Given the ongoing SARS-CoV-2 pandemic, identification of immunogenic targets against the coronavirus spike glycoprotein will provide crucial advances towards the development of sensitive diagnostic tools and potential vaccine candidate targets. In this study, using pools of overlapping linear B-cell peptides, we report two IgG immunodominant regions on SARS-CoV-2 spike glycoprotein that are recognised by sera from COVID-19 convalescent patients. Notably, one is specific to SARS-CoV-2, which is located in close proximity to the receptor binding domain. The other region, which is localised at the fusion peptide, could potentially function as a pan-SARS target. Functionally, antibody depletion assays demonstrate that antibodies targeting these immunodominant regions significantly alter virus neutralisation capacities. Taken together, identification and validation of these neutralising B-cell epitopes will provide insights towards the design of diagnostics and vaccine candidates against this high priority coronavirus.

The mechanism of action of a serotype-specific natural human antibody against dengue virus has been identified.

Dengue virus (DENV) is the principal arthropod-borne viral pathogen afflicting human populations. While repertoires of antibodies to DENV have been linked to protection or enhanced infection, the role of T lymphocytes in these processes remains poorly defined. This study provides a comprehensive overview of CD4(+) and CD8(+) T cell epitope reactivities against the DENV 2 proteome in adult patients experiencing secondary DENV infection. Dengue virus-specific T cell responses directed against an overlapping 15mer peptide library spanning the DENV 2 proteome were analyzed ex vivo by enzyme-linked immunosorbent spot assay, and recognition of individual peptides was further characterized in specific T cell lines. Thirty novel T cell epitopes were identified, 9 of which are CD4(+) and 21 are CD8(+) T cell epitopes. We observe that whereas CD8(+) T cell epitopes preferentially target nonstructural proteins (NS3 and NS5), CD4(+) epitopes are skewed toward recognition of viral components that are also targeted by B lymphocytes (envelope, capsid, and NS1). Consistently, a large proportion of dengue virus-specific CD4(+) T cells have phenotypic characteristics of circulating follicular helper T cells (CXCR5 expression and production of interleukin-21 or gamma interferon), suggesting that they are interacting with B cells in vivo. This study shows that during a dengue virus infection, the protein targets of human CD4(+) and CD8(+) T cells are largely distinct, thus highlighting key differences in the immunodominance of DENV proteins for these two cell types. This has important implications for our understanding of how the two arms of the human adaptive immune system are differentially targeted and employed as part of our response to DENV infection.

). Most of them are scaffolding proteins that contain several structural interaction domains such as Src homology 2 (SH2) or 3 (SH3) domains, post-synapticdensity-95/disc-large/zonula-occludens-1 (PDZ) domains and Drosophila enabled and vasodilator-stimulated phosphoprotein homologous (EVH) domains. These proteins participate in the building of large submembrane protein signaling networks. We have recently isolated a complex of at least 15 proteins interacting with the C-terminal tail of the 5-HT2C receptor, using a proteomic approach combining peptide-affinity chromatography and mass spectrometry. This further supports the interaction of the GPCR C-terminus with large protein networks. Moreover, functional studies have established that the proteins that interact with the GPCR C-terminus are implicated in various GPCR functions that do not involve Gproteins. These functions include trafficking, targeting to specific subcellular compartments, clustering with effectors, fine tuning of G-protein activation and desensitization.

؊/؊ neurons, indicate that SNX27 may function to regulate endocytosis and/or endosomal sorting of NR2C. This is consistent with a role of SNX27 as a general regulator for sorting of membrane proteins containing a PDZ-binding motif, and its absence may alter the trafficking of these proteins, leading to growth and survival defects.

The uptake, transport, and presentation of Ags by lung dendritic cells (DCs) are central to the initiation of CD8 T cell responses against respiratory viruses. Although several studies have demonstrated a critical role of CD11blow/negCD103+ DCs for the initiation of cytotoxic T cell responses against the influenza virus, the underlying mechanisms for its potent ability to prime CD8 T cells remain poorly understood. Using a novel approach of fluorescent lipophilic dye-labeled influenza virus, we demonstrate that CD11blow/negCD103+ DCs are the dominant lung DC population transporting influenza virus to the posterior mediastinal lymph node as early as 20 h postinfection. By contrast, CD11bhighCD103neg DCs, although more efficient for taking up the virus within the lung, migrate poorly to the lymph node and remain in the lung to produce proinflammatory cytokines instead. CD11blow/negCD103+ DCs efficiently load viral peptide onto MHC class I complexes and therefore uniquely possess the capacity to potently induce proliferation of naive CD8 T cells. In addition, the peptide transporters TAP1 and TAP2 are constitutively expressed at higher levels in CD11blow/negCD103+ DCs, providing, to our knowledge, the first evidence of a distinct regulation of the Ag-processing pathway in these cells. Collectively, these results show that CD11blow/negCD103+ DCs are functionally specialized for the transport of Ag from the lung to the lymph node and also for efficient processing and presentation of viral Ags to CD8 T cells.

The interaction of antibodies, dengue virus (DENV), and monocytes can result in either immunity or enhanced virus infection. These opposing outcomes of dengue antibodies have hampered dengue vaccine development. Recent studies have shown that antibodies neutralize DENV by either preventing virus attachment to cellular receptors or inhibiting viral fusion intracellularly. However, whether the antibody blocks attachment or fusion, the resulting immune complexes are expected to be phagocytosed by Fc gamma receptor (FcγR)-bearing cells and cleared from circulation. This suggests that only antibodies that are able to block fusion intracellularly would be able to neutralize DENV upon FcγR-mediated uptake by monocytes whereas other antibodies would have resulted in enhancement of DENV replication. Using convalescent sera from dengue patients, we observed that neutralization of the homologous serotypes occurred despite FcγR-mediated uptake. However, FcγR-mediated uptake appeared to be inhibited when neutralized heterologous DENV serotypes were used instead. We demonstrate that this inhibition occurred through the formation of viral aggregates by antibodies in a concentration-dependent manner. Aggregation of viruses enabled antibodies to cross-link the inhibitory FcγRIIB, which is expressed at low levels but which inhibits FcγR-mediated phagocytosis and hence prevents antibody-dependent enhancement of DENV infection in monocytes. D engue is the most common mosquito-borne viral disease globally. The lack of an effective preventive measure, especially a licensed vaccine, has resulted in the global spread of this virus (1, 2). Although neutralizing antibodies can confer lifelong immunity against reinfection by one of the four dengue virus (DENV) serotypes, subneutralizing antibody levels or crossreactive antibodies appear to enhance the risk of severe dengue in subsequent infections (3-6). DENV bound with subneutralizing concentrations of antibody has been shown to result in increased virus uptake and replication in Fc gamma receptor (FcγR)-bearing cells such as monocytes/macrophages (4, 7). Thus, defining the determinants for virus neutralization will be important for the design of an effective dengue vaccine that protects against all four DENV serotypes while minimizing the risk of antibodydependent enhancement of DENV infection.Neutralization of flavivirus infection is a multiple-hit phenomenon. Recent stoichiometric studies have shown that both antibody affinity and epitope accessibility are important determinants for virus neutralization (8-10). Antibodies neutralize DENV by either preventing virus attachment to cellular receptors (11) or inhibiting viral fusion intracellularly (12). However, whether the antibody blocks attachment or fusion, the resulting immune complex is expected to be cleared from the circulation by professional phagocytes, especially the FcγR-bearing cells. This suggests that only antibodies that are able to block fusion intracellularly would be able to neutralize DENV upon FcγR-mediated uptake by ...

Viruses must evade the host innate defenses for replication and dengue is no exception. During secondary infection with a heterologous dengue virus (DENV) serotype, DENV is opsonized with sub-or nonneutralizing antibodies that enhance infection of monocytes, macrophages, and dendritic cells via the Fc-gamma receptor (FcγR), a process termed antibody-dependent enhancement of DENV infection. However, this enhancement of DENV infection is curious as cross-linking of activating FcγRs signals an early antiviral response by inducing the type-I IFN-stimulated genes (ISGs). Entry through activating FcγR would thus place DENV in an intracellular environment unfavorable for enhanced replication. Here we demonstrate that, to escape this antiviral response, antibody-opsonized DENV coligates leukocyte Ig-like receptor-B1 (LILRB1) to inhibit FcγR signaling for ISG expression. This immunoreceptor tyrosine-based inhibition motif-bearing receptor recruits Src homology phosphatase-1 to dephosphorylate spleen tyrosine kinase (Syk). As Syk is a key intermediate of FcγR signaling, LILRB1 coligation resulted in reduced ISG expression for enhanced DENV replication. Our findings suggest a unique mechanism for DENV to evade an early antiviral response for enhanced infection.early innate immune response | innate immune signaling | immune evasion D espite long-lived serotype-specific immunity upon initial infection, predicted global prevalence of dengue now surpasses World Health Organization estimates by more than threefold with 390 million cases annually (1). Furthermore, the risk of severe disease is augmented by cross-reactive or subneutralizing levels of antibody (2, 3), which opsonize dengue virus (DENV) to ligate Fc-gamma receptor (FcγR) for entry into monocytes, macrophages, and dendritic cells, a phenomenon known as antibody-dependent enhancement (ADE) of DENV infection (4, 5). The resultant greater viral burden leads to increased systemic inflammation that precipitates plasma leakage, a hallmark of dengue hemorrhagic fever (6). However, ligation of the activating FcγRs by immune complexes has been shown to induce type-I IFN stimulated genes (ISGs), independent of autocrine or paracrine IFN activity, unless the inhibitory FcγRIIB is coligated (7). We and others reported recently that coligation of FcγRIIB by DENV immune complexes requires high antibody concentration, and such coligation inhibited the entry of DENV immune complexes into monocytes (8, 9). At low antibody concentrations where ADE occurs, the inhibitory FcγRIIB is not coligated (9). Ligation of the activating FcγRs by DENV opsonized with subneutralizing levels of antibody would thus induce the expression of ISGs and hinder DENV replication (10). Here, we demonstrate that DENV employs a unique evasive mechanism by coligating LILRB1 to down-regulate the early antiviral responses triggered by activating FcγRs for ADE.Results ADE Differs in THP-1 Subclones. Our work was enabled by the isolation of subclones of THP-1 cells with different phenotypes to ADE. The low rate of...