate cutaneous immune reactions by presentation of cognate antigens to circulating T memory cells: (1) antigen-specific inflammatory responses in the skin, as in other organs, involve accumulation of memory and effector T cell populations that are enriched in cells specific for the eliciting antigen; (2) recall responses to intradermal protein antigens in the skin start very rapidly within two hours of challenge; (3) dermal microvascular ECs in humans and other large mammals basally display high levels of class I and class II MHC molecules, the only known purpose of which is to present antigenic peptides to lymphocytes; (4) the lumen of dermal capillaries are narrower than the diameter of circulating T cells, ensuring surface contact; and (5) cultured human ECs effectively present antigens to resting memory T cells isolated from the circulation. Upon contact with activated T cells or their secreted products (cytokines), dermal ECs themselves become activated, increasing their capacity to recruit memory and effector T cell populations in an antigen-independent manner. Specifically, activated ECs express inducible leukocyte adhesion molecules such as E-selectin, ICAM-1, and VCAM-1; and several lines of evidence, including neutralizing antibody experiments and gene knockouts, have supported a role of these molecules in T cell recruitment. Dermal ECs have unique expression patterns of adhesion molecules that can determine the subsets of memory T cells that are recruited into the skin. For example, slow internalization of E-selectin allows more persistent expression of this protein on the surface of dermal ECs, favoring interactions with CLA-1+ T cells. VCAM-1 expression, normally confined to venular EC may extend to capillaries within the dermal papillae and contribute to epidermal inflammation, recruiting alpha4beta7 integrin-expressing T cells that also express the cadherin-binding integrin alphaEbeta7. New models involving transplantation of normal and genetically modified human dermal ECs into immunodeficient mice may be used to further explore these properties.

CD154 stimulation of interleukin-12 synthesis in human endothelial cells

The interaction of proinflammatory type 1 T helper (Th1) cells expressing the CD40 ligand (CD154) with endothelial cells expressing the corresponding receptor (CD40) may play an important role in chronic inflammation including arteriosclerosis. Here we demonstrate that activation of CD40 in human cultured endothelial cells (e.g. by interaction with freshly isolated human T cells) not only up-regulates expression of various adhesion molecules, chemokines and cytokines, but within 12-24 h also causes the release of bioactive interleukin-12 (IL-12 p70) through induction of IL-12 p40 synthesis. IL-12 p35, on the other hand, appears to be constitutively expressed in these cells. Despite enhancing expression of the other gene products, cytokines such as interferon-gamma (IFN-gamma) or tumor necrosis factor-alpha, alone or in combination, failed to induce IL-12 p40 expression, whereas IFN-gamma markedly augmented CD154-induced IL-12 p40 and p70 release. Of note was that the magnitude of CD154-induced IL-12 synthesis in the cultured endothelial cells was comparable to that evoked in freshly isolated human monocytes. This CD40-mediated induction of endothelial IL-12 synthesis may thus lead to an enhanced activation of the adherent CD154-expressing Th1 cells, thereby fuelling the proinflammatory response.

Cytoprotection of human umbilical vein endothelial cells against apoptosis and CTL-mediated lysis provided by caspase-resistant Bcl-2 without alterations in growth or activation responses

Graft endothelial cells are primary targets of host CTL-mediated injury in acute allograft rejection. As an in vitro trial of gene therapy to reduce CTL-mediated endothelial injury, we stably transduced early passage HUVEC with a caspase-resistant mutant form (D34A) of the anti-apoptotic gene Bcl-2. Bcl-2 transductants were compared with HUVEC transduced in parallel with an enhanced green fluorescent protein (EGFP) gene. Both transduced HUVEC have equivalent growth rates in complete medium and both show contact inhibition of growth. However, compared with EGFP-transduced HUVEC, the Bcl-2-transduced cells are resistant to the apoptotic effects of serum and growth factor withdrawal and are also resistant to the induction of apoptosis by staurosporine or by ceramide, with or without TNF. Transduced Bcl-2 did not reduce TNF-mediated NF-kappaB activation or constitutive expression of class I MHC molecules. HUVEC expressing D34A Bcl-2 were significantly more resistant to lysis by either class I-restricted alloreactive or PHA-redirected CTL than were HUVEC expressing EGFP. We conclude that transduction of graft endothelial cells with D34A Bcl-2 is a possible approach for reducing allograft rejection.

Antigen presentation by parenchymal cells: a route to peripheral tolerance?

T-cell activation and the development of efficient immune responses requires the delivery, by the antigen-presenting cell, of two distinct signals. The first results from the engagement of the TCR:CD3:CD4 complex, and the second from the interaction of CD28 with the B7 family of co-stimulatory molecules. In this context, the physiological significance and the functional consequences of antigen presentation by B7-deficient parenchymal cells, which express MHC class II molecules as a result of inflammation, remains a matter of debate. In this paper we have attempted to critically review the often conflicting reports on the functional effects of antigen presentation by epithelial and endothelial cells to T cells, both in vitro and in vivo. Our own findings are summarised in a model which is consistent with the suggestion of an important role for antigen presentation by parenchymal cells in the induction and the maintenance of peripheral tolerance.

Inhibition of T cell activation by normal human biliary epithelial cells

BACKGROUND/AIMS

Human intrahepatic biliary epithelial cells can express immune recognition elements and are targets for immune attack in several liver pathologies. The aim of this study was to investigate the ability of biliary epithelial cells to act as accessory cells for T cell activation in normal and inflammatory conditions.

METHODS

Normal biliary epithelial cells were cocultured with allogeneic unstimulated and mitogen- or antigen-stimulated peripheral blood lymphocytes. T cell responses were assessed by flow cytometry.

RESULTS

Biliary epithelial cells did not induce allostimulation in resting T cells and inhibited T cell activation in response to either phytohaemagglutinin, mitogenic anti-CD3 antibody or recall antigen, irrespective of the presence of accessory cells. Biliary epithelial cells did not affect T cell viability, promote or inhibit activation-induced apoptosis nor modulate expression of CD95/Fas. In presence of biliary epithelial cells, stimulated T cells failed to develop an antigen-committed (CD45R0hi) phenotype and were unresponsive to subsequent CD3 ligation. However, T cells underwent normal activation in the presence of biliary epithelial cells which had been pre-treated with Interferon gamma or TGFbeta, cytokines implicated in liver disease.

CONCLUSIONS

In normal liver, biliary epithelial cells inhibit rather than promote T cell activation, but their anergising effects may be overcome in response to trauma.

Immunobiology of human vascular endothelium

The author's laboratory studies interactions between human T lymphocytes and vascular endothelial cells (EC). Our work is organized around three hypotheses. First, we propose that vascular EC can initiate secondary (i.e., recall) immune reactions by presenting antigenic peptide-major histocompatibility complex (MHC) complexes to those circulating memory T cells whose cognate antigen is locally present within a peripheral tissue, e.g., as a consequence of infection or allogeneic transplantation. In this way, EC can increase the efficiency of immune surveillance. Second, we propose that T cell signals, both secreted (e.g., cytokines) and contact-dependent (e.g., CD40 ligand), activate new gene expression in EC that induce the capacity to perform new effector functions, such as leukocyte recruitment and activation or initiation of intravascular coagulation. In this way, EC can participate as effector cells for cell-mediated immune reactions. Third, we propose that EC are major targets of immune-mediated injury. Consequently, increasing resistance of endothelium to immune effector mechanisms may protect tissues from damage, e.g., in allograft rejection. These three hypotheses are explored through in vitro experiments, through analyses of human tissue specimens, and through in vivo studies employing novel human-mouse chimeric animals.

Human Endothelial Cells Augment Early CD40 Ligand Expression in Activated CD4+ T Cells Through LFA-3-Mediated Stabilization of mRNA

Human endothelial cells (EC) augment CD40 ligand (CD40L) expression on PHA-activated CD4+ T cells at early times (e.g., 4–6 h). Fixed EC, devoid of mRNA, are comparable to living EC in their capacity to augment early CD40L expression on CD4+ T cells. Fixed EC increase T cell mRNA expression of both IL-2 and CD40L compared with PHA alone at 6 h. EC are unable to increase the rate of transcription of CD40L compared with PHA alone as measured with a promoter-reporter gene, although they do increase transcription of an IL-2 promoter-reporter gene. Fixed EC prolong the half-life of CD40L mRNA &gt;2-fold. Inclusion of anti-human LFA-3 (CD58) mAb or pretreatment of EC with an LFA-3 antisense oligonucleotide blocks EC-induced increases in CD40L expression, whereas mAb to ICAM-1 or pretreatment with ICAM-1 antisense oligonucleotide does not. Moreover, mAb to LFA-3 reverses the capacity of EC to prolong the half-life of CD40L mRNA, whereas mAb to ICAM-1, even in combination with mAb to ICAM-2, does not. We conclude that EC use LFA-3 to increase early CD40L protein expression on newly activated CD4+ T cells by stabilizing CD40L mRNA.

The immunobiology of bile and biliary epithelium

Long thought to be just a simple pipe involved in the delivery of bile from hepatocytes to the gallbladder and intestine, bile ducts are now regarded as highly dynamic structures consisting of cell populations involved in formation, transport and modification of bile by both secretory and absorptive processes. In fact, both bile and biliary epithelium appear to have active immunologic roles in both innate and adaptive immune responses. These roles are becoming increasingly clear as techniques have been developed allowing for the study of bile and biliary epithelial cells (BECs) in mucosal immunity. Bile is actively involved in the transport of immunoglobulin to the intestine, while BECs secrete chemokines and cytokines and serve to localize the immune response by expressing critical cell adhesion molecules. Evidence suggests that BECs may also function as professional antigen-presenting cells (APC) and, in the process, contribute to the modulation of inflammatory reactions. Bile ducts and, in particular, BECs, are the primary site of damage in several immunologically mediated liver diseases. Progress in these important areas has been rapid and forms the basis of this review.

Cytokine-inducible CD40 gene expression in vascular smooth muscle cells is mediated by nuclear factor kappaB and signal transducer and activation of transcription-1

The interaction of T-lymphocytes expressing the CD40 ligand (CD154) and cells of the vessel wall expressing the corresponding receptor protein (CD40) may play an important role in chronic inflammation including arteriosclerosis. One way of interfering with CD40-CD154 signalling is to prevent CD40 expression, the regulation of which, however, has yet to be elucidated. Therefore, we studied CD40 expression in rat aortic cultured smooth muscle cells. Both CD40 mRNA and protein expression in these cells was markedly enhanced as early as 6 h after exposure to different pro-inflammatory cytokines. Experiments with actinomycin D and subsequent run-on analyses revealed that CD40 expression in response to these cytokines was regulated at the level of transcription. Moreover, electrophoretic mobility shift analyses along with the employment of transcription factor decoy oligodeoxynucleotides demonstrated that tumor necrosis factor alpha via nuclear kappaB and interferon-gamma via signal transducer and activator of transcription-1 up-regulate CD40 gene expression in rat aortic cultured smooth muscle cells.

Induction of anti-tumor immunity elicited by tumor cells expressing a murine LFA-3 analog via a recombinant vaccinia virus

T cell activation requires binding of the T cell receptor to the major histocompatibility molecule-peptide complex in the presence of adhesion and/or costimulatory molecules such as B7-1 (CD80), B7-2 (CD86), ICAM-1 (CD54), and LFA-3 [corrected]. The major ligand of CD2 is CD48, the murine analog of human leukocyte function-associated antigen 3 (LFA-3). To determine the effect of LFA-3 expression on the immunogenicity of tumor cells, we constructed a recombinant vaccinia virus containing the murine LFA-3 gene (designated rV-LFA-3). rV-LFA-3 was shown to be functional in vitro in terms of expression of LFA-3, T cell proliferation, adhesion, and cytotoxicity. Subcutaneous inoculation of rV-LFA-3-infected murine colon adenocarcinoma tumor cells (MC38) into immunocompetent syngeneic C57BL/6 mice resulted in complete lack of tumor growth. Inoculation of MC38 cells infected with equal doses of control wild-type vaccinia virus resulted in tumor growth in all animals. In addition, partial immunological protection was demonstrated against subsequent challenge with uninfected parental tumor cells up to 56 days after vaccination with rV-LFA-3-infected cells. Anti-tumor memory was also demonstrated by using gamma-irradiated MC38 cells and cells from another carcinoma model (CT26). These studies demonstrate that expression of LFA-3 via a poxvirus vector can be used to induce anti-tumor immunity.

TNF-alpha, not CD154 (CD40L), plays a major role in SEB-dependent, CD4(+) T cell-induced endothelial cell activation in vitro

CD4(+) T cell effector molecules, in particular TNF-alpha and CD154, activate endothelial cells. However, the relative contributions of TNF-alpha and CD154 in mediating endothelial cell activation during complex Ag-driven CD4(+) T cell-endothelial cell interactions are not known. We utilized an in vitro model of CD4(+) T cell-endothelial cell interactions to characterize the contributions of TNF-alpha and CD154 in mediating upregulation of adhesion molecules CD54, CD62E, and CD106 on human umbilical vein endothelial cells (HUVEC). HUVEC were first treated with IFN-gamma to upregulate MHC Class II expression. IFN-gamma minimally effects HUVEC adhesion molecule expression but renders them capable of MHC class II restricted interactions with CD4(+) T cells. Coculturing MHC class II+ HUVEC and CD4(+) T cells with the superantigen SEB induces a rapid and marked upregulation of CD54, CD62E, and CD106 expression on HUVEC, as shown by FACS analysis. To study the effector molecules mediating SEB-driven, CD4(+) T cell-dependent endothelial cell activation, similar experiments were performed in the presence of neutralizing anti-CD154, anti-TNF-alpha, or anti-IL1 antibodies, as well as combinations of these antibodies. In contrast to the anti-CD154 or anti-IL-1 antibodies, the anti-TNF-alpha mAb markedly inhibited SEB-dependent, CD4(+) T cell-induced HUVEC activation. We conclude that TNF-alpha, not CD154, plays the major role in SEB-driven, CD4(+) T cell-induced endothelial cell activation in vitro.

Expression and cytokine regulation of immune recognition elements by normal human biliary epithelial and established liver cell lines in vitro

BACKGROUND/AIMS

Biliary epithelial cells are targets of immune-mediated attack in conditions such as primary biliary cirrhosis and allograft rejection. This has been attributed to the ability of biliary epithelial cells to express ligands for T cell receptors. We aimed to investigate the expression of immune recognition elements and the effects of pro-inflammatory and anti-inflammatory cytokines on cell surface phenotypes of normal human biliary epithelial cells and established human liver-derived (PLC/PRF/5, HepG2, Hep3B and CC-SW) lines.

METHODS

Cells were cultured in the presence or absence of cytokines for 72 h, and expression of cell surface molecules was assessed by flow cytometry and immunofluorescence.

RESULTS

All cell lines expressed MHC class I, ICAM-1 (CD54), LFA-3 (CD58) and EGF receptor, and all but Hep3B expressed Fas/Apo-1 (CD95). Unlike hepatocyte-derived cell lines, biliary epithelial cells and CC-SW expressed CD40 and CD44. As expected, IFNgamma and TNFalpha upregulated expression of ICAM-1, MHC class I and MHC class II, particularly in biliary epithelial cells. TGFbeta downregulated these molecules and downregulated CD95 on biliary epithelial cells, but upregulated LFA-3. The Th2 cytokines had little effect, although IL-4 upregulated CD95 expression on biliary epithelial cells. IFNgamma upregulated CD40 expression on biliary epithelial cells, CC-SW and HepG2.

CONCLUSIONS

These findings imply that biliary epithelial cells may be capable of interacting with activated T lymphocytes via CD40 and LFA-3, which are thought to be important T cell accessory ligands for T cell activation in a B7-independent manner. Sensitivity to pro-inflammatory cytokines and expression of CD95 may explain why biliary epithelial cells are primary targets for autoimmune attack.

Interactions between T lymphocytes and endothelial cells in allograft rejection

Vascular endothelial cells participate in the process of allograft rejection by promoting both the recruitment and the activation of alloreactive T cells. There have been three major recent advances in the field of interactions between T cells and endothelial cells that are of direct relevance to the process of cell-mediated responses to allografts: first, endothelial cells mediate selective recruitment of CD4+ T cell subsets, including naive and memory T cells and T cell subsets of the Th1 and Th2 phenotypes; second, endothelial cells co-stimulate the production of effector cytokines by helper T cells; and third, endothelial cells regulate T cell apoptosis.

Differential immunosuppressive activity of monoclonal CD2 antibodies on allograft rejection versus specific antibody production

CD2 is a co-stimulatory receptor involved in T cell activation. Here we report on immunosuppressive effects of three mouse CD2 monoclonal antibodies (OX34, OX54, OX55) directed against non-overlapping epitopes of the rat CD2 receptor on various modes of T cell activation in vitro and in vivo. Although non-ligand-blocking OX54 and OX55, in concert, activated T cells through CD2 in vitro, they individually suppressed the mixed lymphocyte reaction (MLR) and significantly prolonged allograft survival after rat heart transplantation in vivo. Phenotype analysis revealed that OX55 significantly down-modulated CD2 in vivo, whereas OX54 depleted T cells. Graft rejection coincided with re-expression of CD2 and clearance of OX55 from serum, whereas T cell depletion by OX54 outlasted the period of graft survival. The most suppressive antibody, OX34, down-modulated CD2 and inhibited T cell activation through the TCR or CD2 and the MLR and prolonged median allograft survival time from 7 days in controls to 45 days in the absence of any additional treatment. Graft survival was clearly dose dependent and correlated with the duration of CD2 down-modulation and the presence of circulating CD2 antibody in serum. Importantly, the specific antibody production to a T cell-dependent antigen as demonstrated by immunization with keyhole limpet hemocyanin in vivo remained unaffected after treatment with OX34. These results demonstrate the pivotal role of CD2 signaling in mediating allogeneic immune reactions after vascularized organ transplantation while allowing specific humoral immune responses in vivo.

Requirement of a second signal via protein kinase C or protein kinase A for maximal expression of CD40 ligand. Involvement of transcriptional and posttranscriptional mechanisms

High levels of CD40 ligand (CD40L) protein expression are induced on native T cells by increasing the intracellular Ca2+ concentration. In the present study we have shown that ionomycin induces CD40L gene transcription leading to mRNA accumulation which translates to high levels of protein expression. Conversely, agents which increase the intracellular levels of cyclic AMP (cAMP), such as prostaglandin E2 (PGE2) or dibutyryl cyclic AMP (dbcAMP), were unable to induce CD40L expression on T lymphocytes. Cell activation by phorbol 12-myristate 13-acetate (PMA) treatment had a slight effect on increasing CD40L mRNA and protein levels. However, PMA and dbcAMP synergized with ionomycin to significantly increase and to prolong the CD40L expression. Nuclear run-on assays revealed that PMA, but not dbcAMP, increased threefold the CD40L gene transcription rate induced by ionomycin. This effect was independent of de novo protein synthesis. In addition, at a posttranscriptional level, both reagents synergized with the Ca2+ ionophore to prolong the CD40L mRNA half-life by a mechanism which was also independent of de novo protein synthesis. Moreover, when transcription was blocked with actinomycin D, an increment of the CD40L transcript levels induced by PMA or dbcAMP on ionomycin-treated cells was observed in the presence of cycloheximide. This probably means that newly synthesized protein may contribute to the CD40L mRNA destabilization. In summary, these data show that PMA and dbcAMP synergized with ionomycin to increase the CD40L mRNA and protein levels. The up-regulatory effect of PMA was accomplished at a transcriptional and posttranscriptional level, whereas dbcAMP exerted its synergistic effect exclusively at a posttranscriptional level.

CD40/CD40 ligand interactions in normal, reactive and malignant lympho-hematopoietic tissues

CD40 is a 48 Kd integral membrane protein expressed by cells of B cells, origin, dentritic cells, monocytes, epithelial cells, endothelial cells and tumor cells including carcinomas, B cell lymphomas/leukemias and Hodgkin and Reed-Sternberg (HRS) cells of Hodgkin's disease (HD). CD40 has been clustered as a member of the nerve growth factor (NGF)/tumor necrosis factor (TNF) receptor superfamily with the corresponding counterstructure, the CD40 ligand (L) being mainly expressed by activated CD4+ T cells, but also some activated CD8+ T cells, basophils, eosinophils, mast cells and stromal cells. CD40L shares significant amino acid homology with TNF particularly in its extracellular domain ("TNF homology region") and is therefore viewed as a member of the TNF ligand superfamily. Binding of CD40L+ T cells to CD40+ B cells is thought to play a major role in T cell-dependent B cell activation, B cell proliferation, Ig isotype switching, memory B cell formation and rescue of B cells from apoptotic death in germinal centers. Mutations of the CD40L gene have been associated with the X-linked hyper-IgM immunodeficiency syndrome, pointing to the critical role of the CD40/CD40L interaction in the T cell-B cell interplay. Accordingly, expression of CD40 by human lympho-hematopoietic tumors has been shown in most of the B cell neoplasias, H-RS cells and HD and some carcinomas. In contrast, CD40L+ tumor cells are almost invariably restricted to CD4+/CD8- T cell lymphomas. Overall, functional CD40/CD40L interactions appear to be critical for cellular activation signals during immune responses and neoplastic tumor cell growth. The understanding of the biology of CD40L has improved our diagnostic and therapeutic repertoire in the management of several human diseases, including CD40+ tumors.

Increased interleukin 12 production in progressive multiple sclerosis: induction by activated CD4+ T cells via CD40 ligand

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system postulated to be a cell-mediated autoimmune disease in which interferon gamma (IFN-gamma) plays an important role. There is increased IFN-gamma secretion in MS, and IFN-gamma administration induces exacerbations of disease. We found that interleukin 12 (IL-12) was responsible for raised IFN-gamma secretion in MS as anti-IL-12 antibodies reversed raised anti-CD3-induced IFN-gamma in MS patients to normal levels. Furthermore, we found a marked increase in T cell receptor-mediated IL-12 secretion in progressive MS patients vs. controls (24.8 +/- 7.7 pg/ml vs. 1.5 +/- 1.0 pg/ml, P = 0.003) and vs. relapsing-remitting patients (3.7 +/- 1.4 pg/ml, P < 0.05). Investigation of the cellular basis for raised IL-12 demonstrated that T cells from MS patients induced IL-12 secretion from non-T cells, and that T cells from MS patients could even drive non-T cells from normal subjects to produce increased IL-12. Anti-CD40 ligand antibody completely blocked IL-12 secretion induced by activated T cells, and we found increased CD40 ligand expression by activated CD4+ T cells in MS patients vs. controls. The CD40 ligand-dependent Th1-type immune activation was observed in the progressive but not in the relapsing-remitting from of MS, suggesting a link to disease pathogenesis and progression and providing a basis for immune intervention in the disease.