参考文献

Tryptophan (Trp) catabolism mediated by indoleamine 2,3-dioxygenase (IDO) plays a central role in the regulation of T-cell-mediated immune responses. In this study,we also demonstrate that natural killer (NK)-cell function can be influenced by IDO. Indeed,l-kynurenine,a Trp-derived catabolite resulting from IDO activity,was found to prevent the cytokine-mediated up-regulation of the expression and function of specific triggering receptors responsible for the induction of NK-cell-mediated killing. The effect of l-kynurenine appears to be restricted to NKp46 and NKG2D,while it does not affect other surface receptors such as NKp30 or CD16. As a consequence,l-kynurenine-treated NK cells display impaired ability to kill target cells recognized via NKp46 and NKG2D. Instead,they maintain the ability to kill targets,such as dendritic cells (DCs),that are mainly recognized via the NKp30 receptor. The effect of l-kynurenine,which is effective at both the transcriptional and the protein level,can be reverted,since NK cells were found to recover their functional competence after washing. View Publication

Human immunodeficiency virus type 1 (HIV-1) utilizes Vpu,Env,and Nef to down-modulate its primary CD4 receptor from the cell surface,and this function seems to be critical for the pathogenesis of AIDS. The physiological relevance of CD4 down-modulation,however,is currently not well understood. In the present study,we analyzed the kinetics of CD4 down-modulation and the susceptibility of HIV-1-infected T cells to superinfection using proviral HIV-1 constructs containing individual and combined defects in vpu,env,and nef and expressing red or green fluorescent proteins. T cells infected with HIV-1 mutants containing functional nef genes expressed low surface levels of CD4 from the first moment that viral gene expression became detectable. In comparison,Vpu and Env had only minor to moderate effects on CD4 during later stages of infection. Consistent with these quantitative differences,Nef inhibited superinfection more efficiently than Vpu and Env. Notably,nef alleles from AIDS patients were more effective in preventing superinfection than those derived from a nonprogressor of HIV-1 infection. Our data suggest that protection against X4-tropic HIV-1 superinfection involves both CD4-independent and CD4-dependent mechanisms of HIV-1 Nef. X4 was effectively down-regulated by simian immunodeficiency virus and HIV-2 but not by HIV-1 Nef proteins. Thus,maximal protection seems to involve an as-yet-unknown mechanism that is independent of CD4 or coreceptor down-modulation. Finally,we demonstrate that superinfected primary T cells show enhanced levels of apoptosis. Accordingly,one reason that HIV-1 inhibits CD4 surface expression and superinfection is to prevent premature cell death in order to expand the period of effective virus production. View Publication

Human metapneumovirus (hMPV) is a recently described member of the Paramyxoviridae family/Pneumovirinae subfamily and shares many common features with respiratory syncytial virus (RSV),another member of the same subfamily. hMPV causes respiratory tract illnesses that,similar to human RSV,occur predominantly during the winter months and have symptoms that range from mild to severe cough,bronchiolitis,and pneumonia. Like RSV,the hMPV virus can be subdivided into two genetic subgroups,A and B. With RSV,a single monoclonal antibody directed at the fusion (F) protein can prevent severe lower respiratory tract RSV infection. Because of the high level of sequence conservation of the F protein across all the hMPV subgroups,this protein is likely to be the preferred antigenic target for the generation of cross-subgroup neutralizing antibodies. Here we describe the generation of a panel of neutralizing monoclonal antibodies that bind to the hMPV F protein. A subset of these antibodies has the ability to neutralize prototypic strains of both the A and B hMPV subgroups in vitro. Two of these antibodies exhibited high-affinity binding to the F protein and were shown to protect hamsters against infection with hMPV. The data suggest that a monoclonal antibody could be used prophylactically to prevent lower respiratory tract disease caused by hMPV. View Publication

Regulatory T (T reg) cells are critical regulators of immune tolerance. Most T reg cells are defined based on expression of CD4,CD25,and the transcription factor,FoxP3. However,these markers have proven problematic for uniquely defining this specialized T cell subset in humans. We found that the IL-7 receptor (CD127) is down-regulated on a subset of CD4(+) T cells in peripheral blood. We demonstrate that the majority of these cells are FoxP3(+),including those that express low levels or no CD25. A combination of CD4,CD25,and CD127 resulted in a highly purified population of T reg cells accounting for significantly more cells that previously identified based on other cell surface markers. These cells were highly suppressive in functional suppressor assays. In fact,cells separated based solely on CD4 and CD127 expression were anergic and,although representing at least three times the number of cells (including both CD25(+)CD4(+) and CD25(-)CD4(+) T cell subsets),were as suppressive as the classic" CD4(+)CD25(hi) T reg cell subset. Finally� View Publication

Activation of natural killer (NK) cell cytotoxicity requires adhesion and formation of a conjugate with a susceptible target cell,followed by actin polymerization,and polarization of the microtubule organizing center (MTOC) and cytolytic granules to the NK cell immune synapse. Here,by using the YTS NK cell line as a model,CD28 is shown to be an activating receptor. It signals cytotoxicity in a process dependent on phosphoinositide-3 kinase activation,leading to sustained extracellular signal-regulated kinase 2 (ERK2) phosphorylation. ERK and phospho-ERK localize to microtubule filaments. Neither conjugation with targets nor actin polymerization is affected by blocking ERK2 activation. However,both polarization of the MTOC and cytolytic granules to the synaptic region and NK cell cytotoxicity are strongly reduced by blocking ERK2 activation. A role for the CD28/CD80 interaction in cytotoxicity of human peripheral NK cells also was established. By contrast,lymphocyte function-associated antigen 1 (LFA-1) ligation transduces only a transient ERK2 activation and fails to induce killing in YTS cells. Thus,in YTS cells,a CD28 signal is used to polarize the MTOC and cytolytic granules to the NK cell immune synapse by stimulating sustained ERK2 activation. View Publication

Respiratory failure during Pneumocystis pneumonia is mainly a consequence of exaggerated inflammatory responses to the organism. Dendritic cells (DCs) are the most potent APCs in the lung and are key to the regulation of innate and adaptive immune responses. However,their participation in the inflammatory response directed against Pneumocystis infection has not been fully elucidated. Therefore,we studied the role of Pneumocystis carinii,as well as Saccharomyces cerevisiae,cell wall-derived beta-glucans,in DC costimulatory molecule expression. We further studied the impact of beta-glucans on subsequent T cell activation. Because cytokine secretion by DCs has recently been shown to be regulated by Fas ligand (FasL),its role in beta-glucan activation of DCs was also investigated. beta-Glucan-induced DC activation occurred in part through dectin-1 receptors. We demonstrated that DC activation by beta-glucans elicits T cell activation and polarization into a Th1 patterned response,but with the conspicuous absence of IL-12. These observations differed from LPS-driven T cell polarization,suggesting that beta-glucans and LPS signal DC activation through different mechanisms. We additionally determined that IL-1beta and TNF-alpha secretion by beta-glucan-stimulated DCs was partially regulated by Fas-FasL. This suggests that dysregulation of FasL could further enhance exuberant and prolonged cytokine production by DCs following DC-T cell interactions,further promoting lung inflammation typical of Pneumocystis pneumonia. View Publication

Human complement receptor type 2 (CR2/CD21) is a B lymphocyte membrane glycoprotein that plays a central role in the immune responses to foreign Ags as well as the development of autoimmunity to nuclear Ags in systemic lupus erythematosus. In addition to these three well-characterized ligands,C3d/iC3b,EBV-gp350,and CD23,a previous study has identified CR2 as a potential receptor for IFN-alpha. IFN-alpha,a multifunctional cytokine important in the innate immune system,has recently been proposed to play a major pathogenic role in the development of systemic lupus erythematosus in humans and mice. In this study,we have shown using surface plasmon resonance and ELISA approaches that CR2 will bind IFN-alpha in the same affinity range as the other three well-characterized ligands studied in parallel. In addition,we show that IFN-alpha interacts with short consensus repeat domains 1 and 2 in a region that serves as the ligand binding site for C3d/iC3b,EBV-gp350,and CD23. Finally,we show that treatment of purified human peripheral blood B cells with the inhibitory anti-CR2 mAb 171 diminishes the induction of IFN-alpha-responsive genes. Thus,IFN-alpha represents a fourth class of extracellular ligands for CR2 and interacts with the same domain as the other three ligands. Defining the role of CR2 as compared with the well-characterized type 1 IFN-alpha receptor 1 and 2 in mediating innate immune and autoimmune roles of this cytokine should provide additional insights into the biologic roles of this interaction. View Publication

Langerhans cells (LC) are a unique subset of dendritic cells (DC),present in the epidermis and serving as the first line of defense against pathogens invading the skin. To investigate the role of human LCs in innate immune responses,we examined TLR expression and function of LC-like DCs derived from CD34+ progenitor cells and compared them to DCs derived from peripheral blood monocytes (monocyte-derived DC; Mo-DC). LC-like DCs and Mo-DCs expressed TLR1-10 mRNAs at comparable levels. Although many of the TLR-induced cytokine patterns were similar between the two cell types,stimulation with the TLR3 agonist poly(I:C) triggered significantly higher amounts of the IFN-inducible chemokines CXCL9 (monokine induced by IFN-gamma) and CXCL11 (IFN-gamma-inducible T cell alpha chemoattractant) in LC-like DCs as compared with Mo-DCs. Supernatants from TLR3-activated LC-like DCs reduced intracellular replication of vesicular stomatitis virus in a type I IFN-dependent manner. Finally,CXCL9 colocalized with LCs in skin biopsy specimens from viral infections. Together,our data suggest that LCs exhibit a direct antiviral activity that is dependent on type I IFN as part of the innate immune system. View Publication

Dendritic cells (DCs) are potent mediators of the immune response,and can be activated by exogenous pathogen components. Galectin-1 is a member of the conserved beta-galactoside-binding lectin family that binds galactoside residues on cell surface glycoconjugates. Galectin-1 is known to play a role in immune regulation via action on multiple immune cells. However,its effects on human DCs are unknown. In this study,we show that galectin-1 induces a phenotypic and functional maturation in human monocyte-derived DCs (MDDCs) similar to but distinct from the activity of the exogenous pathogen stimuli,LPS. Immature human MDDCs exposed to galectin-1 up-regulated cell surface markers characteristic of DC maturation (CD40,CD83,CD86,and HLA-DR),secreted high levels of IL-6 and TNF-alpha,stimulated T cell proliferation,and showed reduced endocytic capacity,similar to LPS-matured MDDCs. However,unlike LPS-matured DCs,galectin-1-treated MDDCs did not produce the Th1-polarizing cytokine IL-12. Microarray analysis revealed that in addition to modulating many of the same DC maturation genes as LPS,galectin-1 also uniquely up-regulated a significant subset of genes related to cell migration through the extracellular matrix (ECM). Indeed,compared with LPS,galectin-1-treated human MDDCs exhibited significantly better chemotactic migration through Matrigel,an in vitro ECM model. Our findings show that galectin-1 is a novel endogenous activator of human MDDCs that up-regulates a significant subset of genes distinct from those regulated by a model exogenous stimulus (LPS). One unique effect of galectin-1 is to increase DC migration through the ECM,suggesting that galectin-1 may be an important component in initiating an immune response. View Publication

NK cells express an activating FcR (FcgammaRIIIa) that mediates Ab-dependent cellular cytotoxicity and the production of immune modulatory cytokines in response to Ab-coated targets. IL-21 has antitumor activity in murine models that depends in part on its ability to promote NK cell cytotoxicity and IFN-gamma secretion. We hypothesized that the NK cell response to FcR stimulation would be enhanced by the administration of IL-21. Human NK cells cultured with IL-21 and immobilized IgG or human breast cancer cells coated with a therapeutic mAb (trastuzumab) secreted large amounts of IFN-gamma. Increased secretion of TNF-alpha and the chemokines IL-8,MIP-1alpha,and RANTES was also observed under these conditions. NK cell IFN-gamma production was dependent on distinct signals mediated by the IL-21R and the FcR and was abrogated in STAT1-deficient NK cells. Supernatants derived from NK cells that had been stimulated with IL-21 and mAb-coated breast cancer cells were able to drive the migration of naive and activated T cells in an in vitro chemotaxis assay. IL-21 also enhanced NK cell lytic activity against Ab-coated tumor cells. Coadministration of IL-21 and Ab-coated tumor cells to immunocompetent mice led to synergistic production of IFN-gamma by NK cells. Furthermore,the administration of IL-21 augmented the effects of an anti-HER2/neu mAb in a murine tumor model,an effect that required IFN-gamma. These findings demonstrate that IL-21 significantly enhances the NK cell response to Ab-coated targets and suggest that IL-21 would be an effective adjuvant to administer in combination with therapeutic mAbs. View Publication