Masashi Shingai

Subcellular Localization of Toll-Like Receptor 3 in Human Dendritic Cells

Toll-like receptor (TLR)3 recognizes dsRNA and transduces signals to activate NF-κB and IFN-β promoter. Type I IFNs (IFN-α/β) function as key cytokines in anti-viral host defense. Human fibroblasts express TLR3 on the cell surface, and anti-TLR3 mAb inhibits dsRNA-induced IFN-β secretion by fibroblasts, suggesting that TLR3 acts on the cell surface to sense viral infection. In this study, we examined the expression and localization of human TLR3 in various DC subsets using anti-TLR3 mAb. In monocyte-derived immature dendritic cells (iDCs), TLR3 predominantly resided inside the cells but not on the cell surface. iDCs produced IL-12p70 and IFN-α and -β in response to poly(I:C). Similar response was observed in iDCs treated with rotavirus-derived dsRNA. These responses could not be blocked by pretreatment of the cells with anti-TLR3 mAb. In CD11c+ blood DCs, cytoplasmic retention of TLR3 was also observed as in monocyte-derived iDCs, again endorsing a different TLR3 distribution profile from fibroblasts. In precursor DC2, however, TLR3 could not be detected inside or outside the cells. Of note, there was a putative centrosomal protein that shared an epitope with TLR3 in myeloid DCs and precursor DC2, but not peripheral blood monocytes. Immunoelectron microscopic analysis revealed that TLR3, when stably expressed in the murine B cell line Ba/F3, was specifically accumulated in multivesicular bodies, a subcellular compartment situated in endocytic trafficking pathways. Thus, regulation and localization of TLR3 are different in each cell type, which may reflect participation of cell type-specific multiple pathways in antiviral IFN induction via TLR3.

Antibody-mediated immunotherapy of macaques chronically infected with SHIV suppresses viraemia

Neutralizing antibodies can confer immunity to primate lentiviruses by blocking infection in macaque models of AIDS. However, earlier studies of anti-human immunodeficiency virus type 1 (HIV-1) neutralizing antibodies administered to infected individuals or humanized mice reported poor control of virus replication and the rapid emergence of resistant variants. A new generation of anti-HIV-1 monoclonal antibodies, possessing extraordinary potency and breadth of neutralizing activity, has recently been isolated from infected individuals. These neutralizing antibodies target different regions of the HIV-1 envelope glycoprotein including the CD4-binding site, glycans located in the V1/V2, V3 and V4 regions, and the membrane proximal external region of gp41 (refs 9, 10, 11, 12, 13, 14). Here we have examined two of the new antibodies, directed to the CD4-binding site and the V3 region (3BNC117 and 10-1074, respectively), for their ability to block infection and suppress viraemia in macaques infected with the R5 tropic simian–human immunodeficiency virus (SHIV)-AD8, which emulates many of the pathogenic and immunogenic properties of HIV-1 during infections of rhesus macaques. Either antibody alone can potently block virus acquisition. When administered individually to recently infected macaques, the 10-1074 antibody caused a rapid decline in virus load to undetectable levels for 4–7 days, followed by virus rebound during which neutralization-resistant variants became detectable. When administered together, a single treatment rapidly suppressed plasma viraemia for 3–5 weeks in some long-term chronically SHIV-infected animals with low CD4+ T-cell levels. A second cycle of anti-HIV-1 monoclonal antibody therapy, administered to two previously treated animals, successfully controlled virus rebound. These results indicate that immunotherapy or a combination of immunotherapy plus conventional antiretroviral drugs might be useful as a treatment for chronically HIV-1-infected individuals experiencing immune dysfunction.

Antitumor NK activation induced by the Toll-like receptor 3-TICAM-1 (TRIF) pathway in myeloid dendritic cells

Myeloid dendritic cells (mDCs) recognize and respond to polyI:C, an analog of dsRNA, by endosomal Toll-like receptor (TLR) 3 and cytoplasmic receptors. Natural killer (NK) cells are activated in vivo by the administration of polyI:C to mice and in vivo are reciprocally activated by mDCs, although the molecular mechanisms are as yet undetermined. Here, we show that the TLR adaptor TICAM-1 (TRIF) participates in mDC-derived antitumor NK activation. In a syngeneic mouse tumor implant model (C57BL/6 vs. B16 melanoma with low H-2 expresser), i.p. administration of polyI:C led to the retardation of tumor growth, an effect relied on by NK activation. This NK-dependent tumor regression did not occur in TICAM-1−/− or IFNAR−/− mice, whereas a normal NK antitumor response was induced in PKR−/−, MyD88−/−, IFN-β−/−, and wild-type mice. IFNAR was a prerequisite for the induction of IFN-α/β and TLR3. The lack of TICAM-1 did not affect IFN production but resulted in unresponsiveness to IL-12 production, mDC maturation, and polyI:C-mediated NK-antitumor activity. This NK activation required NK-mDC contact but not IL-12 function in in vivo transwell analysis. Implanted tumor growth in IFNAR−/− mice was retarded by adoptively transferring polyI:C-treated TICACM-1-positive mDCs but not TICAM-1−/− mDCs. Thus, TICAM-1 in mDCs critically facilitated mDC-NK contact and activation of antitumor NK, resulting in the regression of low MHC-expressing tumors.

Passive transfer of modest titers of potent and broadly neutralizing anti-HIV monoclonal antibodies block SHIV infection in macaques

Five potent and broadly anti-HIV neutralizing monoclonal antibodies are able to block infection by two different SHIVs in monkeys. The authors show that antibodies targeting the outer glycan coat were the most effective and determined that titers of roughly 1:100 protected half the animals.

NAK-Associated Protein 1 Participates in Both the TLR3 and the Cytoplasmic Pathways in Type I IFN Induction

TLR3 and the cytoplasmic helicase family proteins (retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated gene 5 (MDA5)) serve as dsRNA pattern-recognition receptors. In response to poly(I:C), a representative of dsRNA, and viral infection, they have been shown to activate the transcription factor IFN regulatory factor (IRF)-3, which in turn induces activation of the IFN-β promoter. RIG-I/MDA5 recognizes dsRNA in the cytoplasm, whereas TLR3 resides in the cell surface membrane or endosomes to engage in extracytoplasmic recognition of dsRNA. Recent reports suggest that TLR3 induces cellular responses in epithelial cells in response to respiratory syncytial virus (RSV). The modus for TLR3 activation by RSV, however, remains unresolved. By small interference RNA gene-silencing technology and human cell transfectants, we have revealed that knockdown of NAK-associated protein 1 (NAP1) leads to the down-regulation of IFN-β promoter activation >24 h after poly(I:C) or virus (RSV and vesicular stomatitis virus) treatment. NAP1 is located downstream of the adapter Toll-IL-1R homology domain-containing adapter molecule (TICAM)-1 (Toll/IL-1R domain-containing adapter-inducing IFN-β) in the TLR3 pathway, but TICAM-1 and TLR3 did not participate in the IRF-3 and IFN-β promoter activation by RSV infection. Virus-mediated activation of the IFN-β promoter was largely abrogated by the gene silencing of IFN-β promoter stimulator-1 (mitochondria antiviral signaling (MAVS), VISA, Cardif), the adapter of the RIG-I/MDA5 dsRNA-recognition proteins. In both the TLR and virus-mediated IFN-inducing pathways, IκB kinase-related kinase ε and TANK-binding kinase 1 participated in IFN-β induction. Thus, RSV as well as other viruses induces replication-mediated activation of the IFN-β promoter, which is intracellularly initiated by the RIG-I/MDA5 but not the TLR3 pathway. Both the cytoplasmic and TLR3-mediated dsRNA recognition pathways converge upon NAP1 for the activation of the IRF-3 and IFN-β promoter.

Differential type I IFN-inducing abilities of wild-type versus vaccine strains of measles virus.

Laboratory adapted and vaccine strains of measles virus (MV) induced type I IFN in infected cells. The wild-type strains in contrast induced it to a far lesser extent. We have investigated the mechanism for this differential type I IFN induction in monocyte-derived dendritic cells infected with representative MV strains. Laboratory adapted strains Nagahata and Edmonston infected monocyte-derived dendritic cells and activated IRF-3 followed by IFN-β production, while wild-type MS failed to activate IRF-3. The viral IRF-3 activation is induced within 2 h, an early response occurring before protein synthesis. Receptor usage of CD46 or CD150 and nucleocapsid (N) protein variations barely affected the strain-to-strain difference in IFN-inducing abilities. Strikingly, most of the IFN-inducing strains possessed defective interference (DI) RNAs of varying sizes. In addition, an artificially produced DI RNA consisting of stem (the leader and trailer of MV) and loop (the GFP sequence) exhibited potential IFN-inducing ability. In this case, however, cytoplasmic introduction was needed for DI RNA to induce type I IFN in target cells. By gene-silencing analysis, DI RNA activated the RIG-I/MDA5-mitochondria antiviral signaling pathway, but not the TLR3-TICAM-1 pathway. DI RNA-containing strains induced IFN-β mRNA within 2 h while the same recombinant strains with no DI RNA required >12 h postinfection to attain similar levels of IFN-β mRNA. Thus, the stem-loop structure, rather than full genome replication or specific internal sequences of the MV genome, is required for an early phase of type I IFN induction by MV in host cells.

Dendritic Cell Maturation Induced by Muramyl Dipeptide (MDP) Derivatives: Monoacylated MDP Confers TLR2/TLR4 Activation

6-O-acyl-muramyldipeptides (MDP) with various lengths of fatty acid chains were examined for their dendritic cell (DC) maturation activity expressed through TLRs. Judging from anti-TLR mAb/inhibitor-blocking analysis, MDP derivatives with a single octanoyl or stearoyl fatty acid chain were found to activate TLR2 and TLR4 on human DCs, although intact and diacylated MDP expressed no ability to activate TLRs. Human DC activation profiles by the monoacylated MDP were essentially similar to those by Calmette-Guérin (BCG)-cell wall skeleton (CWS) and BCG-peptidoglycan (PGN) based on their ability to up-regulate costimulators, HLA-DR, β2-microglobulin, and allostimulatory MLR. Monoacylated MDP induced cytokines with similar profiles to BCG-CWS or -PGN, although their potency for induction of TNF-α, IL-12p40, and IL-6 was less than that of BCG-CWS or -PGN. The MDP derivatives initiated similar activation in normal mouse macrophages, but exhibited no effect on TLR2/4-deficient or MyD88-deficient mouse macrophages. Mutation of d-isoGln to l-isoGln in monoacylated MDP did not result in loss of the DC maturation activity, suggesting marginal participation of nucleotide-binding oligomerization domain 2, if any, in monoacyl MDP-dependent DC maturation. These results define the adjuvant activity of 6-O-acyl MDP compounds at the molecular level. They target TLR2/TLR4 and act through the MyD88-dependent pathway in DCs and macrophages. Hence, the unusual combined activation of TLR2 and TLR4 observed with Mycobacterium tuberculosis is in part reflected in the functional properties of monoacylated MDP compounds. These findings infer that the essential minimal requirement for TLR2/4-mediated adjuvancy of BCG lies within a modified MDP.

Rapid development of glycan-specific, broad, and potent anti–HIV-1 gp120 neutralizing antibodies in an R5 SIV/HIV chimeric virus infected macaque

It is widely believed that the induction of a broadly neutralizing antibody (bNAb) response will be a critical component of a successful vaccine against HIV. A significant fraction of HIV-infected individuals mount bNAb responses, providing support for the notion that such responses could be elicited through vaccination. Infection of macaques with simian immunodeficiency virus (SIV) or SIV/HIV chimeric virus (SHIV) has been widely used to model aspects of HIV infection, but to date, only limited bNAb responses have been described. Here, we screened plasma from 14 R5-tropic SHIV-infected macaques for broadly neutralizing activity and identified a macaque with highly potent cross-clade plasma NAb response. Longitudinal studies showed that the development of broad and autologous NAb responses occurred coincidentally in this animal. Serum-mapping studies, using pseudovirus point mutants and antigen adsorption assays, indicated that the plasma bNAbs are specific for epitopes that include carbohydrates and are critically dependent on the glycan at position 332 of Env gp120. The results described herein provide insight into the development and evolution of a broad response, suggest that certain bNAb specificities may be more rapidly induced by immunization than others, and provide a potential model for the facile study of the development of bNAb responses.

Hepatitis C virus–infected hepatocytes extrinsically modulate dendritic cell maturation to activate T cells and natural killer cells

Dendritic cell maturation critically modulates antiviral immune responses, and facilitates viral clearance. Hepatitis C virus (HCV) is characterized by its high predisposition to persistent infection. Here, we examined the immune response of human monocyte‐derived dendritic cells (MoDCs) to the JFH1 strain of HCV, which can efficiently replicate in cell culture. However, neither HCV RNA replication nor antigen production was detected in MoDCs inoculated with JFH1. None of the indicators of HCV interacting with MoDCs we evaluated were affected, including expression of maturation markers (CD80, 83, 86), cytokines (interleukin‐6 and interferon‐beta), the mixed lymphocyte reaction, and natural killer (NK) cell cytotoxicity. Strikingly, MoDCs matured by phagocytosing extrinsically‐infected vesicles containing HCV‐derived double‐stranded RNA (dsRNA). When MoDCs were cocultured with HCV‐infected apoptotic Huh7.5.1 hepatic cells, there was increased CD86 expression and interleukin‐6 and interferon‐beta production in MoDCs, which were characterized by the potential to activate NK cells and induce CD4+ T cells into the T helper 1 type. Lipid raft‐dependent phagocytosis of HCV‐infected apoptotic vesicles containing dsRNA was indispensable to MoDC maturation. Colocalization of dsRNA with Toll‐like receptor 3 (TLR3) in phagosomes suggested the importance of TLR3 signaling in the MoDC response against HCV. Conclusion: The JFH1 strain does not directly stimulate MoDCs to activate T cells and NK cells, but phagocytosing HCV‐infected apoptotic cells and their interaction with the TLR3 pathway in MoDCs plays a critical role in MoDC maturation and reciprocal activation of T and NK cells. (HEPATOLOGY 2008.)

Wild-Type Measles Virus Infection in Human CD46/CD150-Transgenic Mice: CD11c-Positive Dendritic Cells Establish Systemic Viral Infection

We generated transgenic (TG) mice that constitutively express human CD46 (huCD46) and/or TLR-inducible CD150 (huCD150), which serve as receptors for measles virus (MV). These mice were used to study the spreading and pathogenicity of GFP-expressing or intact laboratory-adapted Edmonston and wild-type Ichinose (IC) strains of MV. Irrespective of the route of administration, neither type of MV was pathogenic to these TG mice. However, in ex vivo, limited replication of IC was observed in the spleen lymphocytes from huCD46/huCD150 TG and huCD150 TG, but not in huCD46 TG and non-TG mice. In huCD150-positive TG mouse cells, CD11c-positive bone marrow-derived myeloid dendritic cells (mDC) participated in MV-mediated type I IFN induction. The level and induction profile of IFN-β was higher in mDC than the profile of IFN-α. Wild-type IC induced markedly high levels of IFN-β compared with Edmonston in mDC, as opposed to human dendritic cells. We then generated huCD46/huCD150 TG mice with type I IFN receptor (IFNAR1)−/− mice. MV-bearing mDCs spreading to draining lymph nodes were clearly observed in these triple mutant mice in vivo by i.p. MV injection. Infectious lymph nodes were also detected in the double TG mice into which MV-infected CD11c-positive mDCs were i.v. transferred. This finding suggests that in the double TG mouse model mDCs once infected facilitate systemic MV spreading and infection, which depend on mDC MV permissiveness determined by the level of type I IFN generated via IFNAR1. Although these results may not simply reflect human MV infection, the huCD150/huCD46 TG mice may serve as a useful model for the analysis of MV-dependent modulation of mDC response.