SIV infection of natural host species such as sooty mangabeys results in high viral replication without clinical signs of simian AIDS. Studying such infections is useful for identifying immunologic parameters that lead to AIDS in HIV-infected patients. Here we have demonstrated that acute, SIV-induced CD4+ T cell depletion in sooty mangabeys does not result in immune dysfunction and progression to simian AIDS and that a population of CD3+CD4–CD8– T cells (double-negative T cells) partially compensates for CD4+ T cell function in these animals. Passaging plasma from an SIV-infected sooty mangabey with very few CD4+ T cells to SIV-negative animals resulted in rapid loss of CD4+ T cells. Nonetheless, all sooty mangabeys generated SIV-specific antibody and T cell responses and maintained normal levels of plasma lipopolysaccharide. Moreover, all CD4-low sooty mangabeys elicited a de novo immune response following influenza vaccination. Such preserved immune responses as well as the low levels of immune activation observed in these animals were associated with the presence of double-negative T cells capable of producing Th1, Th2, and Th17 cytokines. These studies indicate that SIV-infected sooty mangabeys do not appear to rely entirely on CD4+ T cells to maintain immunity and identify double-negative T cells as a potential subset of cells capable of performing CD4+ T cell–like helper functions upon SIV-induced CD4+ T cell depletion in this species.
Jeffrey M. Milush, Kiran D. Mir, Vasudha Sundaravaradan, Shari N. Gordon, Jessica Engram, Christopher A. Cano, Jacqueline D. Reeves, Elizabeth Anton, Eduardo O’Neill, Eboneé Butler, Kathy Hancock, Kelly S. Cole, Jason M. Brenchley, James G. Else, Guido Silvestri, Donald L. Sodora
Both mucosal and systemic immune responses are required for preventing or containing HIV transmission and chronic infection. However, currently described vaccination approaches are largely ineffective in inducing both mucosal and systemic responses. In this study, we found that the ubiquitin-editing enzyme A20 — an inducible feedback inhibitor of the TNFR, RIG-I, and TLR signaling pathways that broadly controls the maturation, cytokine production, and immunostimulatory potency of DCs — restricted systemically immunized DCs to induce both robust mucosal and systemic HIV-specific cellular and humoral responses. Mechanistic studies revealed that A20 regulated DC production of retinoic acid and proinflammatory cytokines, inhibiting the expression of gut-homing receptors on T and B cells. Furthermore, A20-silenced, hyperactivated DCs exhibited an enhanced homing capacity to draining and gut-associated lymphoid tissues (GALTs) after systemic administration. Thus, this study provides insights into the role of A20 in innate immunity. This work may allow the development of an efficient HIV vaccination strategy that is capable of inducing both robust systemic and mucosal anti-HIV cellular and humoral responses.
Bangxing Hong, Xiao-Tong Song, Lisa Rollins, Lindsey Berry, Xue F. Huang, Si-Yi Chen
Autophagy, a process for catabolizing cytoplasmic components, has been implicated in the modulation of interactions between RNA viruses and their host. However, the mechanism underlying the functional role of autophagy in the viral life cycle still remains unclear. Hepatitis C virus (HCV) is a single-stranded, positive-sense, membrane-enveloped RNA virus that can cause chronic liver disease. Here we report that HCV induces the unfolded protein response (UPR), which in turn activates the autophagic pathway to promote HCV RNA replication in human hepatoma cells. Further analysis revealed that the entire autophagic process through to complete autolysosome maturation was required to promote HCV RNA replication and that it did so by suppressing innate antiviral immunity. Gene silencing or activation of the UPR-autophagy pathway activated or repressed, respectively, IFN-β activation mediated by an HCV-derived pathogen-associated molecular pattern (PAMP). Similar results were achieved with a PAMP derived from Dengue virus (DEV), indicating that HCV and DEV may both exploit the UPR-autophagy pathway to escape the innate immune response. Taken together, these results not only define the physiological significance of HCV-induced autophagy, but also shed light on the knowledge of host cellular responses upon HCV infection as well as on exploration of therapeutic targets for controlling HCV infection.
Po-Yuan Ke, Steve S.-L. Chen
Having successfully developed mechanisms to evade immune clearance, hepatitis C virus (HCV) establishes persistent infection in approximately 75%–80% of patients. In these individuals, the function of HCV-specific CD8+ T cells is impaired by ligation of inhibitory receptors, the repertoire of which has expanded considerably in the past few years. We hypothesized that the coexpression of the negative regulatory receptors T cell immunoglobulin and mucin domain–containing molecule 3 (Tim-3) and programmed death 1 (PD-1) in HCV infection would identify patients at risk of developing viral persistence during and after acute HCV infection. The frequency of PD-1–Tim-3– HCV-specific CTLs greatly outnumbered PD-1+Tim-3+ CTLs in patients with acute resolving infection. Moreover, the population of PD-1+Tim-3+ T cells was enriched for within the central memory T cell subset and within the liver. Blockade of either PD-1 or Tim-3 enhanced in vitro proliferation of HCV-specific CTLs to a similar extent, whereas cytotoxicity against a hepatocyte cell line that expressed cognate HCV epitopes was increased exclusively by Tim-3 blockade. These results indicate that the coexpression of these inhibitory molecules tracks with defective T cell responses and that anatomical differences might account for lack of immune control of persistent pathogens, which suggests their manipulation may represent a rational target for novel immunotherapeutic approaches.
Rachel H. McMahan, Lucy Golden-Mason, Michael I. Nishimura, Brian J. McMahon, Michael Kemper, Todd M. Allen, David R. Gretch, Hugo R. Rosen
CD8+ T cells play a critical role in the immune response to viral pathogens. Persistent human cytomegalovirus (HCMV) infection results in a strong increase in the number of virus-specific, quiescent effector-type CD8+ T cells with constitutive cytolytic activity, but the molecular pathways involved in the induction and maintenance of these cells are unknown. We show here that HCMV infection induced acute and lasting changes in the transcriptomes of virus-reactive T cells collected from HCMV-seropositive patients at distinct stages of infection. Enhanced cell cycle and metabolic activity was restricted to the acute phase of the response, but at all stages, HCMV-specific CD8+ T cells expressed the Th1-associated transcription factors T-bet (TBX21) and eomesodermin (EOMES), in parallel with continuous expression of IFNG mRNA and IFN-γ–regulated genes. The cytolytic proteins granzyme B and perforin as well as the fractalkine-binding chemokine receptor CX3CR1 were found in virus-reactive cells throughout the response. During HCMV latency, virus-specific CD8+ T cells lacked the typical features of exhausted cells found in other chronic infections. Persistent effector cell traits together with the permanent changes in chemokine receptor usage of virus-specific, nonexhausted, long-lived CD8+ T cells may be crucial to maintain lifelong protection from HCMV reactivation.
Kirsten M.L. Hertoghs, Perry D. Moerland, Amber van Stijn, Ester B.M. Remmerswaal, Sila L. Yong, Pablo J.E.J. van de Berg, S. Marieke van Ham, Frank Baas, Ineke J.M. ten Berge, René A.W. van Lier
Human parvovirus B19 (B19V) is the only human pathogenic parvovirus. It causes a wide spectrum of human diseases, including fifth disease (erythema infectiosum) in children and pure red cell aplasia in immunocompromised patients. B19V is highly erythrotropic and preferentially replicates in erythroid progenitor cells (EPCs). Current understanding of how B19V interacts with cellular factors to regulate disease progression is limited, due to a lack of permissive cell lines and animal models. Here, we employed a recently developed primary human CD36+ EPC culture system that is highly permissive for B19V infection to identify cellular factors that lead to cell cycle arrest after B19V infection. We found that B19V exploited the E2F family of transcription factors by downregulating activating E2Fs (E2F1 to E2F3a) and upregulating repressive E2Fs (E2F4 to E2F8) in the primary CD36+ EPCs. B19V nonstructural protein 1 (NS1) was a key viral factor responsible for altering E2F1–E2F5 expression, but not E2F6–E2F8 expression. Interaction between NS1 and E2F4 or E2F5 enhanced the nuclear import of these repressive E2Fs and induced stable G2 arrest. NS1-induced G2 arrest was independent of p53 activation and increased viral replication. Downstream E2F4/E2F5 targets, which are potentially involved in the progression from G2 into M phase and erythroid differentiation, were identified by microarray analysis. These findings provide new insight into the molecular pathogenesis of B19V in highly permissive erythroid progenitors.
Zhihong Wan, Ning Zhi, Susan Wong, Keyvan Keyvanfar, Delong Liu, Nalini Raghavachari, Peter J. Munson, Su Su, Daniela Malide, Sachiko Kajigaya, Neal S. Young
Human cytomegalovirus (HCMV) in clinical material cannot replicate efficiently in vitro until it has adapted by mutation. Consequently, wild-type HCMV differ fundamentally from the passaged strains used for research. To generate a genetically intact source of HCMV, we cloned strain Merlin into a self-excising BAC. The Merlin BAC clone had mutations in the RL13 gene and UL128 locus that were acquired during limited replication in vitro prior to cloning. The complete wild-type HCMV gene complement was reconstructed by reference to the original clinical sample. Characterization of viruses generated from repaired BACs revealed that RL13 efficiently repressed HCMV replication in multiple cell types; moreover, RL13 mutants rapidly and reproducibly emerged in transfectants. Virus also acquired mutations in genes UL128, UL130, or UL131A, which inhibited virus growth specifically in fibroblast cells in wild-type form. We further report that RL13 encodes a highly glycosylated virion envelope protein and thus has the potential to modulate tropism. To overcome rapid emergence of mutations in genetically intact HCMV, we developed a system in which RL13 and UL131A were conditionally repressed during virus propagation. This technological advance now permits studies to be undertaken with a clonal, characterized HCMV strain containing the complete wild-type gene complement and promises to enhance the clinical relevance of fundamental research on HCMV.
Richard J. Stanton, Katarina Baluchova, Derrick J. Dargan, Charles Cunningham, Orla Sheehy, Sepehr Seirafian, Brian P. McSharry, M. Lynne Neale, James A. Davies, Peter Tomasec, Andrew J. Davison, Gavin W.G. Wilkinson
Persistent levels of IL-10 play a central role in progressive immune dysfunction associated with chronic viral infections such as HIV, but the underlying mechanisms are poorly understood. Because IL-10 affects the phenotypic and functional properties of DCs, which are responsible for initiating adaptive immune responses, we investigated whether IL-10 induces changes in DC phenotype and function in the context of HIV infection. Here, we show that IL-10 treatment of immature and mature human DCs in culture induced contrasting phenotypic changes in these populations: immature DCs exhibited aberrant resistance to NK cell–mediated elimination, whereas mature DCs exhibited increased susceptibility to NKG2D-dependent NK elimination. Treatment of immature and mature DCs with HIV resulted in potent IL-10 secretion and the same phenotypic and functional changes observed in the IL-10–treated cells. Consistent with these in vitro data, LNs isolated from individuals infected with HIV exhibited aberrant accumulation of a partially “immature” DC population. Together, these data suggest that the progressive immune dysfunction observed in chronic viral infections might be caused in part by IL-10–induced reversal of DC susceptibility to NK cell–mediated elimination, resulting in the accumulation of poorly immunogenic DCs in LNs, the sites of adaptive immune response induction.
Galit Alter, Daniel Kavanagh, Suzannah Rihn, Rutger Luteijn, David Brooks, Michael Oldstone, Jan van Lunzen, Marcus Altfeld
Viruses that infect T cells, including those of the lentivirus genus, such as HIV-1, modulate the responsiveness of infected T cells to stimulation by interacting APCs in a manner that renders the T cells more permissive for viral replication. HIV-1 and other primate lentiviruses use their Nef proteins to manipulate the T cell/APC contact zone, the immunological synapse (IS). It is known that primate lentiviral Nef proteins differ substantially in their ability to modulate cell surface expression of the TCR-CD3 and CD28 receptors critical for the formation and function of the IS. However, the impact of these differences in Nef function on the interaction and communication between virally infected T cells and primary APCs has not been investigated. Here we have used primary human cells to show that Nef proteins encoded by HIV-2 and most SIVs, which downmodulate cell surface expression of TCR-CD3, disrupt formation of the IS between infected T cells and Ag-presenting macrophages or DCs. In contrast, nef alleles from HIV-1 and its simian precursor SIVcpz failed to suppress synapse formation and events downstream of TCR signaling. Our data suggest that most primate lentiviruses disrupt communication between virally infected CD4+ Th cells and APCs, whereas HIV-1 and its SIV precursor have largely lost this capability. The resulting differences in the levels of T cell activation and apoptosis may play a role in the pathogenesis of AIDS.
Nathalie Arhel, Martin Lehmann, Karen Clauß, G. Ulrich Nienhaus, Vincent Piguet, Frank Kirchhoff
There is an association between expression of the MHC class I molecule HLA-B27 and protection following human infection with either HIV or HCV. In both cases, protection has been linked to HLA-B27 presentation of a single immunodominant viral peptide epitope to CD8+ T cells. If HIV mutates the HLA-B27–binding anchor of this epitope to escape the protective immune response, the result is a less-fit virus that requires additional compensatory clustered mutations. Here, we sought to determine whether the immunodominant HLA-B27–restricted HCV epitope was similarly constrained by analyzing the replication competence and immunogenicity of different escape mutants. Interestingly, in most HLA-B27–positive patients chronically infected with HCV, the escape mutations spared the HLA-B27–binding anchor. Instead, the escape mutations were clustered at other sites within the epitope and had only a modest impact on replication competence. Further analysis revealed that the cluster of mutations is required for efficient escape because a combination of mutations is needed to impair T cell recognition of the epitope. Artificially introduced mutations at the HLA-B27–binding anchors were found to be either completely cross-reactive or to lead to substantial loss of fitness. These results suggest that protection by HLA-B27 in HCV infection can be explained by the requirement to accumulate a cluster of mutations within the immunodominant epitope to escape T cell recognition.
Eva Dazert, Christoph Neumann-Haefelin, Stéphane Bressanelli, Karen Fitzmaurice, Julia Kort, Jörg Timm, Susan McKiernan, Dermot Kelleher, Norbert Gruener, John E. Tavis, Hugo R. Rosen, Jaqueline Shaw, Paul Bowness, Hubert E. Blum, Paul Klenerman, Ralf Bartenschlager, Robert Thimme
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