PLoS Pathogens最新文献

Of the seven serotypes of foot-and-mouth disease virus (FMDV) strains circulating globally, serotype Asia1 has been effectively eradicated in China through systematic vaccination in livestock. The structural characteristics of serotype Asia1 may enhance its immunogenicity compared to other serotypes. Herein, we present a preliminary exploration of Asia1-binding B-cell receptor repertoire, containing 3571 clones, and identified 17 porcine-derived neutralizing monoclonal antibodies (pnAbs) from the top 33 high-frequency clonotypes. The majority of pnAbs (14/17) recognized the epitopes on VP2, with a common determinant at residue 72 (D) on the B-C loop; two pnAbs (2/17) recognized a novel epitope spanning VP2 and VP3; and the remaining one (1/17) bound to the C-terminus of VP1. Furthermore, the antigenic structures on VP2 and spanning VP2 and VP3 were respectively elucidated by determining the cryo-EM structures of FMDV serotype Asia1 in complexes with two pnAbs, PAS5 and PAS12. The light chain of PAS5, forming the majority of contact sites with the viral particle, focuses on the βB, B-C loop, βC and H-I loop of VP2, with key determinants at residues 68, 72 and 77 around the three-fold axis, corresponding to antigenic site 2. The contact sites of both VH and VL of PAS12 uncover a novel antigenic structure comprising the B-C, and H-I loops on VP2, and the B-B knob and βB on VP3, with key determinants at residue 73 on VP2 and 59 on VP3. Subsequently, site-directed competitive ELISA analysis of sera from primary and booster vaccinated pigs revealed a balanced antibody response profile, suggesting a potentially even immunodominance among antigenic site 2, VP1 G-H loop, and the novel antigenic structure spanning VP2 and VP3 on FMDV serotype Asia1. Compared to the focused immunodominance observed in other serotypes, this balanced antigenic recognition across VP1, VP2, and VP3 of FMDV serotype Asia1 reflects a diversified antibody response that may contribute to effective neutralization and protection.

B cells play a crucial role in humoral immunity, acting as sentinels against viral infections by using their B cell receptors (BCRs) to recognize viral proteins. This recognition typically triggers a response leading to the production of neutralizing antibodies against viral surface proteins, such as the viral envelope proteins. However, recent studies have revealed a surprising dual role for BCRs, showing that some enveloped viruses and viral vectors, such as Dengue virus and lentiviral vectors, can exploit anti-viral BCRs as their attachment and entry receptors to infect/transduce B cells. While these viruses use a simple low-pH-dependent fusion mechanism for entry, it remained unclear whether BCRs could facilitate the entry of viruses with more complex fusion requirements, such as HIV-1 and SARS-CoV-2, which rely on their cognate receptors to activate their fusion machinery. In this study, we investigated the ability of BCRs to mediate viral entry for HIV-1 and SARS-CoV-2, which require specific host receptors (CD4 and ACE2, respectively) to activate their fusion machinery. We found that while anti-HIV-1 envelope protein BCRs can mediate viral attachment, they are unable to facilitate viral fusion and entry. In contrast, anti-SARS-CoV-2 Spike (S) protein BCRs not only mediate attachment but also enable viral entry in the absence of the ACE2 receptor. Our findings demonstrate that the ability of anti-viral BCRs to mediate viral fusion/entry is not universal but depends on the specific viral envelope protein. This novel entry pathway has important implications for both viral replication and the development of B cell-mediated immunity.

Human cytomegalovirus (HCMV) poses a significant risk to immunocompromised individuals and is the leading cause of congenital birth defects worldwide. There is no cure or robust treatment options, although neutralizing antibodies (nAbs) derived from patient sera are being explored as prophylactics with limited success. Glycoprotein B (gB) is a viral membrane fusogen and a major target of the anti-HCMV humoral response in humans. Here, we engineered a soluble, prefusion-stabilized HCMV gB ectodomain variant and used it to isolate twelve new human monoclonal antibodies (mAbs). Seven of these mAbs strongly neutralized at least one strain of HCMV in vitro, whereas six mAbs neutralized both lab-adapted and minimally passaged clinical strains (were broadly neutralizing, bnAbs). All nAbs bound different epitopes within antigenic regions AD-4 or AD-5, and most targeted new sites. Despite being isolated using prefusion-stabilized HCMV gB variant, nAbs varied in their conformational specificity. Only one nAb preferentially bound the prefusion form, and most preferentially bound the intermediate form. The seven nAbs were separated into three classes based on their putative neutralization mechanisms, which were deduced from their conformational specificity, reactivity with gB on the cell surface, and epitope location. Our stabilized prefusion-gB construct provides a tool for isolating potent new nAbs, including prefusion-specific ones, and studying HCMV immunogenicity. Long term, these potent nAbs that arose during natural infections could be developed into potent prophylactics and therapeutics against HCMV diseases.

The receptor-binding protein of influenza A virus, hemagglutinin (HA), is the most abundant protein on the viral surface. While high densities of HA are thought to improve cellular attachment by increasing avidity for the viral receptor, they may also increase the avidity of neutralizing antibodies. The tradeoff between these two competing effects of avidity is not well understood. To better understand how features of the viral surface influence antibody avidity, we developed fluorescence-based assays to measure dissociation kinetics and steady-state binding of antibodies to intact virions. Focusing on two antibodies that bind to the HA head domain (S139/1 and C05), we confirm that binding orientations that favor bivalent attachment of antibodies to the viral surface can offset weak monovalent affinity by facilitating crosslinking. By modulating HA density in both engineered viruses and synthetic nanoparticles, we find that bivalent antibody binding remains resilient down to one-tenth the HA density on the viral surface and, in the case of C05, that antibody occupancy increases at these lowest densities. Finally, using a combination of structure-guided modeling and antibodies that lock HA in a tilted conformation, we identify flexibility of the HA ectodomain as an additional determinant of antibody avidity. Together, these results establish features of the viral surface that help support or suppress the binding of neutralizing antibodies.

Lysophagy plays a key role in maintaining autophagy homeostasis, but the induction and regulation mechanisms of lysophagy are not clear. In this study, we found that Senecavirus A (SVA) dramatically decreased lysosomal-associated membrane protein 1(LAMP1), significantly increased lysosomal permeability, and induced lysophagy. We demonstrated that the SO2 probe (2-(4-(dimethylamino-) phenyl)1,1, 3-trimethyl-1h-benzo [e] indole-3-ium, DLC) could inhibited the degradation of LAMP1 and reduced lysophagy caused by SVA infection. DLC directly binds to LAMP1, and enhanced sulfenylation modification of LAMP1 at Cys375 to inhibit non-lysine ubiquitination. Finally, we verified the antiviral effects of DLC in cells and in BALB/c mice. Taken together, our study lays the foundation for the identification of SVA infection targets and the development of antiviral drugs in the future.

Gamma delta (γδ) T cells are important mediators of the immune response to childhood malaria. Human Vγ9+Vδ2+ T cells possess intrinsic, HLA-independent responsiveness to Plasmodium falciparum phosphoantigens produced in the blood stage of malaria. Engagement of the γδ T cell receptor (TCR) by phosphoantigen-bound butyrophilin molecules results in Vγ9+Vδ2+ T cell expansion, pro-inflammatory cytokine production, and release of cytotoxic granules that mediate parasite killing. Repeated P. falciparum infection, however, leads to a reduction in circulating Vγ9+Vδ2+ T cells and upregulation of immunomodulatory molecules, including NK receptors, that correlates with less severe symptoms upon infection. We explore phenotypic and functional differences of γδ T cells in Ugandan children with high versus low malaria exposure, utilizing high-parameter spectral flow cytometry analysis of PBMCs. We observed significant differences in expression of inhibitory NK receptors - KIR2DL1, KIR2DL2/3, KIR3DL1, LILRB1, and NKG2A - on γδ T cell subsets, with Vγ9+Vδ2+ T cells exhibiting a divergent mechanism of control compared to other subsets. We found that NKG2A and KIR3DL1 expression associated with potent Vγ9+Vδ2+ T cell responses to TCR- and Fc receptor (FcR)-mediated stimulation while KIR2DL1, KIR2DL2/3 and LILRB1 associated with reduced degranulation and cytokine production. These results identify a new role for inhibitory NK receptors expressed on γδ T cells, exerting a finely tuned balance of activating and inhibitory signals to regulate the response to malaria-related antigens.

Middle East respiratory syndrome coronavirus (MERS-CoV) is an emerging coronavirus that can cause zoonotic disease in humans with lethal severe viral pneumonia. Dromedary camels are the source of zoonotic infection. As of November 2025, MERS-CoV has resulted in a total of 2630 reported cases, 37% of these being fatal. The number of reported human cases has been on a decreasing trend since 2016 and reached a nadir during the COVID-19 pandemic. The reason for the reduction of cases is unclear and may be multifactorial. We hypothesized that mutations accumulating in the virus spike protein may have reduced zoonotic potential. Here, we investigate the impact of recently emerged virus spike-protein mutations on virus replication competence using pseudoviruses and replication-competent recombinant viruses. We found that virus spike variants detected in 2019 and some from 2023 show a reduced cell entry, lower viral replication and reduced fitness in human primary alveolar epithelial cells and multiple cell lines. All the MERS-CoV spikes tested showed a cell-entry pathway preference via the cell-surface TMPRSS2 route. Mechanistically, we showed the V530A mutation in the 2019 spike sequence had a reduced human DPP4 binding phenotype. Our data highlighted MERS-CoV spike mutations can modulate viral fitness in human cells and provide new insights to understand recent MERS epidemiology.

Epigenetic suppression and durable silencing of HIV represent a promising strategy to achieve ART-free remission, consistent with the "block and lock" HIV cure paradigm. BRD4 is a host epigenetic reader and plays a critical role in HIV transcriptional regulation. We previously identified ZL0580, a first-in-class BRD4-selective small molecule distinct from the pan-BET inhibitor JQ1, which induces HIV epigenetic suppression. However, detailed molecular mechanisms, pharmacokinetics (PK), and in vivo HIV-suppressive efficacy of ZL0580 remain undefined. Here, we show that ZL0580 selectively targets BRD4 bromodomain 1 (BD1) through interaction with a key glutamic acid residue (E151), as determined by structural modeling and mutagenesis. Transcriptomic profiling by RNA-seq reveals that ZL0580 and JQ1 induce opposing gene expression programs, consistent with their distinct effects on HIV proviral transcription and latency. In a humanized mouse model of HIV infection, ZL0580 monotherapy, or in combination with ART, potently suppressed active HIV replication, reducing the plasma viremia to nearly undetectable levels, and delayed viral rebound following treatment interruption. Collectively, these findings establish ZL0580 as an epigenetic suppressor of HIV in vivo and provide proof-of-concept for its potential as a "block and lock" HIV cure candidate, warranting further optimization and development.