Host and viral factors in the immunopathogenesis of primary hepatitis C virus infection

Individuals infected with hepatitis C virus (HCV) have two possible outcomes of infection, clearance or persistent infection. The focus of this review is the host mechanisms that facilitate clearance. The interaction between HCV viral components and the immune system ultimately determines the balance between the virus and host. Strong evidence points to the aspects of cellular immune response as the key determinants of outcome. The recent discovery of viral evasion strategies targeting innate immunity suggests that the interferon-alpha/beta induction pathways are also critical. A growing body of evidence has implicated polymorphisms in both innate and adaptive immune response genes as determinants of viral clearance in individuals infected with HCV.     

Salmonella enterica Serovar Typhi Plasmid Impairs Dendritic Cell Responses to Infection

Salmonella enterica serovar Typhi (S. typhi) evades from innate immunity by expression of a variety of pathogenic factors. The "pR(ST98)" plasmid of S. typhi is involved in multidrug-resistant and virulence of S. typhi. However, its exact effect on host cell function remains elusive. Dendritic cells (DCs) play an important role in shaping immune response against Salmonella. For the purpose of investigation whether pR(ST98) might target DCs involved in adaptive immune response, murine DCs were infected with S. typhi wild type and mutant strains. S. typhi stimulation resulted in up-regulation of costimulatory molecules on DCs. S. typhi wild type resulted in decreased up-regulation of CD40, CD80, and CD86 expression. Experiments with S. typhi pR(ST98) mutant (S. typhi-Δ-pR(ST98)) and S. typhi-Δ-pR(ST98) with a complemented plasmid encoding pR(ST98) (S. typhi-c-pR(ST98)) revealed that pR(ST98) accounts for inhibition of surface molecule expression and functional maturity. S. typhi-Δ-pR(ST98) gave maximal levels of IL-12 and IFN-γ release compared with wild type S. typhi or the complemented strains. In contrast to IL-12 and IFN-γ, IL-10 secretion by S. typhi-Δ-pR(ST98)-infected DCs was significantly lower than induction by S. typhi wild type. This indicates that immunity in response to pR(ST98) is skewed away from a protective Th1 response. Moreover, infection with S. typhi-Δ-pR(ST98) induced autophagy in DCs. We herein demonstrate S. typhi pR(ST98) plays essential roles in modulating DCs maturation, activation, inflammatory responses, and autophagy. Together, these data prove that pR(ST98) targets functions of DCs that are required for T-cell activation. This might contribute to evasion of adaptive immune responses by S. typhi.     

Human metapneumovirus glycoprotein G inhibits TLR4-dependent signaling in monocyte-derived dendritic cells

Human metapneumovirus (hMPV) is a major cause of upper and lower respiratory infections in children and adults. Recent work from our group demonstrated that hMPV G glycoprotein is an important virulence factor, responsible for inhibiting innate immune responses in airway epithelial cells. Myeloid dendritic cells (DCs) are potent APCs and play a major role in initiating and modulating the innate and adaptive immune responses. In this study, we found that TLR4 plays a major role in hMPV-induced activation of monocyte-derived DCs (moDCs), as downregulation of its expression by small interfering RNA significantly blocked hMPV-induced chemokine and type I IFN expression. Similar results were found in bone marrow-derived DCs from TLR4-deficient mice. moDCs infected with a virus lacking G protein expression produced higher levels of cytokines and chemokines compared with cells infected with wild-type virus, suggesting that G protein plays an inhibitory role in viral-induced cellular responses. Specifically, G protein affects TLR4-dependent signaling, as infection of moDCs with recombinant hMPV lacking G protein inhibited LPS-induced production of cytokine and chemokines significantly less than did wild-type virus, and treatment of moDCs with purified G protein resulted in a similar inhibition of LPS-dependent signaling. Our results demonstrate that hMPV G protein plays an important role in inhibiting host innate immune responses, likely affecting adaptive responses too.     

Cytokines as critical co-stimulatory molecules in modulating the immune response of natural killer cells

Cytokines are involved in directing the activation of natural killer （NK） cells. NK cells are involved in the recognition of cells that have been altered; thus they do not recognize specific insults to the host, but when activated, are capable of destroying infected cells directly, as well as promoting the recruitment and response of the other components of the immune system by the release of cytokines and chemokines. It is these properties that have made NK cells a critical part of innate immunity and adaptive immunity, and they play a principal role linking innate and adaptive immunity by the recruitment of an adaptive immune response to an innate immune reaction.     

Alternate Reading Frame Protein (F Protein) of Hepatitis C Virus: Paradoxical Effects of Activation and Apoptosis on Human Dendritic Cells Lead to Stimulation of T Cells

Hepatitis C virus (HCV) leads to chronic infection in the majority of infected individuals due to lack, failure, or inefficiency of generated adaptive immune responses. In a minority of patients, acute infection is followed by viral clearance. The immune correlates of viral clearance are not clear yet but have been extensively investigated, suggesting that multispecific and multifunctional cellular immunity is involved. The generation of cellular immunity is highly dependent upon how antigen presenting cells (APCs) process and present various viral antigens. Various structural and non-structural HCV proteins derived from the open reading frame (ORF) have been implicated in modulation of dendritic cells (DCs) and APCs. Besides the major ORF proteins, the HCV core region also encodes an alternate reading frame protein (ARFP or F), whose function in viral pathogenesis is not clear. In the current studies, we sought to determine the role of HCV-derived ARFP in modulating dendritic cells and stimulation of T cell responses. Recombinant adenovirus vectors containing F or core protein derived from HCV (genotype 1a) were prepared and used to endogenously express these proteins in dendritic cells. We made an intriguing observation that endogenous expression of F protein in human DCs leads to contrasting effects on activation and apoptosis of DCs, allowing activated DCs to efficiently internalize apoptotic DCs. These in turn result in efficient ability of DCs to process and present antigen and to prime and stimulate F protein derived peptide-specific T cells from HCV-naive individuals. Taken together, our findings suggest important aspects of F protein in modulating DC function and stimulating T cell responses in humans.     

Toll样受体与树突状细胞介导的天然免疫和获得性免疫

树突状细胞(dendritic cells,DCs)作为迄今所发现的抗原提呈功能最强的一类抗原提呈细胞,是联结天然免疫和获得性免疫的桥梁。Toll样受体(Toll-like receptors,TLRs)是一类进化保守的胚系编码的模式识别受体,在DCs的抗原识别、递呈及激活T细胞等方面具有重要作用,是机体受外来抗原入侵后作出适当免疫反应的调控点。现就TLRs在不同DCs亚群中的分布、与DCs介导的天然免疫和获得性免疫的关系及DCs功能可塑性的分子基础作一综述。     

Surfactant protein A modulates the differentiation of murine bone marrow-derived dendritic cells

Surfactant protein A (SP-A) is an innate immune molecule that regulates pathogen clearance and lung inflammation. SP-A modulates innate immune functions such as phagocytosis, cytokine production, and chemotaxis; however, little is known about regulation of adaptive immunity by SP-A. Dendritic cells (DCs) are the most potent antigen-presenting cell with the unique capacity to activate naive T cells and initiate adaptive immunity. The goal of this study was to test the hypothesis that SP-A regulates the differentiation of immature DCs into potent T cell stimulators. The data show that incubation of immature DCs for 24 h with SP-A inhibits basal- and LPS-mediated expression of major histocompatibility complex class II and CD86. Stimulation of immature DCs by SP-A also inhibits the allostimulation of T cells, enhances dextran endocytosis, and alters DC chemotaxis toward RANTES and secondary lymphoid tissue chemokine. The effects on DC phenotype and function are similar for the structurally homologous C1q, but not for SP-D. These studies demonstrate that SP-A participates in the adaptive immune response by modulating important immune functions of DCs.     

Immature human dendritic cells infected with Leishmania infantum are resistant to NK-mediated cytolysis but are efficiently recognized by NKT cells

Dendritic cells (DC) play an important role in innate and adaptive immunity, interacting with T cells, NK, and NKT cells. A critical step in the interaction of the parasitic protozoa Leishmania with their host is the evasion of both innate and adaptive immunity, producing a long-lasting chronic infection. There is growing evidence that these parasites can modify the Ag-presenting and immunoregulatory functions of DCs. The cells and mechanisms involved in innate immune response against Leishmania are still poorly understood. In this study, we investigated how Leishmania infantum infection affects DC interactions with NK and invariant NKT (iNKTs) cells in humans. We found that infected immature DCs (iDCs) do not up-regulate HLA class I molecules. Despite this, iDCs become resistant to killing mediated by autologous NK cells due to the up-regulation of HLA-E expression, which protects target cells from NK-mediated lysis through interaction with the inhibitory receptor CD94/NKG2A. Furthermore, iDCs infected with L. infantum up-regulate CD1d cell surface expression and consequently can be efficiently recognized and killed by iNKT cells that produce IFN-gamma. These data suggest that L. infantum could be able to evade NK recognition; in contrast, iNKTs may play an important role in the immune response against Leishmania.     

Hepatitis C virus (HCV) employs multiple strategies to subvert the host innate antiviral response

Hepatitis C virus (HCV) is a serious global health problem which accounts for approximately 40% of chronic liver diseases worldwide. HCV frequently establishes a persistent infection, although it is recognized and targeted by innate immunity as well as cellular and humoral immune mechanisms. This suggests that HCV has developed powerful strategies to escape elimination by innate and adaptive immunity. HCV-induced liver injury is thought to be mainly immune-mediated rather than due to direct cytopathic effects of the virus. Hence, therapeutic strategies should target those mechanisms favoring viral persistence since unspecific enhancement of host antiviral immunity may theoretically also promote liver injury. The present review summarizes our current understanding of how the hepatitis C virus interferes with the innate antiviral host-response to establish persistent infection.     

Functional inactivation of immature dendritic cells by the intracellular parasite Toxoplasma gondii

Despite its noted ability to induce strong cellular immunity, and its known susceptibility to IFN-gamma-dependent immune effector mechanisms, the protozoan Toxoplasma gondii is a highly successful parasite, able to replicate, disseminate, and either kill the host or, more commonly, establish resistant encysted life forms before the emergence of protective immune responses. We sought to understand how the parasite gains the advantage. Using transgenic clonal parasite lines engineered to express fluorescent markers in combination with dendritic cells (DC) grown from the bone marrow of wild-type mice or transgenic mice expressing fluorescent protein-tagged MHC class II molecules, we used flow cytometry and fluorescence microscopy to analyze the responses of infected DC to both invasion by the parasite and subsequent DC maturation signals. We found that T. gondii preferentially invades immature dendritic cells but fails to activate them in the process, and renders them resistant to subsequent activation by TLR ligands or the immune-system-intrinsic maturation signal CD40L. The functional consequences of T. gondii-mediated suppression of DC activation are manifested in a relative inability of infected immature DC to activate naive CD4(+) Th lymphocytes, or to secrete cytokines, such IL-12 and TNF-alpha, that play important roles in innate and/or adaptive immunity. The findings reveal that T. gondii suppresses the ability of immature DC to participate in innate immunity and to induce adaptive immune responses. The ability of T. gondii to temporarily evade recognition could provide a selective advantage that permits dissemination and establishment before adaptive immune response initiation.     

Who is in control of the stickleback immune system: interactions between Schistocephalus solidus and its specific vertebrate host

The cestode Schistocephalus solidus is a frequent parasite of three-spined sticklebacks and has a large impact on its host's fitness. Selection pressure should therefore be high on stickleback defence mechanisms, like an efficient immune system, and also on parasite strategies to overcome these. Even though there are indications for manipulation of the immune system of its specific second intermediate host by the cestode, nothing is yet known about the chronology of specific interactions of S. solidus with the stickleback immune system. We here expected sticklebacks to first mount an innate immune response directly post-exposure to the parasite to clear the infection at an early stage and after an initial lag phase to upregulate adaptive immunity. Most interestingly, we did not find any upregulation of the specific lymphocyte-mediated immune response. Also, the pattern of activation of the innate immune system did not match our expectations: the proliferation of monocytes followed fluctuating kinetics suggesting that the parasite repeatedly installs a new surface coat not immunogenic to the host. Furthermore, the respiratory burst activity, which has the potential to clear an early S. solidus infection, was upregulated very late during infection, when the parasite was too big to be cleared but ready for transmission to its final host. We here suggest that the late activation of the innate immune system interferes with the neuroendocrine system, which mediates reduced predation avoidance behaviour and so facilitates the transmission to the final host.     

Hepatitis C virus nonstructural protein 5A modulates the toll-like receptor-MyD88-dependent signaling pathway in macrophage cell lines

Hepatitis C virus (HCV) infection induces a wide range of chronic liver injuries; however, the mechanism through which HCV evades the immune surveillance system remains obscure. Blood dendritic cells (DCs) play a pivotal role in the recognition of viral infection and the induction of innate and adaptive immune responses. Several reports suggest that HCV infection induces the dysfunction of DCs in patients with chronic hepatitis C. Toll-like receptor (TLR) has been shown to play various roles in many viral infections; however, the involvement of HCV proteins in the TLR signaling pathway has not yet been precisely elucidated. In this study, we established mouse macrophage cell lines stably expressing HCV proteins and determined the effect of HCV proteins on the TLR signaling pathways. Immune cells expressing NS3, NS3/4A, NS4B, or NS5A were found to inhibit the activation of the TLR2, TLR4, TLR7, and TLR9 signaling pathways. Various genotypes of NS5A bound to MyD88, a major adaptor molecule in TLR, inhibited the recruitment of interleukin-1 receptor-associated kinase 1 to MyD88, and impaired cytokine production in response to TLR ligands. Amino acid residues 240 to 280, previously identified as the interferon sensitivity-determining region (ISDR) in NS5A, interacted with the death domain of MyD88, and the expression of a mutant NS5A lacking the ISDR partially restored cytokine production. These results suggest that the expression of HCV proteins modulates the TLR signaling pathway in immune cells.     

禽坦布苏病毒诱导的宿主免疫应答

禽坦布苏病毒(Avian Tembusu virus,ATMUV)是近年来在我国新发现的一种病毒,可感染多种蛋禽,感染动物临床特征为采食量下降,产蛋量骤减,甚至停产,感染后期呈神经症状,如腿和翅膀麻痹、共济失调等。ATMUV在我国多个省市地区流行,给我国甚至世界养禽业带来严重影响。固有免疫是机体抵抗病原感染的第一道重要防线,是机体与生俱来的抵御病原微生物的能力。适应性免疫是机体免疫系统在抗原刺激下产生特异性抗体及免疫效应细胞的过程,以建立针对某种病原微生物的抵抗力,是机体免疫系统的重要部分。本文将从禽坦布苏病毒诱导宿主固有免疫应答和适应性免疫应答两方面进行综述。     

DNA damage: a trigger of innate immunity but a requirement for adaptive immune homeostasis

Chromosome breakage is frequently associated with viral infection and cellular transformation, but it is also required for two processes that are crucial for the development and function of adaptive immunity: V(D)J recombination and class-switch recombination. The cellular responses that result from this type of DNA damage, which are mostly activated by the protein kinase ataxia-telangiectasia mutated (ATM), lead to cell-cycle arrest at several checkpoints and efficient DNA repair. This Review focuses on the important roles of these DNA-damage responses in the activation of innate immunity and the targeting of the innate immune response to infected or transformed cells, as well as in the development and function of adaptive immunity.     

禽沙门菌诱导宿主免疫应答的特性

沙门菌病(Salmonellosis)是全世界最普遍的食源性疾病之一,不仅对养殖业造成经济损失,还对人类安全构成威胁。禽沙门菌感染肠道后,可诱导肠上皮细胞表达多种TLRs和炎症反应的发生,在分泌的趋化因子作用下免疫效应细胞迁移到感染部位。细菌通过肠上皮细胞屏障后被巨噬细胞或树突状细胞吞噬,其中巨噬细胞是沙门菌的主要定殖场所。天然免疫系统将抗原递呈给淋巴细胞后,机体能够在2–3周内通过以Th1为主的免疫应答清除在肠道和深层组织中的沙门菌。而宿主特异性血清型鸡白痢沙门菌从肠道侵入后,在肝脾和其他器官中定殖,进而引发全身感染。早期感染阶段不会引起肠道炎症反应,主要诱导以Th2为主的免疫应答,而Th1型应答相对较弱,有利于鸡白痢沙门菌在机体内的持续存在和感染。本文围绕禽沙门菌的致病机理和免疫应答特性进行阐述,尤其对鸡白痢沙门菌免疫逃逸和持续载菌的特性进行深入分析,为禽沙门菌病的防控提供新靶标和新见解。     

IPS-1 Is Essential for the Control of West Nile Virus Infection and Immunity

The innate immune response is essential for controlling West Nile virus (WNV) infection but how this response is propagated and regulates adaptive immunity in vivo are not defined. Herein, we show that IPS-1, the central adaptor protein to RIG-I-like receptor (RLR) signaling, is essential for triggering of innate immunity and for effective development and regulation of adaptive immunity against pathogenic WNV. IPS-1^−/− mice exhibited increased susceptibility to WNV infection marked by enhanced viral replication and dissemination with early viral entry into the CNS. Infection of cultured bone-marrow (BM) derived dendritic cells (DCs), macrophages (Macs), and primary cortical neurons showed that the IPS-1-dependent RLR signaling was essential for triggering IFN defenses and controlling virus replication in these key target cells of infection. Intriguingly, infected IPS-1^−/− mice displayed uncontrolled inflammation that included elevated systemic type I IFN, proinflammatory cytokine and chemokine responses, increased numbers of inflammatory DCs, enhanced humoral responses marked by complete loss of virus neutralization activity, and increased numbers of virus-specific CD8+ T cells and non-specific immune cell proliferation in the periphery and in the CNS. This uncontrolled inflammatory response was associated with a lack of regulatory T cell expansion that normally occurs during acute WNV infection. Thus, the enhanced inflammatory response in the absence of IPS-1 was coupled with a failure to protect against WNV infection. Our data define an innate/adaptive immune interface mediated through IPS-1-dependent RLR signaling that regulates the quantity, quality, and balance of the immune response to WNV infection.     

Hepatitis C virus present in the sera of infected patients interferes with the autophagic process of monocytes impairing their in-vitro differentiation into dendritic cells

Autophagy has a pivotal role in the in-vitro monocyte differentiation into macrophages and dendritic cells (DCs), the most powerful antigen presenting cells (APC) with the unique capacity to initiate an adaptive immune response. Autophagy is also a mechanism by which these cells of innate immunity may degrade intracellular pathogens and mediate the antigen processing and presentation, essential to clear an infection. For these reasons, pathogens have learned how to manipulate autophagy for their own survival. In this study we found that hepatitis C virus (HCV), derived from sera of infected patients, blocked the autophagic process in differentiating monocytes, seen as LC3 II and p62 expression levels. The suppression of autophagy correlated with a reduction of cathepsins D, B and proteolytic activity, and resulted in impairment of monocyte differentiation into DCs, as indicated by the reduction of CD1a acquirement. These data suggest that the block of autophagy might be one of the underlying mechanisms of the HCV-mediated immune subversion that frequently leads to viral persistence and chronic hepatitis.     

CD40 ligand-dependent activation of cytotoxic T lymphocytes by adeno-associated virus vectors in vivo: role of immature dendritic cells

Recombinant adeno-associated virus type 2 (rAAV) is being explored as a vector for gene therapy because of its broad host range, good safety profile, and persistent transgene expression in vivo. However, accumulating evidence indicates that administration of AAV vector may initiate a detectable cellular and humoral immune response to its transduced neo-antigen in vivo. To elucidate the cellular basis of the AAV-mediated immune response, C57BL/6 mouse bone marrow-derived immature and mature dendritic cells (DCs) were infected with AAV encoding beta-galactosidase (AAV-lacZ) and adoptively transferred into mice that had received an intramuscular injection of AAV-lacZ 10 days earlier. Unexpectedly, C57BL/6 mice but not CD40 ligand-deficient (CD40L(-/-)) mice adoptively transferred with AAV-lacZ-infected immature DCs developed a beta-galactosidase-specific cytotoxic T-lymphocyte (CTL) response that markedly diminished AAV-lacZ-transduced gene expression in muscle fibers. In contrast, adoptive transfer of AAV-lacZ-infected mature DCs failed to elicit a similar CTL response in vivo. Our findings indicate, for the first time, that immature DCs may be able to elicit a CD40L-dependent T-cell immunity to markedly diminish AAV-lacZ transduced gene expression in vivo when a sufficient number of DCs capturing rAAV vector and/or its transduced gene products is recruited.     

MDA-5 recognition of a murine norovirus

Noroviruses are important human pathogens responsible for most cases of viral epidemic gastroenteritis worldwide. Murine norovirus-1 (MNV-1) is one of several murine noroviruses isolated from research mouse facilities and has been used as a model of human norovirus infection. MNV-1 infection has been shown to require components of innate and adaptive immunity for clearance; however, the initial host protein that recognizes MNV-1 infection is unknown. Because noroviruses are RNA viruses, we investigated whether MDA5 and TLR3, cellular sensors that recognize dsRNA, are important for the host response to MNV-1. We demonstrate that MDA5-/- dendritic cells(DC) have a defect in cytokine response to MNV-1. In addition, MNV-1 replicates to higher levels in MDA5-/- DCs as well as in MDA5-/- mice in vivo. Interestingly, TLR3-/- DCs do not have a defect in vitro, but TLR3-/- mice have a slight increase in viral titers. This is the first demonstration of an innate immune sensor for norovirus and shows that MDA5 is required for the control of MNV-1 infection. Knowledge of the host response to MNV-1 may provide keys for prevention and treatment of the human disease.