PLOS Pathogens

It’s not me, it’s you: Anti-phage nuclease specificity inside a bacterium

2026-02-13T14:00:00Z

by Alex Hong, Joseph Bondy-Denomy

Csep1^P protein from Campylobacter concisus induces a chemokine-dominant inflammatory state in macrophages and enhances proinflammatory response to gut bacteria

2026-02-13T14:00:00Z

by Christopher Yau Man Luk, Mohammad M. Rahman, Xiaotian Zhou, C. Mee Ling Munier, Fang Liu, Stephen M. Riordan, Anna Roujeinikova, Li Zhang

Translocation of Campylobacter concisus from the oral cavity to the intestinal tract is increasingly recognised as a contributor to inflammatory bowel disease (IBD). The C. concisus secreted protein Csep1 has emerged as a molecular marker of C. concisus strains associated with Crohn’s disease, a form of IBD. However, its structure and role in inflammation remain unknown. Here, we report the X-ray crystal structure of plasmid-encoded Csep1^P that reveals a unique α-helical fold with structural similarity to Helicobacter pylori cysteine-rich proteins HcpB and HcpC. Because HcpA, another Hcp family member, is known to affect monocyte differentiation, this structural similarity led us to hypothesise that Csep1^P may modulate monocyte differentiation and macrophage function. Transcriptomic analysis revealed that Csep1^P induced a chemokine-dominant inflammatory state in macrophages, M1-chem. Protein-level validation in both THP-1-derived and primary human macrophages confirmed this selective chemokine response. While Csep1^P alone did not upregulate proinflammatory cytokines, THP-1-derived macrophages pre-incubated with Csep1^P produced a higher level of proinflammatory cytokines in response to commensal Escherichia coli, which was validated on primary human macrophages. Furthermore, silencing the delta like canonical notch ligand 4 (DLL4) gene decreased the proinflammatory response of Csep1^P-mediated macrophages to E. coli. Collectively, our data demonstrate that the structurally unique Csep1^P reprograms macrophage response, which provides a mechanistic link between C. concisus infection and Crohn’s disease pathogenesis, and identifies Csep1^P as a potential target for therapeutic intervention.

A type III secretion system is required for Bordetella atropi invasion of host cells in vivo

2026-02-13T14:00:00Z

by Tuan D. Tran, Serena J. Meadows-Graves, Amanda R. Haio, Alexander I. Varga, Robert J. Luallen

Bordetella atropi is an intracellular bacterial pathogen that infects the intestinal epithelia of the nematode host Oscheius tipulae. We previously showed that the bacteria use filamentation as a novel cell-to-cell spreading mechanism once inside the intestinal cell. However, how the bacteria invade the host cells and what factors contribute to B. atropi infection process remain unknown. In this study, we investigate the roles of type III (T3SS) and type VI secretion systems (T6SS) in B. atropi pathogenesis, which are employed by many bacterial pathogens, both extracellular and intracellular, to deliver effectors that manipulate host physiology to their advantage. We found that the two T6SSs encoded in B. atropi genome played no obvious roles in the invasion or intracellular spreading. In contrast, a T3SS was required for intestinal cell invasion. T3SS mutants showed loss of host cell protrusions from the apical surface that normally engulf invading wild type bacteria, as seen by both electron microscopy and confocal fluorescent microscopy. These protrusions bear morphological similarities to membrane ruffles triggered by the T3SS-mediated invasion seen in other pathogens such as Salmonella and Shigella spp. Additionally, we conducted dual transcriptomics and saw upregulation of T3SS in vivo, along with several putative effectors and the virulence regulator BvgS of the genus Bordetellae. We knocked out these effector candidates and found that deletion of one of these genes, deiA (decreased invasion protein A), leads to a reduction in the number of invasion events and overall percentage of infected animals in the population. In addition, deletion of the virulence regulator bvgS resulted in a complete loss of B. atropi invasion, suggesting it may regulate T3SS for host cell invasion.

The UBC/SIRT5/DRP1 axis regulates mitochondrial dynamics to alleviate Staphylococcus aureus-induced oxidative stress and senescence in bovine mammary epithelial cells

2026-02-12T14:00:00Z

by Huijie Hu, Naiyuan Jiang, Juxiong Liu, Junlong Bi, Xuanting Liu, Bin Xu, Yu Cao, Wenjin Guo, Shoupeng Fu

Staphylococcus aureus (S. aureus)–driven senescence of bovine mammary epithelial cells is a key determinant of mammary gland health, yet its molecular basis remains poorly defined. Sirtuin 5 (SIRT5), a mitochondria-localized desuccinylase, may play an important regulatory role in this process. This study aimed to elucidate the mechanisms by which S. aureus drives cellular senescence and to define the contribution of the SIRT5–mitochondrial axis to delaying senescence. We found pronounced oxidative stress and cellular senescence in mammary tissues from cows with S. aureus mastitis, accompanied by marked downregulation of SIRT5. In an S. aureus-infected epithelial cell model, infection induced mitochondrial stress characterized by excessive mitochondrial fragmentation, loss of membrane potential, and increased mitochondrial superoxide, along with oxidative damage and cellular senescence. Mechanistically, S. aureus toxins and the toxin-induced inflammatory response cooperatively drove mitochondrial stress, which in turn increased intracellular bacterial burden and exacerbated cell death. During infection, SIRT5 protein abundance was significantly reduced. Mass spectrometry and co-immunoprecipitation analyses indicated that infection upregulated the ubiquitin-conjugating enzyme ubiquitin C (UBC), enhanced its interaction with SIRT5, and promoted ubiquitin-mediated degradation of SIRT5. Loss of SIRT5 increased succinylation of dynamin-related protein 1 (DRP1), inhibited its ubiquitin-mediated degradation, and led to its excessive accumulation on the outer mitochondrial membrane, thereby promoting excessive mitochondrial fission. Functionally, SIRT5 overexpression markedly alleviated mitochondrial stress, oxidative damage, and senescence phenotypes. When mitochondrial fission was forcibly enhanced, the cytoprotective effect of SIRT5 was substantially weakened, confirming that SIRT5 acts through a pathway dependent on mitochondrial integrity. Collectively, S. aureus infection releases toxins and induces inflammatory injury, during which UBC-mediated SIRT5 degradation activates DRP1-dependent mitochondrial hyper-fragmentation, aggravating mitochondrial stress, oxidative stress, and mammary epithelial cell senescence. These findings identify SIRT5 as a critical regulator of redox and mitochondrial homeostasis in mammary epithelial cells and a potential therapeutic target for mitigating oxidative damage associated with bovine mastitis.

Identification of multiple Acinetobacter baumannii protein antigens as targets for potential immunotherapies using a novel protein microarray screening approach

2026-02-12T14:00:00Z

by Samantha Palethorpe, Giuseppe Ercoli, Elisa Ramos-Sevillano, Gathoni Kamuyu, Joe Campo, Samuel Willcocks, Rie Nakajima, Philip Felgner, Brendan Wren, Ganjana Lertmemongkolchai, Richard Stabler, Jeremy Brown

The World Health Organisation has identified Acinetobacter baumannii as a critical priority antimicrobial resistant (AMR) pathogen for which new therapeutics are needed. Despite this, currently there are no antibody or vaccine candidates in advanced clinical development for A. baumannii. To help address this, we designed a protein microarray approach to identify multiple A. baumannii protein antigens for further investigation as potential targets for vaccination or an antibody therapy. An 868-protein microarray was constructed containing mainly highly conserved A. baumannii proteins, and was enriched for those predicted to be surface localised and for which the corresponding gene is highly expressed during culture in ex vivo human serum. Probing the protein microarray with sera obtained from mice after non-lethal infection with multiple different A. baumannii strains identified IgG responses to 66 proteins. Four proteins (three previously poorly described outer membrane proteins and BamA, a known protective vaccine antigen selected as a positive control) were selected for further investigation. Polyclonal rabbit IgG to all four protein antigens recognised multiple clinical AMR A. baumannii strains, and for selected strains promoted opsonisation with IgG and complement, improved neutrophil phagocytosis, and increased membrane attack complex formation. Passive immunisation with polyclonal IgG to each antigen partially protected mice against A. baumannii sepsis, and a combination of polyclonal to two antigens completely protected against A. baumannii murine sepsis. Repeating passive immunisation experiments in mice depleted of complement, neutrophils or tissue macrophages demonstrated protection against systemic infection was dependent on complement and neutrophils but not macrophages. Overall, the data demonstrate that our protein microarray is a novel approach that can rapidly identify multiple new protein antigens as potential antibody targets for preventing or treating AMR bacterial infections.

MYSM1-mediated epigenetic modification dysregulation leads to immunosuppression and secondary infections in sepsis

2026-02-12T14:00:00Z

by Jiali Xiong, Xin Cheng, Xiaoxing Xiong, Heyang Zhang, Qi An, Zhiqiang Li, Hong Fan, Guangli Li, Wei Li, Mingfu Tian, Jingjun Lv

Sepsis is a life-threatening condition characterized by a dysregulated immune response to infection, often leading to organ dysfunction and even death. During the recovery phase of sepsis, patients frequently exhibit impaired antimicrobial function of immune cells, which exacerbates the state of immunosuppression and increases the risk of secondary infections. However, therapeutic strategies targeting sepsis-induced immunosuppression have yet to achieve breakthrough progress, with the core challenge lying in the significant gaps in understanding the molecular mechanisms underlying immunosuppression. In this study, we integrated clinical samples, mouse models, and molecular mechanisms to reveal that the reduction in macrophage function and epigenetic dysregulation, particularly histone ubiquitination, are central drivers of sepsis-induced immunosuppression. Further investigation demonstrated that MYSM1, a deubiquitinase, plays a pivotal role in regulating this ubiquitination process. Targeted deletion of the N-terminal domain of MYSM1 markedly enhances the inflammatory response during the early phase of secondary infection in sepsis, facilitating bacterial clearance and significantly mitigating tissue damage in the late phase of secondary infection, thereby improving the survival outcomes in mice. Overall, our study elucidates the role of MYSM1-mediated dysregulation of epigenetic modifications in the immune response during the late phase of sepsis, providing a novel therapeutic approach for addressing sepsis-related immune dysfunction.

Structural and mechanistic insights into caseinolytic protease inhibition for antimicrobial development against Pseudomonas plecoglossicida

2026-02-12T14:00:00Z

by Jingjie Chen, Ping Zhang, Hongxin Guan, Bing Gong, Xiaoding Li, Zekai Li, Fan Li, Biao Zhou, Xuemin Chen, Xinhua Chen, Songying Ouyang, Yong-An Zhang

The caseinolytic protease (ClpP) is an emerging antibacterial target. Pseudomonas plecoglossicida (Pp), a pathogen causing visceral white spot disease in Larimichthys crocea, encodes two ClpP paralogs, PpClpP1 and PpClpP2. This study characterizes their distinct structural and functional properties. Phylogenetic and biochemical analysis revealed that PpClpP2 functions as a canonical serine protease with high peptidase activity, while PpClpP1 is evolutionarily divergent, exhibiting low inherent activity due to an unconventional Ser-His-Pro catalytic triad and a truncated N-terminal domain. Cryo-EM structure determination of PpClpP1 confirmed a homotetradecameric assembly with a dilated axial pore and a non-canonical catalytic geometry. In contrast, AlphaFold-predicted PpClpP2 displayed a compact structure with a canonical Ser-His-Asp triad. The subunits formed a stable heterotetradecamer (PpClpP1P2) with enhanced proteolytic activity compared to individual homotetradecameric. Pull-down assays demonstrated that PpClpP2, but not PpClpP1, specifically interacts with the unfoldase PpClpX, and the PpClpP1P2 heterotetradecamer further augmented PpClpX-mediated degradation of model substrates. Notably, the proteasome inhibitor bortezomib (BTZ) selectively inhibited PpClpP1 by binding to a unique pocket near the active site without engaging the catalytic serine, thereby suppressing bacterial growth in a PpClpP1-dependent manner. This study elucidates the structural basis of functional divergence between PpClpP paralogs, highlights their synergistic interplay in proteolysis, and identifies PpClpP1 as a druggable target for antibacterial development.

Consequences of prion strain mixtures: Indifference, competition, or collusion

2026-02-11T14:00:00Z

by Amanda L. Woerman, Jason C. Bartz

Interferon-β induction heterogeneity during KSHV infection is correlated to levels and activation of the transcription factors ATF2 and RelA, and not IRF3

2026-02-11T14:00:00Z

by Machika Kaku, Marta Maria Gaglia

Careful regulation of type I interferons (IFN) like IFN-β is vital for balancing tissue damage and protection against infections. Heterogeneity in type I IFN expression among virally infected cells is a common phenomenon that may help limit IFN responses, but the source of this heterogeneity is poorly understood. We previously found that during Kaposi’s sarcoma-associated herpesvirus replication, type I IFN induction was limited to a small percentage of infected cells. This heterogeneity was not explained by viral gene expression. Here, we used a fluorescent reporter and fluorescence activated cell sorting to investigate the source of the heterogeneity. Surprisingly, the canonical IFN induction pathway culminating in the activation of the IRF3 transcription factor was similarly activated between cells that made high vs. low/no IFN-β. In contrast, the activation or expression of the two other IFN transcription factors, the NF-κB subunit RelA and the AP-1 subunit ATF2, correlated with IFN-β induction. Our results suggest that during viral infection, activation of IRF3 does not automatically result in IFN responses at the level of individual cells, but that other factors, such as NF-κB and AP-1, are limiting for type I IFN induction.

A humanized IFN-γ mouse model reveals skin eschar formation, enhanced susceptibility and scrub typhus pathogenesis

2026-02-11T14:00:00Z

by Ryan H. Cho, Lihai Gao, Hui Wang, Yixuan Zhou, Casey Gonzales, Dario Villacreses, Emmett A. Dews, Xiaofei Zhou, Ruili Lv, Hema P. Narra, Lynn Soong, Yuejin Liang

Scrub typhus, caused by Orientia tsutsugamushi (Ot) bacteria, is a serious acute febrile illness associated with significant mortality. No effective vaccine is currently available, largely due to the complex Ot strain diversity and an incomplete understanding of protective immune mechanisms. To overcome these challenges, there is a critical need for a suitable animal model that mimics human disease through the natural route of infection. Here, we report for the first time that a genetically engineered humanized mouse strain (with triple knockout/knock-in of IFN-γ and its receptors, abbreviated as hIFNG/hIFNGR), exhibits increased susceptibility to intradermal Ot infection compared to wild-type (WT) mice. This is evidenced by greater body weight loss, elevated bacterial burden, and reduced expression of interferon-stimulated genes (ISGs). hIFNG/hIFNGR mice exhibit pronounced biochemical abnormalities and tissue pathology accompanied by dysregulated T cell and neutrophil responses following infection. Notably, this novel mouse strain with human IFN-γ signaling can develop skin eschar-like lesions resembling those observed in human patients. Overall, our study introduces a promising mouse model to dissect the immunopathogenesis of scrub typhus and evaluate future vaccine candidates.

Correction: Identification of the Pseudomonas aeruginosa AgtR-CspC-RsaL pathway that controls Las quorum sensing in response to metabolic perturbation and Staphylococcus aureus

2026-02-10T14:00:00Z

by The PLOS Pathogens Staff

Precision targeting: The dawn of artificially customized disease resistance

2026-02-10T14:00:00Z

by Xinyue Fan, Shanwu Lyu, Wenqian Fan, Jie Shu, Xiaofei Cheng

Advanced plant disease management strategies are essential to sustainable agriculture and global food security. Advances in plant immunity have given rise to a variety of innovative disease control strategies, such as NLR gene transfer, RNA silencing technology, and CRISPR/Cas9-based gene disruption, as well as the use of immunity inducers. Recently, several novel resistance strategies, including the bioengineering of immunoreceptors, protease-triggered resistance design, and the sentinel approach, have enabled the customized development of disease resistance traits. These new approaches envisage a new paradigm of precision-targeted, artificially engineered resistance to enhance crop protection.

Amikacin-eravacycline combination mediates the synergistic elimination of carbapenem-resistant pathogens via in vitro and in vivo metabolic reprogramming

2026-02-10T14:00:00Z

by Xiaoli Yang, Yili Chen, Jinmei Yang, Jiaying Lei, Tinghua Liu, Yougang Mai, Xikang Tang

Carbapenem-resistant (CR) organisms (CRO) have been identified as critical priority pathogens, emphasizing the urgent need for novel therapeutic strategies. Combination therapy emerges as a promising approach to address multidrug-resistant bacterial infections. Here we demonstrate that eravacycline (ERV), in combination with amikacin (AMK), effectively eliminates a panel of clinically isolated CR Escherichia coli, CR Klebsiella pneumoniae, and CR Acinetobacter baumannii. Mechanistically, the AMK-ERV combination enhances bacterial oxidative phosphorylation, leading to an accumulation of reactive oxygen species, which induce oxidative stress and accelerate bacterial cell death. Notably, this combination significantly improves survival rates in mouse models of intra-abdominal infection, demonstrating efficacy against infections induced by CR pathogens. Furthermore, serum metabolomics reveals that the AMK-ERV combination upregulates metabolic pathways of lipids and amino acids. Interestingly, the amino acid methionine significantly enhances the antibacterial activity of ERV against CR pathogens both in vitro and in vivo. Our findings underscore the potential of repurposing AMK in combination with ERV to combat CR pathogens and propose a novel strategy for controlling these infections through the combination of antibiotics with specific metabolites such as methionine.

Quantitative proteomics of infected macrophages reveals novel Leishmania virulence factors

2026-02-10T14:00:00Z

by Nicolas Hagedorn, Albert Fradera-Sola, Melina Mitnacht, Tobias Gold, Ulrike Schleicher, Falk Butter, Christian J. Janzen

Leishmaniasis is a major public health problem, causing diseases ranging from self-healing skin lesions to life-threatening chronic infections. Understanding how Leishmania parasites evade the host defense system is crucial for understanding the different manifestations of the disease and for improving diagnostic tools and drug development. We performed high-resolution proteome profiling of Leishmania spp. across three species during macrophage infection and identified distinct temporal expression patterns. Clustering analysis revealed unique protein expression profiles for each Leishmania species, whereas pairwise enrichment analysis revealed specific up- and downregulation patterns at different infection stages. Our results confirmed known virulence factors and highlighted new ones, demonstrating how our dataset could be used. We validated the dataset by showing that deletion of putative L. mexicana virulence factors resulted in reduced stage differentiation capacity and infectivity.

A SARS-CoV-2 variant-induced NTD-targeting antibody enhances viral infection via a distinctive binding mode

2026-02-10T14:00:00Z

by Wenting Li, Congcong Liu, Yaning Li, Qi Gui, Lin Cheng, Qing Fan, Bing Zhou, Haiyan Wang, Xiangyang Ge, Zheng Zhang, Renhong Yan, Bin Ju

SARS-CoV-2 infection elicits both neutralizing and non-neutralizing monoclonal antibodies (mAbs), primarily targeting to the N-terminal domain (NTD), receptor-binding domain (RBD), and S2 subunit of the spike protein. Notably, a unique subset of NTD-targeting mAbs isolated from prototype Wuhan-Hu-1 strain infected donors displayed a capacity of facilitating the viral infection independent of the fragment crystallizable (Fc) region in vitro. However, the rapid evolution of SARS-CoV-2 variants, particularly with NTD mutations, has led to widespread immune evasion. Whether SARS-CoV-2 variants could still induce NTD-targeting infection-enhancing antibodies (NIEAs) remains unclear. Here, we identified a distinctive NIEA, ConD-854, from a Delta variant primarily infected donor, with broad infection-enhancing activities against most pre-Omicron variants but not against post-Omicron variants. Structural and functional analysis revealed that ConD-854 enhanced the viral infection through an Fc-independent bivalent binding mechanism with a largely shared recognition epitope, but its heavy-light chain orientation was nearly perpendicular relative to the reported prototype strain-induced NIEAs. Collectively, our findings demonstrated that the primary infection of Delta variant could still induce the NIEAs targeting the similar epitope as those elicited by prototype strain infection. Mutations in Delta NTD were located outside the infection-enhancing epitope and did not affect the induction of NIEAs. Remarkably, we defined a distinctive structural paradigm for an NIEA to recognize the viral epitope. These results enriched our understanding of antiviral antibodies and provided insights for future vaccine design.

Regnase-1-mediated regulation of neutrophils modulates SARS-CoV-2 pneumonia

2026-02-09T14:00:00Z

by Keiko Yasuda, Junichi Aoki, Kotaro Tanaka, Shintaro Shichinohe, Chikako Ono, Alexis Vandenbon, Daiya Ohara, Yukiko Muramoto, Songling Li, Daisuke Motooka, Hitomi Watanabe, Keiji Hirota, Gen Kondoh, Takeshi Noda, Daron M. Standley, Yuzuru Ikehara, Seiji Okada, Tokiko Watanabe, Yoshiharu Matsuura, Osamu Takeuchi

The innate immune response to viral infection needs to be tightly regulated to ensure effective pathogen clearance while avoiding excessive immune activation. During SARS-CoV-2 infection, however, the immune system often fails to elicit appropriate responses, resulting in cytokine-release syndrome in patients with COVID-19. In this study, we show that reduced expression of Regnase-1, an RNase that negatively regulates immune cell activation, confers resistance to infection with the mouse-adapted SARS-CoV-2 MA10 strain. In Regnase-1+^/– mice, altered neutrophil function contributed to the amelioration of MA10-induced pneumonia. Single-cell RNA sequencing of lung tissue during MA10 infection revealed four distinct neutrophil subsets, and among these, a subset characterized by an interferon-stimulated gene (ISG) signature was decreased in Regnase-1+^/– mice. Furthermore, Regnase-1+^/– neutrophils exhibited reduced ISG expression without corresponding changes in proinflammatory gene expression. Regnase-1 was found to repress the expression of Tsc22d3, a gene involved in the negative regulation of interferon responses, through its 3′ untranslated region. Collectively, these findings suggest that Regnase-1 attenuates resistance to SARS-CoV-2 MA10 infection by promoting excessive interferon responses in neutrophils.

Flexibility and modulation of translation initiation in enterovirus genomes

2026-02-09T14:00:00Z

by Rhian L. O'Connor, Georgia M. Cook, Jacqueline Hankinson, Ksenia Fominykh, Samantha H. Cheng, Daniel A. Nash, Aurélie Cenier, Komal M. Nayak, Stephen C. Graham, Janet E. Deane, Matthias Zilbauer, Andrew E. Firth, Valeria Lulla

Enteroviruses comprise a large group of mammalian pathogens that often utilize two open reading frames (ORFs) to encode their proteins: the upstream protein (UP) and the main polyprotein. In some enteroviruses, in addition to the canonical upstream AUG (uAUG), there is another AUG that may represent an alternative upstream initiation site. An analysis of enterovirus sequences containing additional upstream AUGs identified several clusters, including strains of pathogenic Enterovirus alphacoxsackie and E. coxsackiepol. Using ribosome profiling on coxsackievirus CVA13 (E. coxsackiepol), we demonstrate that both upstream AUG codons can be used for translation initiation in infected cells. Moreover, we confirm translation from both upstream AUGs using a reporter system. Mutating the additional upstream AUG in the context of CVA13 did not result in phenotypic changes in immortalized cell lines. However, the wild-type virus outcompeted this mutant in human intestinal organoids and differentiated neuronal systems, representing an advantage in physiologically relevant infection sites. Mutation of the stop codon of the shorter upstream ORF led to dysregulated translation of the other ORFs in the reporter system, suggesting a potential role for the additional uORF in modulating the expression level of the other ORFs. Additionally, we demonstrate regulation of uORF translation in response to stress. These findings reveal the remarkable plasticity of enterovirus IRES-mediated initiation and the competitive advantage of double-upstream-AUG-containing viruses in terminally differentiated intestinal organoids and neuronal systems.

Legionella effector protein SidG disrupts host cytoskeleton via targeting Arp2/3 complex

2026-02-09T14:00:00Z

by Jiayang Liu, Siyao Liu, Rundong Shu, Kelong Ma, Qian Lu, Jinli Ge, Hongtao Liu, Jiaqi Fu, Jiazhang Qiu

Legionella pneumophila is a facultative intracellular bacterial pathogen capable of surviving and replicating within host cells, including macrophages and protozoans. It employs the Dot/Icm type IV secretion system (T4SS) to inject over 330 effector proteins into host cells, manipulating various cellular processes to facilitate infection. Characterizing the functions of these effectors is crucial to deciphering the pathogenesis of L. pneumophila. In this study, we identified SidG as an effector containing a Cys-His-Asp triad, whose functional state is strictly gated by its interaction with the cellular GTPase Rac1, particularly via its C-terminal domain. Rac1-activated SidG then utilizes an acidic (A) domain to target the Arp2/3 complex, the key regulator of actin nucleation. Importantly, SidG disrupts cytoskeletal architecture via both Rac1- and Arp2/3-dependent mechanisms. During L. pneumophila infection, SidG is crucial to promote efficient bacterial invasion of host cells in a Cys-His-Asp motif-dependent manner. Together, our study elucidates a sophisticated pathogenic mechanism where a bacterial effector co-opts a host GTPase to allosterically regulate its function towards the Arp2/3 complex, thereby facilitating bacterial entry into host cells.

Cytotoxic lymphocytes counteract viral type I interferon immune evasion

2026-02-09T14:00:00Z

by Michael Y. Schakelaar, Liling Shan, Shuang Li, Rianne G. Bouma, Josefien W. Hommes, Jorine G. F. Sanders, Jan Meeldijk, Laura L. Winkler, Toine ten Broeke, Robert F. Kalejta, Niels Bovenschen

Viruses are recognized by host cell innate immunity through viral RNA/DNA sensing by cyclic GMP-AMP synthase (cGAS) stimulator of interferon genes (STING). However, many viruses evade cGAS-STING signaling and antiviral IFN-β response. Here, we show that natural killer (NK) cells counteract immune evasion of type I interferon response upon human cytomegalovirus (HCMV) infection. NK cells enhance IFN-β response in virus-infected cells more efficiently than perforin-knockout and GrM-knockout NK cells. Mechanistically, GrM cleaves viral pp71 into two fragments, the first, like full-length pp71, still inhibits cGAS-STING-IFN-β response but is rapidly degraded by the proteasome, and the second fragment that rather augments IFN-β and outperforms full-length pp71 inhibition of STING. NK cells cannot enhance IFN-β response in cells infected with HCMV that harbors a pp71 with a mutated GrM cleavage site. We conclude that NK cells use GrM to counteract cytomegaloviral innate immune evasion through pp71-mediated inhibition of cGAS-STING-IFN-β innate immune response.

Breaking disulfide bonds in a weakly bactericidal α-defensin unleashes a potent antimicrobial peptide with an altered conformation

2026-02-09T14:00:00Z

by Gan Luo, Mingzhu Zhao, Qingxia Wang, Yang Zhou, Dan Yao, Jue Zhang, Gang Wang, Junjie Zhang, Chongbing Liao, Wuyuan Lu

Harnessing antimicrobial peptides as bactericidal agents affords an attractive approach to developing new anti-infective therapies. We found that abolishing disulfide bonding in mouse cryptdin 1 (Crp1), a weakly bactericidal α-defensin of 35 residues, turned it into a potent antimicrobial peptide against Gram-negative bacteria. Here we report that Crp1 in its natively folded β-sheet structure forms high-ordered nanonets to cloak, but not kill, Escherichia coli, whereas its disulfide-devoid linear counterpart (L-Crp1) readily disintegrates the bacterial membrane as monomers. L-Crp1 adopts a helix-loop-helix conformation in molecular dynamics simulations, likely conducive to productive peptide-membrane interactions detrimental to bacteria. A truncated peptide spanning the helix-loop-helix, L-Crp1^1-25, maintains the same conformation as and similar membranolytic and bactericidal activities to L-Crp1. Remarkably, intraperitoneally administered L-Crp1^1-25 rescues E. coli-challenged mice from lethality in a sepsis model by effectively reducing bacterial burden, inflammation and tissue damage. Our studies cultivate additional mechanistic insights into the mode of action of defensins and shed new light on how to harness these host factors for potential therapeutic use.

Informed mutation of western equine encephalitis virus to heparan sulfate binding: Implications for rational design of alphavirus live attenuated vaccines

2026-02-09T14:00:00Z

by Tetyana Lukash, Shishir Poudyal, Theron C. Gilliland Jr., Thomas Klose, Chengqun Sun, Shauna N. Vasilatos, Jessica L. Farren, Long Kwan Metthew Lam, Richard J. Kuhn, William B. Klimstra

Encephalitogenic alphaviruses are mosquito-borne viruses that can cause fatal disease in humans and equines. Currently, there are no licensed vaccines or antiviral treatments for these infections. Western equine encephalitis virus (WEEV) is a member of this group that had not produced a human infection in over a decade. However, an outbreak of WEEV encephalitis in humans and equines was reported recently in South America, indicating a need for additional countermeasures. Blind passage approaches to generation of RNA virus live attenuated vaccines (LAVs) frequently result in acquisition of positively charged amino acid mutations that confer heparan sulfate (HS) binding and that are attenuating factors in resultant LAVs. To develop an informed approach for creation of alphavirus LAVs, we have utilized the WEEV McMillan (McM) strain as an HS weak/non-binding platform into which we have placed positively charged amino acid substitution mutations at positions in the E2 glycoprotein previously shown to confer HS-dependent infection upon other alphaviruses. This approach yielded four mutants with high efficiency HS binding and avirulence in mice, which were further subjected to yield optimization by in vitro selection of second-site mutations. Interestingly, the original mutations concomitantly increased HS interactions and reduced infection promoted by VLDLR and PCDH10 protein receptors, while the second site mutations improved infectivity mediated by VLDLR. Further, we report a newly generated 4.1Å cryo-EM reconstruction of WEEV McM strain into which we have mapped the mutations to provide an E2 glycoprotein domain-based representation of receptor binding site location.

Neural cells are susceptible to historic and recently emerged Oropouche virus strains

2026-02-09T14:00:00Z

by Kaleigh A. Connors, Maris R. Pedlow, Zachary D. Frey, Marjorie Cornejo Pontelli, Sean P. J. Whelan, W. Paul Duprex, Leonardo D’Aiuto, Zachary P. Wills, Amy L. Hartman

Oropouche fever is a re-emerging global viral threat caused by infection with Oropouche virus (OROV). While disease is generally self-limiting, historical and recent reports of neurologic involvement highlight the importance of understanding the neuropathogenesis of OROV. In this study, we characterize viral replication kinetics in neurons, microglia, and astrocytes derived from immortalized, primary, and induced pluripotent stem cell-derived cells, which are all permissive to infection with the prototypic OROV BeAn19991. We demonstrate cell-type dependent replication kinetics with both historic and recently emerged viral strains. Further, we show that ex vivo rat brain slice cultures can be infected by all OROV strains and produce antiviral cytokines and chemokines, which introduces an additional model to study OROV kinetics and tropism in the central nervous system. These findings provide insight into OROV neuropathogenesis and an initial assessment of newly emerged strains.

Correction: Correction: STAT3, MYC, and EBNA1 cooperate through a ZC3H18 transcriptional network to regulate survival and proliferation of EBV-positive lymphomas

2026-02-09T14:00:00Z

by The PLOS Pathogens Staff

Plasmodium falciparum stomatin-like protein forms a putative complex with a metalloprotease in distinct mitochondrial loci

2026-02-09T14:00:00Z

by Julie M.J. Verhoef, Ezra T. Bekkering, Cas Boshoven, Megan Hannon, Felix Evers, Nicholas I. Proellochs, Cornelia G. Spruijt, Taco W. A. Kooij

Members of the Stomatin, Prohibitin, Flotillin and HflK/C (SPFH) protein family form large membrane anchored or spanning complexes and are involved in various functions in different organelles. The human malaria causing parasite Plasmodium falciparum harbors four SPFH proteins, including prohibitin 1 and 2, prohibitin-like protein (PHBL), and stomatin-like protein (STOML), which all localize to the parasite mitochondrion. In the murine model parasite Plasmodium berghei, STOML appears essential for asexual blood-stage (ABS) development and is localized to puncta on mitochondrial branching points in oocyst stages. In this study, we show that deletion of STOML causes a significant growth defect and slower ABS development, while sexual-stage development remains unaffected. Parasites lacking STOML were not more sensitive to respiratory chain targeting drugs, rendering a function of STOML in respiratory chain assembly unlikely. Epitope tagging of endogenous STOML revealed a distinct punctate localization on branching points and endings of the ABS mitochondrial network. STOML resides in a large protein complex and pulldown experiments identified a zinc dependent metalloprotease, FtsH, as a likely interaction partner. The predicted AlphaFold2 structure of STOML shows high similarity with the bacterial HflK/C, which has been shown to form a large vault-like structure around bacterial FtsH hexamers. Combined, our results suggest that a similar STOML-FtsH complex localized to specific loci of P. falciparum mitochondria facilitate the parasite’s ABS development.

Mitochondrial ribosomes in apicomplexan and trypanosomatid parasites: Dissimilar drivers of complexity and convergent features

2026-02-09T14:00:00Z

by Ondřej Gahura, Prashant Chauhan

Exosome-mediated delivery of microRNAs by root-knot nematodes

2026-02-09T14:00:00Z

by M. Willow H. Maxwell, Alex Papp, Bharat Rohilla, Caitlin Simpson, Martin Fuller, Suruchi Roychoudhry, Chris A. Bell

Plant-parasitic nematodes secrete molecules to manipulate their hosts, but little is known about their mode of delivery and packaging. Here, we describe microRNA-containing exosomes that are secreted by root-knot nematodes and systemically increase host susceptibility. By revealing a novel mode of nematode-plant communication, our findings outline a mechanism for the delivery of nematode patho-molecules, offering a new target for disrupting parasitism at the level of vesicle-mediated delivery.

Mechanistic insights into CAM-induced disruption of HBV capsids revealed by all-atom MD simulations

2026-02-09T14:00:00Z

by Carolina Pérez-Segura, Boon Chong Goh, Jodi A. Hadden-Perilla

Capsid assembly modulators (CAMs) represent a promising antiviral strategy against hepatitis B virus (HBV), but their effects on pre-formed capsids remain incompletely understood. Here, all-atom molecular dynamics (MD) simulations of intact HBV capsids complexed with prototypical CAM-As (HAP1, HAP18) and CAM-Es (AT130), reveal how structural changes induced by small molecule binding in the interdimer interfaces propagate through the shell lattice to yield global morphological consequences. Each quasi-equivalent interface exhibits a unique response: A sites, located within the pentameric capsomers, are unfilled in these systems and altered marginally by the presence of CAMs in neighboring interfaces. B sites are the most open and “CAM-ready,” suggesting uptake requires minimal conformational perturbation on the local or global level. C sites emerge as hubs of allosteric control and the key drug target, as their occupancy creates local distortion that is broadcast to adjacent sites, driving capsid faceting and – in the case of CAM-As – the destabilization that precedes dissociation in favor of aberrant assembly. D sites, unfilled in these systems, act as structural sinks, absorbing distortions from adjacent interfaces within the hexameric capsomers. The extent of C site adjustment and the nature of D site counterbalance varies with CAM chemotype, highlighting the divergent effects of CAM-As versus CAM-Es. The tensegrity relationship between the four quasi-equivalent interfaces couples them into a global network for strain redistribution that is functionally allosteric, with CAM binding sites displaying signs of both positive and negative cooperativity. These new insights into HBV capsid dynamics clarify how CAMs alter them on the microsecond timescale and suggest that targeting strain redistribution in mature core particles could be leveraged therapeutically.

Impaired host shutoff is a fitness cost associated with baloxavir marboxil resistance mutations in influenza A virus PA/PA-X nuclease domain

2026-02-09T14:00:00Z

by Jack R. Case, Denys A. Khaperskyy

The polymerase acidic (PA) protein is a subunit of the trimeric influenza A virus (IAV) RNA-dependent RNA polymerase and the target of the anti-influenza drug baloxavir marboxil (BXM). As with other direct-acting antivirals, treatment with BXM can lead to selection of viruses carrying resistance mutations. If these mutations have negligible fitness costs, resistant viruses can spread widely and render existing treatments obsolete. Multiple BXM resistance mutations in the nuclease domain of PA have been identified, with I38T and I38M amino acid substitutions occurring frequently. These mutations have minimal to no effects on viral polymerase activity, virus replication, or transmission. However, for reasons that are not well understood, viruses with BXM resistance substitutions have not been able to compete with parental wild-type strains. The IAV genome segment encoding PA also encodes the host shutoff nuclease PA-X, which shares the endonuclease domain with PA but has a unique C-terminal domain generated by ribosomal frameshifting during translation. Unlike their effects on PA activity, the effects of BXM or the I38T/M substitutions on PA-X function remain uncharacterized. In our work, for the first time, we directly examine the effects of baloxavir and the I38T/M substitutions on PA-X activity and show that baloxavir inhibits PA-X activity in a dose dependent manner. Most importantly, we also demonstrate that the I38T/M mutations significantly impair the host shutoff activity of PA-X proteins from different IAV strains of H1N1, H3N2, and H5N1 subtypes. Our work reveals that the deleterious effects of I38T/M on PA-X function may represent an important barrier to the spread of BXM-resistant viruses.

Differential roles of the type I and II secretion systems for the intracellular ABC141 Acinetobacter baumannii infection, which elicits an atypical hypoxia response in endothelial cells

2026-02-09T14:00:00Z

by Charline Debruyne, Landon Hodge, Karsten Hokamp, Anna S. Ershova, Carsten Kröger, Suzana P. Salcedo

Acinetobacter baumannii poses a substantial global health threat, causing severe multi-drug-resistant infections in hospitalized patients. Circulating clinical isolates present remarkable diversity, with a proportion capable of establishing a transient intracellular niche suitable for persistence, multiplication, and spread. Yet, it remains unknown which bacterial factors mediate the formation and maintenance of this niche, especially within non-phagocytic cells, nor what host responses are elicited. This work demonstrates that the invasive A. baumannii ABC141 strain does not secrete ammonia in endothelial cells as previously shown for other A. baumannii strains multiplying within macrophages but resides in an acidic vacuole devoid of active lysosomal degradative enzymes. This compartment mediates bacterial egress and infection of neighboring cells, promoting dissemination. Using a Dual-RNAseq approach, we mapped the host and bacterial gene expression during the replicative stage of the infection. An atypical hypoxia cell response was observed without significant induction of the HIF1 pathway, with no metabolic shift or disturbance of mitochondria. Surprisingly, ABC141 efficiently grew in hypoxic conditions in culture and within host cells. In addition, we found a bacterial signature reflective of an adaptation to a nutrient-deprived environment. Our work also highlights a differential role for ABC141 secretion systems, with the T1SS assisting intracellular multiplication and the T2SS required for host cell invasion, implicating for the first time the T2SS in the intracellular lifecycle of invasive ABC141 in endothelial cells.

B Cell Receptor’s function in virus entry: Anti-SARS-CoV-2 B cell receptors can mediate viral entry in an ACE2-independent mechanism

2026-02-06T14:00:00Z

by Rene Larios, Md Belal Hossain, Rebecca Brown, Arjit Vijey Jeyachandran, Angel Elma Abu, Anne Kathrin Zaiss, Christina M. Ramirez, Masakazu Kamata, Steve Cole, Ting-Ting Wu, Kenneth Dorshkind, Vaithilingaraja Arumugaswami, Kouki Morizono

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.

PLOS Pathogens

It’s not me, it’s you: Anti-phage nuclease specificity inside a bacterium

Csep1P protein from Campylobacter concisus induces a chemokine-dominant inflammatory state in macrophages and enhances proinflammatory response to gut bacteria

A type III secretion system is required for Bordetella atropi invasion of host cells in vivo

The UBC/SIRT5/DRP1 axis regulates mitochondrial dynamics to alleviate Staphylococcus aureus-induced oxidative stress and senescence in bovine mammary epithelial cells

Identification of multiple Acinetobacter baumannii protein antigens as targets for potential immunotherapies using a novel protein microarray screening approach

MYSM1-mediated epigenetic modification dysregulation leads to immunosuppression and secondary infections in sepsis

Structural and mechanistic insights into caseinolytic protease inhibition for antimicrobial development against Pseudomonas plecoglossicida

Consequences of prion strain mixtures: Indifference, competition, or collusion

Interferon-β induction heterogeneity during KSHV infection is correlated to levels and activation of the transcription factors ATF2 and RelA, and not IRF3

A humanized IFN-γ mouse model reveals skin eschar formation, enhanced susceptibility and scrub typhus pathogenesis

Correction: Identification of the Pseudomonas aeruginosa AgtR-CspC-RsaL pathway that controls Las quorum sensing in response to metabolic perturbation and Staphylococcus aureus

Precision targeting: The dawn of artificially customized disease resistance

Amikacin-eravacycline combination mediates the synergistic elimination of carbapenem-resistant pathogens via in vitro and in vivo metabolic reprogramming

Quantitative proteomics of infected macrophages reveals novel Leishmania virulence factors

A SARS-CoV-2 variant-induced NTD-targeting antibody enhances viral infection via a distinctive binding mode

Regnase-1-mediated regulation of neutrophils modulates SARS-CoV-2 pneumonia

Flexibility and modulation of translation initiation in enterovirus genomes

Legionella effector protein SidG disrupts host cytoskeleton via targeting Arp2/3 complex

Cytotoxic lymphocytes counteract viral type I interferon immune evasion

Breaking disulfide bonds in a weakly bactericidal α-defensin unleashes a potent antimicrobial peptide with an altered conformation

Informed mutation of western equine encephalitis virus to heparan sulfate binding: Implications for rational design of alphavirus live attenuated vaccines

Neural cells are susceptible to historic and recently emerged Oropouche virus strains

Correction: Correction: STAT3, MYC, and EBNA1 cooperate through a ZC3H18 transcriptional network to regulate survival and proliferation of EBV-positive lymphomas

Plasmodium falciparum stomatin-like protein forms a putative complex with a metalloprotease in distinct mitochondrial loci

Mitochondrial ribosomes in apicomplexan and trypanosomatid parasites: Dissimilar drivers of complexity and convergent features

Exosome-mediated delivery of microRNAs by root-knot nematodes

Mechanistic insights into CAM-induced disruption of HBV capsids revealed by all-atom MD simulations

Impaired host shutoff is a fitness cost associated with baloxavir marboxil resistance mutations in influenza A virus PA/PA-X nuclease domain

Differential roles of the type I and II secretion systems for the intracellular ABC141 Acinetobacter baumannii infection, which elicits an atypical hypoxia response in endothelial cells

B Cell Receptor’s function in virus entry: Anti-SARS-CoV-2 B cell receptors can mediate viral entry in an ACE2-independent mechanism

Csep1^P protein from Campylobacter concisus induces a chemokine-dominant inflammatory state in macrophages and enhances proinflammatory response to gut bacteria