Streptococcus suis (S. suis) is an important zoonotic pathogen that causes severe infections in humans and animals worldwide. Upon infection, the host innate immune system produces host defense peptides (HDPs) to resist S. suis invasion. PMAP-36, a porcine-derived HDP, has been shown to fail to kill S. suis, suggesting that this pathogen has evolved strategies to evade PMAP-36-mediated immune defense. However, the exact mechanism by which S. suis responds to PMAP-36 remains unclear. Here we showed that PMAP-36 significantly enhanced S. suis adhesion, cytotoxicity, and virulence gene expression. The two-component system (TCS) VraSR was essential for PMAP-36 to promote S. suis pathogenicity. We demonstrated that PMAP-36 directly bound to the sensor kinase VraS. Further transcriptomic analysis revealed that VraSR sensed PMAP-36 to regulate fatty acid biosynthesis, in which a key gene accD expression was significantly downregulated in both PMAP-36-treated ΔvraS and ΔvraR mutant strains. Deletion of accD attenuates S. suis in vivo pathogenicity, including reduced bacterial loads, alleviated organ damage, and decreased inflammatory response. Additionally, VraSR-mediated accD expression was critical for S. suis-induced cytotoxicity and inflammatory response, as deletion of vraS or vraR fails to reduce inflammatory cytokines production due to sustained high accD expression. This study reveals VraSR-mediated virulence regulatory mechanism in response to HDP activation, which provides new insight into the development of novel strategies to combat S. suis infection.
Avian influenza viruses (AIVs) are recognized as persistent threats to poultry health and global food security. The H9N2 subtype is widely distributed in poultry. A nationwide epidemiological survey was conducted in South, North, Central, and Southwest China, including Muscovy duck farms and live poultry markets, from 2022 to 2024. A total of 1208 Muscovy duck serum samples, 1212 duck-derived oropharyngeal/cloacal swabs and lung/tracheal tissues, and 480 chicken-derived samples were collected. In addition, 31 H9N2 strains were isolated, 2 of which were duck derived and 29 of which were chicken derived. A novel coinfection challenge model combining ocularnasal inoculation of H9N2 with injection of Escherichia coli (E. coli) was established, which induced severe tracheal lesions that closely resembled naturally occurring field pathologies. The coinfection challenge model successfully replicated prevalent field scenarios of viral‒bacterial synergism, resulting in severe lung lesions and a significant increase in viral loads. The results demonstrated that inactivated and live-vector vaccines provided more than 80
Streptococcus suis is a pathogenic bacterium primarily found in pigs, where it causes sudden death and meningitis, but it is also capable of causing septic shock and meningitis in humans, being the most important cause of adult bacterial meningitis in Southeast Asia. As the host’s innate immune system serves as the first line of defense against microbial invaders, it is crucial to understand the intricate relationship between the bacterium and this system. Despite an increasing number of studies performed in the last 20 years, the pathogenesis of S. suis infection is not fully understood, and there is still an absence of effective vaccines on the market. Recent population-genomic studies have further highlighted that pathogenic S. suis is not a single uniform entity but comprises multiple lineages with distinct genome content and disease associations, raising the possibility that innate immune evasion mechanisms may not be equivalent across lineage. In the current article, we conducted a comprehensive review of the literature, focusing on the innate response developed mainly by phagocytes against this Gram-positive bacterium. Our aim was to summarize the last findings and to identify the main gaps in knowledge to guide future research efforts toward areas that require further investigation.
Porcine reproductive and respiratory syndrome (PRRS), caused by the PRRS virus (PRRSV), remains one of the most economically significant infectious diseases affecting the global swine industry, resulting in annual losses exceeding US 1.2 billion in the USA alone. PRRSV infects porcine alveolar macrophages (PAMs) and induces profound mitochondrial dysfunction, leading to the release of mitochondrial DNA (mtDNA). However, the mechanisms by which PRRSV-induced mitochondrial damage acts as a damage-associated molecular pattern (DAMP) to trigger inflammatory responses have not been fully elucidated. Here, we report that highly pathogenic PRRSV (HP-PRRSV) infection upregulates interleukin-1β (IL-1β) messenger RNA (mRNA) expression and protein secretion in a dose- and time-dependent manner. Transmission electron microscopy revealed progressive mitochondrial swelling, cristae disorganization, and matrix loss during HP-PRRSV infection. Using RNAscope combined with MitoGreen staining, we discovered that mitochondrial double-stranded RNA (mtdsRNA), generated from bidirectional transcription of mitochondrial DNA, is released into the cytosol during PRRSV infection. In vitro, transcription-driven mtdsRNA or mtdsRNA isolated from PAMs directly activated the NLRP3 inflammasome, inducing caspase-1 cleavage and IL-1β secretion. Mechanistically, the PRRSV-encoded nonstructural protein 11 (nsp11) inhibited NLRP3-dependent inflammatory responses by suppressing the oligomerization of the apoptosis-associated speck-like protein containing a caspase recruitment domain (CARD) (ASC), thereby constraining excessive inflammation and establishing a delicate balance between pro-inflammatory signaling and viral immune evasion. Collectively, our findings identify mtdsRNA as a previously unrecognized mitochondrial DAMP that links PRRSV-induced mitochondrial injury to NLRP3 inflammasome activation, while also revealing a counter-regulatory role for nsp11 in modulating inflammation.
Bovine coronavirus (BCoV), a primary etiological agent of calf diarrhea, exhibits dual tropism for the respiratory and enteric tracts. However, research on BCoV gene function and pathogenesis has been limited by the lack of convenient and flexible reverse genetics tools. Herein, we report a robust reverse genetics system for BCoV based on an optimized circular polymerase extension reaction (CPER) methodology. We successfully rescued recombinant BCoV (rBCoV) in HRT-18G cells and engineered recombinant BCoV expressing ZsGreen fluorescent protein (rBCoV/Zs-T2A-ns2). Phenotypic analysis demonstrated that both unmodified rBCoV and rBCoV/Zs-T2A-ns2 maintained growth kinetics comparable to the wild-type BCoV. Importantly, the reporter virus demonstrated remarkable genetic stability for over ten passages, identifying the ns2 locus as a suitable insertion site for stable foreign gene expression without compromising viral fitness or sequence integrity. As a proof-of-concept application, the rBCoV/Zs-T2A-ns2 was employed for antiviral compound evaluation, successfully identifying four compounds—camostat, nafamostat, niclosamide, and nelfinavir—capable of effectively inhibiting BCoV replication. Further time-of-addition assays revealed that nelfinavir and niclosamide targeted the BCoV replication stage, while camostat and nafamostat interfered with BCoV internalization. This versatile CPER-based reverse genetics system provides a critical platform for advanced BCoV pathogenesis research and accelerated development of novel vaccines and effective antiviral therapeutics, ultimately contributing to enhanced bovine health and sustainable livestock production.
