EB病毒潜伏膜蛋白1基因对上皮细胞增殖的影响

为了研究ＥＢ病毒潜伏膜蛋白１（ＬＭＰ１）基因对上皮细胞增殖的影响,探索ＬＭＰ１在上皮细胞肿瘤发生中所起的作用。用ＬＭＰ１基因真核表达质粒转染人胚肾上皮细胞,检测了转染细胞中ＬＭＰ１的表达,观察细胞在软琼脂中的集落形成能力、ＭＴＴ吸收能力以及ＰＣＮＡ的表达情况。结果显示,被ＬＭＰ１基因转染的细胞生长旺盛,能在软琼脂中形成多个集落,ＭＴＴ吸收能力增强,ＰＣＮＡ的表达水平增高。因此认为ＬＭＰ１基因能明显改变上皮细胞的生物学行为,促进细胞的生长、增殖和转化,使转染的上皮细胞获得肿瘤细胞的生长特征     

Regulatory T cells dynamically control the primary immune response to foreign antigen

The population dynamics that enable a small number of regulatory T (T(R)) cells to control the immune responses to foreign Ags by the much larger conventional T cell subset were investigated. During the primary immune response, the expansion and contraction of conventional and T(R) cells occurred in synchrony. Importantly, the relative accumulation of T(R) cells at peak response significantly exceeded that of conventional T cells, reflecting extensive cell division within the T(R) cell pool. Transfer of a polyclonal T(R) cell population before immunization antagonized both polyclonal and TCR transgenic responses, whereas blocking T(R) cell function enhanced those responses. These results define an inverse quantitative relationship between T(R) and conventional T cells that controls the magnitude of the primary immune response. The high frequency of dividing T(R) cells suggests degenerate TCR specificity enabling activation by a broad spectrum of Ags.     

The latent membrane protein 1 of Epstein-Barr virus (EBV) primes EBV latency cells for type I interferon production

Epstein-Barr virus (EBV) latency has been associated with a variety of human cancers. Latent membrane protein 1 (LMP-1) is one of the key viral proteins required for transformation of primary B cells in vitro and establishment of EBV latency. We have previously shown that LMP-1 induces the expression of several interferon (IFN)-stimulated genes and has antiviral effect (Zhang, J., Das, S. C., Kotalik, C., Pattnaik, A. K., and Zhang, L. (2004) J. Biol. Chem. 279, 46335-46342). In this report, a novel mechanism related to the antiviral effect of LMP-1 is identified. We show that EBV type III latency cells, in which LMP-1 is expressed, are primed to produce robust levels of endogenous IFNs upon infection of Sendai virus. The priming action is due to the expression of LMP-1 but not EBV nuclear antigen 2 (EBNA-2). The signaling events from the C-terminal activator regions of LMP-1 are essential to prime cells for high IFN production. LMP-1-mediated activation of NF-kappaB is apparently necessary and sufficient for LMP-1-mediated priming effect in DG75 cells, a human B cell line. IFN regulatory factor 7 (IRF-7) that can be activated by LMP-1 is also implicated in the priming action. Taken together, these data strongly suggest that LMP-1 may prime EBV latency cells for IFN production and that the antiviral property of LMP-1 may be an intrinsic part of EBV latency program, which may assist the establishment and/or maintenance of viral latency.     

PRA1 promotes the intracellular trafficking and NF-kappaB signaling of EBV latent membrane protein 1

Latent membrane protein 1 (LMP1), which is an Epstein-Barr virus (EBV)-encoded oncoprotein, induces nuclear factor-kappa B (NF-kappaB) signaling by mimicking the tumor necrosis factor receptor (TNFR). LMP1 signals primarily from intracellular compartments in a ligand-independent manner. Here, we identify a new LMP1-interacting molecule, prenylated Rab acceptor 1 (PRA1), which interacts with LMP1 for the first time through LMP1's transmembrane domain, and show that PRA1 is involved in intracellular LMP1 trafficking and LMP1-induced NF-kappaB activity. Immunofluorescence and biochemical analyses revealed that LMP1 physically interacted with PRA1 at the Golgi apparatus, and the colocalization of LMP1 and PRA1 to the Golgi was sensitive to nocodazole and brefeldin A. Coexpression of a PRA1 export mutant or knockdown of PRA1 led to redistribution of LMP1 and its associated signaling molecules to the endoplasmic reticulum and subsequent impairment of LMP1-induced NF-kappaB activation, but had no effect on CD40- and TNFR1-mediated signaling or the functional integrity of the Golgi apparatus. These novel findings provide important new insights into LMP1, and identify an unexpected new role for PRA1 in cellular signaling.     

Antigen-specific T cells transduced with IL-10 ameliorate experimentally induced arthritis without impairing the systemic immune response to the antigen

For the treatment of rheumatoid arthritis, efficient drug delivery methods to the inflamed joints need to be developed. Because T cells expressing an appropriate autoantigen-specific receptor can migrate to inflamed lesions, it has been reasoned that they can be employed to deliver therapeutic agents. To examine the ability and efficiency of such T cells as a vehicle, we employed an experimentally induced model of arthritis. Splenic T cells from DO11.10 TCR transgenic mice specific for OVA were transduced with murine IL-10. Adoptive transfer of the IL-10-transduced DO11.10 splenocytes ameliorated OVA-induced arthritis despite the presence of around 95% nontransduced cells. Using green fluorescent protein as a marker for selection, the number of transferred cells needed to ameliorate the disease was able to be reduced to 10(4). Preferential accumulation of the transferred T cells was observed in the inflamed joint, and the improvement in the disease was not accompanied by impairment of the systemic immune response to the Ag, suggesting that the transferred T cells exert their anti-inflammatory task locally, mainly in the joints where the Ag exists. In addition, IL-10-transduced DO11.10 T cells ameliorated methylated BSA-induced arthritis when the arthritic joint was coinjected with OVA in addition to methylated BSA. These results suggest that T cells specific for a joint-specific Ag would be useful as a therapeutic vehicle in rheumatoid arthritis for which the arthritic autoantigen is still unknown.     

Regulatory T cells and immune tolerance

Regulatory T cells (Tregs) play an indispensable role in maintaining immunological unresponsiveness to self-antigens and in suppressing excessive immune responses deleterious to the host. Tregs are produced in the thymus as a functionally mature subpopulation of T cells and can also be induced from naive T cells in the periphery. Recent research reveals the cellular and molecular basis of Treg development and function and implicates dysregulation of Tregs in immunological disease.     

Autoantigen-specific IL-10-transduced T cells suppress chronic arthritis by promoting the endogenous regulatory IL-10 response

Deficient T cell regulation can be mechanistically associated with development of chronic autoimmune diseases. Therefore, combining the regulatory properties of IL-10 and the specificity of autoreactive CD4(+) T cells through adoptive cellular gene transfer of IL-10 via autoantigen-specific CD4(+) T cells seems an attractive approach to correct such deficient T cell regulation that avoids the risks of nonspecific immunosuppressive drugs. In this study, we studied how cartilage proteoglycan-specific CD4(+) T cells transduced with an active IL-10 gene (T(IL-10)) may contribute to the amelioration of chronic and progressive proteoglycan-induced arthritis in BALB/c mice. TCR-transgenic proteoglycan-specific T(IL-10) cells ameliorated arthritis, whereas T(IL-10) cells with specificity for OVA had no effect, showing the impact of Ag-specific targeting of inflammation. Furthermore, proteoglycan-specific T(IL-10) cells suppressed autoreactive proinflammatory T and B cells, as T(IL-10) cells caused a reduced expression of IL-2, TNF-alpha, and IL-17 and a diminished proteoglycan-specific IgG2a Ab response. Moreover, proteoglycan-specific T(IL-10) cells promoted IL-10 expression in recipients but did not ameliorate arthritis in IL-10-deficient mice, indicating that T(IL-10) cells suppress inflammation by propagating the endogenous regulatory IL-10 response in treated recipients. This is the first demonstration that such targeted suppression of proinflammatory lymphocyte responses in chronic autoimmunity by IL-10-transduced T cells specific for a natural Ag can occur via the endogenous regulatory IL-10 response.     

Proinflammatory cytokines dominate the early immune response to filarial parasites

Although the early human immune response to the infective-stage larvae (L3) of Brugia malayi has not been well-characterized in vivo (because of the inability to determine the precise time of infection), the consensus has been that it must involve a predominant Th2 environment. We have set up an in vitro system to study this early immune response by culturing PBMC from unexposed individuals with live L3 of B. malayi. After 24 h of culture, T cell responses were examined by flow cytometry and by quantitative real-time RT-PCR for multiple cytokines. T cells were activated early following exposure to L3 as indicated by up-regulation of surface markers CD69 and CD71. The frequency of T cells expressing proinflammatory Th1 cytokines (IFN-gamma, TNF-alpha, GM-CSF, IL-1alpha, and IL-8) but not Th2 cytokines (IL-4, IL-5, IL-6, IL-10, and IL-13) was significantly increased in response to L3. This T cell response occurred in both the CD4 and CD8 T cell compartment and was restricted to the effector/memory pool (CD45RO(+)). This T cell response was not due to LPS activity from the parasite or from its endosymbiont, Wolbachia; moreover, it required the presence of APC as well as direct contact with live L3. Real-time RT-PCR analysis of multiple cytokines in the T cells confirmed the increased expression of proinflammatory Th1 cytokines. Up-regulation of these cytokines suggests that the primary immune response to the live infective stage of the parasite is not predominantly Th2 in nature but rather dominated by a proinflammatory response.     

Regulatory T cells and IL-10 independently counterregulate cytotoxic T lymphocyte responses induced by transcutaneous immunization

Background

The imidazoquinoline derivate imiquimod induces inflammatory responses and protection against transplanted tumors when applied to the skin in combination with a cognate peptide epitope (transcutaneous immunization, TCI). Here we investigated the role of regulatory T cells (T_reg) and the suppressive cytokine IL-10 in restricting TCI-induced cytotoxic T lymphocyte (CTL) responses.

Methodology/Principal Findings

TCI was performed with an ointment containing the TLR7 agonist imiquimod and a CTL epitope was applied to the depilated back skin of C57BL/6 mice. Using specific antibodies and FoxP3-diphteria toxin receptor transgenic (DEREG) mice, we interrogated inhibiting factors after TCI: by depleting FoxP3⁺ regulatory T cells we found that specific CTL-responses were greatly enhanced. Beyond this, in IL-10 deficient (IL-10^-/-) mice or after blocking of IL-10 signalling with an IL-10 receptor specific antibody, the TCI induced CTL response is greatly enhanced indicating an important role for this cytokine in TCI. However, by transfer of T_reg in IL-10^-/- mice and the use of B cell deficient JHT^-/- mice, we can exclude T_reg and B cells as source of IL-10 in the setting of TCI.

Conclusion/Significance

We identify T_reg and IL-10 as two important and independently acting suppressors of CTL-responses induced by transcutaneous immunization. Advanced vaccination strategies inhibiting T_reg function and IL-10 release may lead the development of effective vaccination protocols aiming at the induction of T cell responses suitable for the prophylaxis or treatment of persistent infections or tumors.     

Analysis of cellular immune response to EBV by using cloned T cell lines

Eight cloned T cell lines specific for Epstein Barr virus-transformed B lymphocytes were derived. In the presence of the autologous virus-infected B cells, the T cell lines show HLA-restricted cytotoxic activity and also secrete alpha-interferon in sufficient amounts to inhibit infection and transformation. Four of these clones showed restriction to a single HLA locus (two for A3, and two for B7) and three showed exquisite self-restriction lysing only autologous targets. These seven clones expressed the classical cell surface phenotype of cytotoxic T cells being T3, 8, 11, and la-positive and T4-negative. An eighth clone that lacked the T8 surface marker appeared to recognize both B7 and BW51. HLA restriction was confirmed: 1) by the ability of a monoclonal antibody against an HLA-A,B,C framework antigen (W6-32) to block the cytotoxicity; 2) the failure of the clones to lyse Daudi, an EBV-positive, HLA-A,B, C-negative cell line; and 3) successful competition of the cytotoxicity by autologous but not allogeneic cold targets. The cloned T cells do not kill EBV-negative targets such as autologous pokeweed mitogen blasts and cell lines including CEM and the natural killer cell target K562. The results suggest T cell clones may be generated against an EBV-associated membrane antigen on transformed B cells, perhaps equivalent to the lymphocyte-determined membrane antigen, and that the recognition is restricted by a single HLA determinant. We propose that single T cells can play multiple roles in controlling EBV infection in vitro and in vivo including the elimination of transformed cells by cytotoxicity and the prevention by secreted interferon of further re-infection and transformation.     

Regulatory T cells inhibit protein kinase C theta recruitment to the immune synapse of naive T cells with the same antigen specificity

The precise mechanisms by which regulatory T cells operate, particularly their effect on signaling pathways leading to T cell activation, are poorly understood. In this study we have used regulatory T (Treg) cells of known Ag specificity, generated in vivo, to address their effects on early activation events occurring in naive T cells of the same Ag specificity. We found that the Treg cells need to be present at the moment of priming to suppress activation and proliferation of the naive T cell. Furthermore, the Treg cells significantly inhibit the recruitment of protein kinase Ctheta (PKCtheta) to the immune synapse of the naive T cell as long as both T cells are of the same Ag specificity and are contacting the same APC. Finally, naturally occurring CD4(+)25(+) T cells seem to have the same effect on PKCtheta recruitment in CD25(-) T cells of the same Ag specificity. These results suggest that although additional mechanisms of regulation are likely to exist, inhibition of PKCtheta recruitment in the effector T cell may be a common regulatory pathway leading to the absence of NF-kappaB activation and contributing to the block of IL-2 secretion characteristic of immune suppression.     

Semi-mature IL-12 secreting dendritic cells present exogenous antigen to trigger cytolytic immune responses

Dendritic cells (DC) are candidates for antigen-presenting cells that present exogenous antigen on MHC class I molecules to cytotoxic T lymphocytes (CTL), a process referred to as cross-priming. We triggered interleukin (IL)-12 release from DC, which was limited to the first day after maturation induction, by a combination of lipopolysaccharide (LPS) and interferon (IFN)-. To stimulate T lymphocytes, we used soluble protein derived from lysis of Epstein-Barr virus (EBV)-transformed lymphoblastoid cell lines (LCL) or ovalbumin loaded onto DC. Co-culture was initiated 2–6 or 48 h after maturation corresponding to semi-mature actively IL-12-secreting type 1 DC (sm-DC1) or a fully mature DC1 that had lost the ability to release IL-12 (fm-DC1), respectively. IL-12-secreting sm-DC1 but not fm-DC1 efficiently triggered cytolytic activity in autologous T lymphocytes. The combination of IL-1, IL-6, TNF-, and prostaglandin E2 generated type 2 DC that did not secrete IL-12 (DC2) and could not prime T-cell cytolytic activity. However, supplementation of cultures using DC2 with IL-12 resulted in CTL activity while the presence of anti-IL-12 monoclonal antibodies in cultures using IL-12 secreting sm-DC1 suppressed CTL activity. Thus, actively IL-12-secreting sm-DC1 are necessary and sufficient for the antigen-specific expansion of CTL in response to exogenously provided soluble antigen.     

Inhibition of latent membrane protein 1 impairs the growth and tumorigenesis of latency II Epstein-Barr virus-transformed T cells

Epstein-Barr virus (EBV) is a common human herpesvirus. Infection with EBV is associated with several human malignancies in which the virus expresses a set of latent proteins, among which is latent membrane protein 1 (LMP1). LMP1 is able to transform numerous cell types and is considered the main oncogenic protein of EBV. The mechanism of action is based on mimicry of activated members of the tumor necrosis factor (TNF) receptor superfamily, through the ability of LMP1 to bind similar adapters and to activate signaling pathways. We previously generated two unique models: a monocytic cell line and a lymphocytic (NC5) cell line immortalized by EBV that expresses the type II latency program. Here we generated LMP1 dominant negative forms (DNs), based on fusion between green fluorescent protein (GFP) and transformation effector site 1 (TES1) or TES2 of LMP1. Then we generated cell lines conditionally expressing these DNs. These DNs inhibit NF-κB and Akt pathways, resulting in the impairment of survival processes and increased apoptosis in these cell lines. This proapoptotic effect is due to reduced interaction of LMP1 with specific adapters and the recruitment of these adapters to DNs, which enable the generation of an apoptotic complex involving TRADD, FADD, and caspase 8. Similar results were obtained with cell lines displaying a latency III program in which LMP1-DNs decrease cell viability. Finally, we prove that synthetic peptides display similar inhibitory effects in EBV-infected cells. DNs derived from LMP1 could be used to develop therapeutic approaches for malignant diseases associated with EBV.     

EBV latent membrane protein 1 activates Akt, NFkappaB, and Stat3 in B cell lymphomas

Latent membrane protein 1 (LMP1) is the major oncoprotein of Epstein-Barr virus (EBV). In transgenic mice, LMP1 promotes increased lymphoma development by 12 mo of age. This study reveals that lymphoma develops in B-1a lymphocytes, a population that is associated with transformation in older mice. The lymphoma cells have deregulated cell cycle markers, and inhibitors of Akt, NFkappaB, and Stat3 block the enhanced viability of LMP1 transgenic lymphocytes and lymphoma cells in vitro. Lymphoma cells are independent of IL4/Stat6 signaling for survival and proliferation, but have constitutively activated Stat3 signaling. These same targets are also deregulated in wild-type B-1a lymphomas that arise spontaneously through age predisposition. These results suggest that Akt, NFkappaB, and Stat3 pathways may serve as effective targets in the treatment of EBV-associated B cell lymphomas.     

The EBV transforming protein, latent membrane protein 1, mimics and cooperates with CD40 signaling in B lymphocytes

Latent membrane protein 1 (LMP1) is required for EBV-induced immortalization of human B cells, and expression of the protein in the absence of other viral proteins leads to an activated phenotype in B cells. It has been well documented that LMP1 causes B cells to up-regulate adhesion molecules, such as LFA-1 and ICAM-1, and coactivation molecules, such as B7-1 and CD23, as well as to activate NF-kappaB. Ligation of the endogenous B cell CD40 molecule also induces these and other activated phenotypic changes. Here, we report that expression of LMP1 also activates B cells to secrete Ig and IL-6 and rescues them from B cell receptor-mediated growth arrest analogous to CD40 signaling. Furthermore, an HLA-A2LMP1 chimeric construct demonstrates that the oligomerization of the carboxyl-terminal 200 amino acids of LMP1 is sufficient for B cell signaling. Finally, we demonstrate that LMP1 and CD40 signaling pathways interact cooperatively in inducing B cell effector functions.     

EBV latent membrane protein 2A induces autoreactive B cell activation and TLR hypersensitivity

EBV is associated with systemic lupus erythematosus (SLE), but how it might contribute to the etiology is not clear. Since EBV-encoded latent membrane protein 2A (LMP2A) interferes with normal B cell differentiation and function, we sought to determine its effect on B cell tolerance. Mice transgenic for both LMP2A and the Ig transgene 2-12H specific for the ribonucleoprotein Smith (Sm), a target of the immune system in SLE, develop a spontaneous anti-Sm response. LMP2A allows anti-Sm B cells to overcome the regulatory checkpoint at the early preplasma cell stage by a self-Ag-dependent mechanism. LMP2A induces a heightened sensitivity to TLR ligand stimulation, resulting in increased proliferation or Ab-secreting cell differentiation or both. Thus, we propose a model whereby LMP2A induces hypersensitivity to TLR stimulation, leading to activation of anti-Sm B cells through the BCR/TLR pathway. These data further implicate TLRs in the etiology of SLE and suggest a mechanistic link between EBV infection and SLE.