Role of feline ANP32 proteins in regulating polymerase activity of influenza A virus

Recently,increasing natural infection cases and experimental animal challenge studies demonstrated domestic cats are susceptible to multiple subtypes influenza A virus(IAV)infections.Notably,some subtype IAV strains could circulate in domestic cats after cross-species transmission and even infected humans,posing a threat to public health.Host factors related to viral polymerase activity could determine host range of IAV and acidic nuclear phosphoprotein 32(ANP32)is the most important one among them.However,role of cat-derived ANP32 on viral polymerase activity and host range of IAV is still unknown.In the present study,a total of 10 feline ANP32(feANP32)splice variants(including 5 feANP32A,3 feANP32B,and 2 feANP32E)were obtained from domestic cats by RT-PCR.Sequence alignment results demonstrated amino acid deletions and/or insertions occurred among feANP32 variants,but all feANP32 proteins were primarily localized to cell nucleus.Minigenome replication systems for several representative IAV strains were established and the support ability of feANP32 on IAV polymerase activity was estimated.The results indicated that most feANP32A and feANP32B splice variants were able to support all the tested IAV strains,though the support activity of a single feANP32 protein on polymerase activity varied among different IAV strains.In addition,the role of feANP32 in supporting H3N2 canine influenza virus was determined by investigating viral replication in vitro.Collectively,our study systematically investigated the support activity of feANP32 on IAV,providing a clue for further exploring the mechanism of susceptibility of cats to IAV.

Structural basis for dsRNA recognition by NS1 protein of influenza A virus

Influenza A viruses are important human pathogens causing periodic pandemic threats. Nonstructural protein 1 （NS1） protein of influenza A virus （NS1A） shields the virus against host defense. Here, we report the crystal structure of NS1A RNA-binding domain （RBD） bound to a double-stranded RNA （dsRNA） at 1.7A. NS1A RBD forms a homodimer to recognize the major groove of A-form dsRNA in a length-independent mode by its conserved concave surface formed by dimeric anti-parallel a-helices, dsRNA is anchored by a pair of invariable arginines （Arg38） from both monomers by extensive hydrogen bonds. In accordance with the structural observation, isothermal titration calorimetry assay shows that the unique Arg38-Arg38 pair and two Arg35-Arg46 pairs are crucial for dsRNA binding, and that Ser42 and Thr49 are also important for dsRNA binding. Agrobacterium co-infiltration assay further supports that the unique Arg38 pair plays important roles in dsRNA binding in vivo.

Molecular Characterization of Avian-like H1N1 Swine Influenza A Viruses Isolated in Eastern China, 2011

Currently, three predominant subtypes of influenza virus are prevalent in pig populations worldwide： H1N1, H3N2, and H1N2. European avian-Hke H1N1 viruses, which were initially detected in European pig populations in 1979, have been circulating in pigs in eastern China since 2007. In this study, six influenza A viruses were isolated from 60 swine lung samples collected from January to April 2011 in eastern China. Based on whole genome sequencing, molecular characteristics of two isolates were determined. Phylogenetic analysis showed the eight genes of the two isolates were closely related to those of the avian-like H1N1 viruses circulating in pig populations, especially similar to those found in China. Four potential glycosylation sites were observed at positions 13, 26, 198, 277 in the HA1 proteins of the two isolates. Due to the presence of a stop codon at codon 12, the isolates contained truncated PB1-F2 proteins. In this study, the isolates contained 591Q, 627E and 701N in the polymerase subunit PB2, which had been shown to be determinants of virulence and host adaptation. The isolates also had a D rather than E at position 92 of the NS1, a marker of mammalian adaptation. Both isolates contained the GPKV motif at the PDZ ligand domain of the 3＇ end of the NS1, a characteristic marker of the European avian-like swine viruses since about 1999, which is distinct from those of avian, human and classical swine viruses. The M2 proteins of the isolates have the mutation （S31N）, a characteristic marker of the European avian-like swine viruses since about 1987, which may confer resistance to amantadine and rimantadine antivirals. Our findings further emphasize the importance of surveillance on the genetic diversity of influenza A viruses in pigs, and raise more concerns about the occurrence of cross-species transmission events.

Genetic Analysis and Rescue of a Triple-reassortant H3N2 Influenza A Virus Isolated From Swine in Eastern China

One influenza H3N2 virus, A/swine/Shandong/3/2005 (Sw/SD/3/2005), was isolated from pigs with respiratory disease on a farm in eastern China. Genetic analysis revealed that Sw/SD/3/2005 was a triple-reassortant virus with a PB2 gene from human-like H1N1, NS from classical swine H1N1, and the remaining genes from human-like H3N2 virus. These findings further support the concept that swine can serve as reservoir or mixing vessels of influenza virus strains and maintain genetic and antigenic stability of viruses. Furthermore, we have successfully established a reverse genetics system based on eight plasmids and rescued Sw/SD/3/2005 through cell transfection. HI tests and RT-PCR confirmed that the rescued virus maintained the biological properties of the wild type Sw/SD/3/2005. The successful establishment of the reverse genetics system of Sw/SD/3/2005 will enable us to conduct extensive studies of the molecular evolution of H3N2 influenza viruses in swine.

Possible Impact of Global Warming on the Evolution of Hemagglutinins from Influenza A Viruses

Objective To determine if global warming has an impact on the evolution of hemagglutinins from influenza A viruses, because both global warming and influenza pandemics/epidemics threaten the world. Methods 4 706 hemagglutinins from influenza A viruses sampled from 1956 to 2009 were converted to a time‐series to show their evolutionary process and compared with the global, northern hemisphere and southern hemisphere temperatures, to determine if their trends run in similar or opposite directions. Point‐to‐point comparisons between temperature and quantified hemagglutinins were performed for all species and for the major prevailing species. Results The comparisons show that the trends for both hemagglutinin evolution and temperature change run in a similar direction. Conclusion Global warming has a consistent and progressive impact on the hemagglutinin evolution of influenza A viruses.

Generation and application of two monoclonal antibodies targeting conserved linear epitopes in the NP protein of influenza A virus

Monoclonal antibodies(mAbs) are widely used in virus research and disease diagnosis. The nucleoprotein(NP) of influenza A virus(IAV) plays important roles in multiple stages of the virus life cycle. Therefore, generating conserved mAbs against NP and characterizing their properties will provide useful tools for IAV research. In this study, two mAbs against the NP protein, 10 E9 and 3 F3, were generated with recombinant truncated NP proteins(NP-1 and NP-2) as immunogens. The heavy-chain subclass of both 10 E9 and 3 F3 was determined to be IgG2α, and the light-chain type was κ. Truncation and site-specific mutation analyses showed that the epitopes of mAbs 10 E9 and 3 F3 were located in the N terminal 84–89 amino acids and the C terminal 320–324 amino acids of the NP protein, respectively. We found that mAbs 10 E9 and 3 F3 reacted well with the NP protein of H1–H15 subtypes of IAV. Both 10 E9 and 3 F3 can be used in immunoprecipitation assay, and 10 E9 was also successfully applied in confocal microscopy. Furthermore, we found that the 10 E9-recognized _(84) SAGKDP_(89) epitope and 3 F3-recognized 320 ENPAH324 epitope were highly conserved in NP among all avian and human IAVs. Thus, the two mAbs we developed could be used as powerful tools in the development of diagnostic methods of IAV, and also surely promote the basic research in understanding the replication mechanisms of IAV.

Detection of the Pandemic H1N1/2009 Influenza A Virus by a Highly Sensitive Quantitative Real-time Reverse-transcription Polymerase Chain Reaction Assay

A quantitative real time reverse-transcription polymerase chain reaction （qRT-PCR） assay with specific primers recommended by the World Health Organization （WHO） has been widely used successfully for detection and monitoring of the pandemic H1N1/2009 influenza A virus. In this study, we report the design and characterization of a novel set of primers to be used in a qRT-PCR assay for detecting the pandemic H1N1/2009 virus. The newly designed primers target three regions that are highly conserved among the hemagglutinin （HA） genes of the pandemic HlN1/2009 viruses and are different from those targeted by the WHO-recommended primers. The qRT-PCR assays with the newly designed primers are highly specific, and as specific as the WHO-recommended primers for detecting pandemic H1N1/2009 viruses and other influenza viruses including influenza B viruses and influenza A viruses of human, swine, and raccoon dog origin. Furthermore, the qRT-PCR assays with the newly designed primers appeared to be at least 10-fold more sensitive than those with the WHO-recommended primers as the detection limits of the assays with our primers and the WHO-recommended primers were 2.5 and 25 copies of target RNA per reaction, respectively. When tested with 83 clinical samples, 32 were detected to be positive using the qRT-PCR assays with our designed primers, while only 25 were positive by the assays with the WHO-recommended primers. These results suggest that the qRT-PCR system with the newly designed primers represent a highly sensitive assay for diagnosis of the pandemic HIN1/2009 virus infection.

Nested RT-PCR method for the detection of European avian-like H1 swine influenza A virus

Swine influenza A virus（swine IAV） circulates worldwide in pigs and poses a serious public health threat, as evidenced by the 2009 H1N1 influenza pandemic. Among multiple subtypes/lineages of swine influenza A viruses, European avian-like（EA） H1N1 swine IAV has been dominant since 2005 in China and caused infections in humans in 2010. Highly sensitive and specific methods of detection are required to differentiate EA H1N1 swine IAVs from viruses belonging to other lineages and subtypes. In this study, a nested reverse transcription（RT）-PCR assay was developed to detect EA H1 swine IAVs. Two primer sets（outer and inner） were designed specifically to target the viral hemagglutinin genes. Specific PCR products were obtained from all tested EA H1N1 swine IAV isolates, but not from other lineages of H1 swine IAVs, other subtypes of swine IAVs, or other infectious swine viruses. The sensitivity of the nested RT-PCR was improved to 1 plaque forming unit（PFU） m L^（-1） which was over 10~4 PFU m L^（-1） for a previously established multiplex RT-PCR method. The nested RT-PCR results obtained from screening 365 clinical samples were consistent with those obtained using conventional virus isolation methods combined with sequencing. Thus, the nested RT-PCR assay reported herein is more sensitive and suitable for the diagnosis of clinical infections and surveillance of EA H1 swine IAVs in pigs and humans.

Novel H1N1 influenza A virus infection in a patient with acute rejection after liver transplantation

BACKGROUND:The 2009 H1N1 influenza A virus was first identified in April 2009 and rapidly evolved into a pandemic. Recipients of solid-organ transplants have a higher risk for severe infection because of immunosuppression.There are limited reports of 2009 H1N1 influenza in liver transplant recipients,especially in China. METHODS:We present a case of a 48-year-old male liver transplant recipient with 2009 H1N1 influenza A virus.He received therapy for acute rejection after transplantation and was confirmed with H1N1 virus infection. RESULTS:The patient was started on oseltamivir(75 mg, orally twice daily)and had a benign hospital course,with defervescence and resolution of symptoms within 72 hours. The follow-up chest radiograph after discharge was normal. CONCLUSIONS:The 2009 H1N1 influenza in this hospitalized transplant recipient was relatively mild,and prolonged viral shedding was not noted.Oseltamivir can be a valid measure in immunocompromised individuals.

In silico modification of oseltamivir as neuraminidase inhibitor of influenza A virus subtype H1N1

This research focused on the modification of the functional groups of oseltamivir as neuraminidase inhibitor against influenza A virus subtype H1N1.Interactions of three of the best ligands were evaluated in the hydrated state using molecular dynamics simulation at two different temperatures.The docking result showed that AD3BF2 D ligand（N-[（1S,6R）-5-amino-5-{[（2R,3S,4S）-3,4-dihydroxy-4-（hydroxymethyl） tetrahydrofuran-2-yl]oxy}-4-formylcyclohex-3-en-1-yl]acetamide-3-（1-ethylpropoxy）-1-cyclohexene-1-carboxylate） had better binding energy values than standard oseltamivir.AD3BF2 D had several interactions,including hydrogen bonds,with the residues in the catalytic site of neuraminidase as identified by molecular dynamics simulation.The results showed that AD3BF2 D ligand can be used as a good candidate for neuraminidase inhibitor to cope with influenza A virus subtype H1N1.

Enhancement of Virus Replication in An Influenza A Virus NS1-Expresssing 293 Cell Line

The nonstructural protein 1 （NS1） of influenza A virus, which is absent from the viral particle, but highly expressed in infected cells, strongly antagonizes the interferon （IFN）-mediated antiviral response. We engineered an NS1-expressing 293 （293-NS1） cell line with no response to IFN stimulation. Compared with the parental 293 cells,

Evaluation of A Single-reaction Method for Whole Genome Sequencing of Influenza A Virus using Next Generation Sequencing

Objective To evaluate a single-reaction genome amplification method, the multisegment reverse transcription-PCR （M-RTPCR）, for its sensitivity to full genome sequencing of influenza A virus, and the ability to differentiate mix-subtype virus, using the next generation sequencing （NGS） platform. Methods Virus genome copy was quantified and seria（iy diluted to different titers, followed by amplification with the M-RTPCR method and sequencing on the NGS platform. Furthermore, we manually mixed two subtype viruses to different titer rate and amplified the mixed virus with the M-RTPCR protocol, followed by whole genome sequencing on the NGS platform. We also used clinical samples to test the method performance. Results The M-RTPCR method obtained complete genome of testing virus at 125 copies/reaction and determined the virus subtype at titer of 25 copies/reaction. Moreover, the two subtypes in the mixed virus could be discriminated, even though these two virus copies differed by 200-fold using this amplification protocol. The sensitivity of this protocol we detected using virus RNA was also confirmed with clinical samples containing Iow-titer virus. Conclusion The M-RTPCR is a robust and sensitive amplification method for whole genome sequencing of influenza A virus using NGS platform.

Anti-Influenza A Virus Effect of Hypericum perforatum L. Extract

To study the antiviral effect of Hypericum perforatum L. extract （HPE） on influenza A virus （IAV） （H1N1） in vitro and in vivo. Cytopathic effect （CPE） and neutral red （NR） dye uptake were used to examine the antiviral effect of HPE on Madin Darby Canine Kidney （MDCK） cells which were infected with IAV in vitro HPE was effective against influenza A virus （IAV） in vitro, with a 50% effective concentration （EC50） of 40 ug/mL, The mean 50% cytotoxic concentration （CC50） in the MDCK used in these experiments was 1.5 mg/mL. Ribavirin was run in parallel with EC50 values of 5.0 ug/mL; the mean CC50 for ribavirin was 520 ug/mL. Oral gavage administrations of HPE or ribavirin to mice infected with the IAV were highly effective in preventing death, slowing the decline of arterial oxygen saturation, inhibiting lung consolidation and reducing lung virus titers. The minimum effective dose of HPE in these studies was 31.25 mg/kg/day, which was administered twice daily for 5 d beginning 4 h prior to virus exposure. Below a dosage of 2000 mg/kg/day, almost all treated mice survived, which suggests that HPE is of low toxicity. Ribavirin＇s minimum effective dose was 40 mg/kg/day with the LDso determined to be 200 mg/kg/day. Delay of the initiation of either HPE or ribavirin therapy, using approximately 1/3 LD50 dose each time, could still be protective as late as 48 h after exposure to the IAV. While both agents appeared to have similar efficacy against IAV infections, HPE was considered to be less toxic and may warrant further evaluation as a possible therapy for influenza.

Feedforward loop profile among transcription factor, miRNA and mRNA in influenza A virus-infected mouse lungs

Purpose:In the present study,we focused on the 46 microRNAs and 719 genes in the microRNA-gene network,reported by us,and aimed to build a research blueprint of feedforward loops and reveal the key TFs in H1N1-infected mouse lung.Method:Based on microRNAs and genes in the microRNA-gene network previously reported by us,we used Jemboss software to find relationships between TFs and microRNAs(or genes),and then built a TF-microRNA-gene network exploiting the interactions between TFs and microRNAs(or genes).Next,we searched the sequences of above genes or microRNAs near the transcription start site(TSS)area,and then used the MatchTM algorithm to predict relevant TFs,and built the TF-Gene-Network.Result:We built a TF-microRNAgene network and exploreed eight key TFs,namely NF-AT1,GKLF,SRY,SOX10,AML1,MZF1,CRX and myogenin,in the network,and then constructed subgraphs of these eight TFs.Simultaneously,we predicted the possible target genes of microRNAs and identified the feedforward regulation relationship of possible TFs,microRNAs and mRNAs.The results showed that all eight factors with a score greater than 100 were TFs,namely NF-AT1,GKLF,SRY,SOX10,AML1,CRX,myogenin and MZF1.We then constructed subtables of the above eight TFs.Conclusion:In this study,TFs including NF-AT1,GKLF,SRY,SOX10,AML1,MZF1,CRX and myogenin showed the highest score(>100)not only in the TF-microRNA-gene network but also in feedforward loops,indicating that these eight TFs play the most important roles in mouse H1N1 influenza virus infection biology.

Study on the mechanism of action of Ephedra Herba Decoction against influenza A virus based on network pharmacology

Objective To predict the main bioactive components and potential mechanisms of Ephedra Herba Decoction(Chinese Pinyin abbreviated as MHT)in treating influenza A virus(IAV)based on network pharmacology.Methods Multiple online databases were used to search and screen out the active components from MHT,the related targets of active components of MHT and the genes related to IAV.Search the corresponding genes name of target through UniProt database.Cytoscape 3.7.2 was used to construct the drug-component-target network diagram.Venn diagram was used to screen the intersection genes of the active components corresponding to the target and disease-related genes,and the intersection genes were imported into the STRING Database Online platform to obtain the protein-protein interaction(PPI)network.Then,the PPI network was imported into Cytoscape 3.7.2 to obtain the core targets.Finally,Wei Sheng Xing(http://www.bioinformatics.com.cn/)was used to do GO function enrichment analysis and KEGG signaling pathway enrichment analysis for the intersection genes,and the results of GO and KEGG were visualized.Results A total of 116 active components and 253 potential targets were screened from MHT.Quercetin,Kaempferol,and Luteolin are the main active components,and AKT1,TNF,TP53,IL6,and JUN are the core targets of 253 potential targets.There are 2906 targets of influenza A,including 121 intersection genes.Enrichment analysis showed that there were 131 entries of molecular function,89 entries of cell component,1645 entries of biological process and 195 entries of signaling pathway.PI3K-Akt,MAPK,and JAK-STAT were the main signaling pathways.Conclusion MHT plays an important role in the prevention and treatment of influenza A by acting on multiple targets and multiple signaling pathways.

M6PR interacts with the HA2 subunit of influenza A virus to facilitate the fusion of viral and endosomal membranes

Influenza A virus(IAV) commandeers numerous host cellular factors for successful replication. However, very few host factors have been revealed to be involved in the fusion of viral envelope and late endosomal membranes. In this study, we identified cation-dependent mannose-6-phosphate receptor(M6PR) as a crucial host factor for the replication of IAV. We found that siRNA knockdown of M6PR expression significantly reduced the growth titers of different subtypes of IAV, and that the inhibitory effect of M6PR siRNA treatment on IAV growth was overcome by the complement of exogenously expressed M6PR. When A549 cells were treated with siRNA targeting M6PR,the nuclear accumulation of viral nucleoprotein(NP) was dramatically inhibited at early timepoints post-infection, indicating that M6PR engages in the early stage of the IAV replication cycle. By investigating the role of M6PR in the individual entry and post-entry steps of IAV replication, we found that the downregulation of M6PR expression had no effect on attachment, internalization, early endosome trafficking,or late endosome acidification. However, we found that M6PR expression was critical for the fusion of viral envelope and late endosomal membranes. Of note, M6PR interacted with the hemagglutinin(HA) protein of IAV, and further studies showed that the lumenal domain of M6PR and the ectodomain of HA2 mediated the interaction and directly promoted the fusion of the viral and late endosomal membranes,thereby facilitating IAV replication. Together, our findings highlight the importance of the M6PR–HA interaction in the fusion of viral and late endosomal membranes during IAV replication.

Transmission restriction and genomic evolution co-shape the genetic diversity patterns of influenza A virus

Influenza A virus(IAV)shows an extensive host range and rapid genomic variations,leading to continuous emergence of novel viruses with significant antigenic variations and the potential for cross-species transmission.This causes global pandemics and seasonal flu outbreaks,posing sustained threats worldwide.Thus,studying all IAVs'evolutionary patterns and underlying mechanisms is crucial for effective prevention and control.We developed FluTyping to identify IAV genotypes,to explore overall genetic diversity patterns and their restriction factors.FluTyping groups isolates based on genetic distance and phylogenetic relationships using whole genomes,enabling identification of each isolate's genotype.Three distinct genetic diversity patterns were observed:one genotype domination pattern comprising only H1N1 and H3N2 seasonal influenza subtypes,multi-genotypes cocirculation pattern including majority avian influenza subtypes and swine influenza H1N2,and hybrid-circulation pattern involving H7N9 and three H5 subtypes of influenza viruses.Furthermore,the IAVs in multi-genotypes cocirculation pattern showed region-specific dominant genotypes,implying the restriction of virus transmission is a key factor contributing to distinct genetic diversity patterns,and the genomic evolution underlying different patterns was more influenced by host-specific factors.In summary,a comprehensive picture of the evolutionary patterns of overall IAVs is provided by the FluTyping's identified genotypes,offering important theoretical foundations for future prevention and control of these viruses.

C1QTNF5 is a novel attachment factor that facilitates the entry of influenza A virus

Influenza A virus(IAV)binds sialic acid receptors on the cell surface to enter the host cells,which is the key step in initiating infection,transmission and pathogenesis.Understanding the factors that contribute to the highly efficient entry of IAV into human cells will help elucidate the mechanism of viral entry and pathogenicity,and provide new targets for intervention.In the present study,we reported a novel membrane protein,C1QTNF5,which binds to the hemagglutinin protein of IAV and promotes IAV infection in vitro and in vivo.We found that the HA1 region of IAV hemagglutinin is critical for the interaction with C1QTNF5 protein,and C1QTNF5 interacts with hemagglutinin mainly through its N-terminus(1–103 aa).In addition,we further demonstrated that overexpression of C1QTNF5 promotes IAV entry,while blocking the interaction between C1QTNF5 and IAV hemagglutinin greatly inhibits viral entry.However,C1QTNF5 does not function as a receptor to mediate IAV infection in sialic acid-deficient CHO-Lec2 cells,but promotes IAV to attach to these cells,suggesting that C1QTNF5 is an important attachment factor for IAV.This work reveals C1QTNF5 as a novel IAV attachment factor and provides a new perspective for antiviral strategies.

A novel method to assess antibody-dependent cell-mediated cytotoxicity against influenza A virus M2 in immunized murine models

The matrix protein 2 (M2) is a preferred target for developing a universal vaccine against the influenza A virus (IAV). This study aimed to develop a method for assessing antibody-dependent cell-mediated cytotoxicity (ADCC) associated with M2-based immunization in mice. We first established a stable cell line derived from mouse lymphoma cells (YAC-1) expressing M2 of H3N2. This cell line, designated as YAC-1-M2, was generated using a second-generation lentiviral tricistronic plasmid system to transduce the M2 gene into YAC-1 cells. The ADCC effect induced by polyclonal antibodies targeting matrix protein 2 ectodomain (M2e) was demonstrated by YAC-1-M2 cell lysis by natural killer cells (NK) derived from mice, in the presence of anti-M2 antibodies obtained from mice immunized with an mRNA vaccine based on M2e. This ADCC effect was found to be stronger compared to the effect induced by monoclonal antibodies (14C2) against M2. Moreover, the ADCC effect was enhanced as the effector-to-target ratio of NK to YAC-1-M2 cells increased. In conclusion, we established a novel method to detect ADCC of M2 of IAV, which paves the way for the development of an M2-based universal vaccine against IAV and an in-depth analysis of its mechanism of broad-spectrum immune protection in mice.

Pudilan Xiaoyan oral liquid regulates tissue inflammation and apoptosis in mice with influenza virus pneumonia

Background:The influenza A virus is the primary cause of respiratory infections and poses a global health risk.Pudilan Xiaoyan oral liquid(PDL)exhibits anti-inflammatory and immunomodulatory properties.PDL is commonly employed in clinical practice to manage upper respiratory tract infections.However,there is still much to uncover regarding its potential therapeutic mechanism.Methods:Institute of cancer research mice were infected with influenza A virus via nasal drip.The general state of the mice,lung index,and lung index inhibition rate were used to evaluate the efficacy of PDL.Enzyme-linked immunosorbent assay,western blotting,and immunohistochemistry were used to observe the presence of proteins and cytokines in the lung tissue.Apoptosis was evaluated using the TUNEL assay.Results:PDL improved the mental state of influenza A virus-infected mice,reduced the lung index,and inhibited viral replication.The expression of interleukin-1βand tumor necrosis factor-αwere decreased,whereas the expression of interleukin-10 in the lung tissue was increased due to PDL treatment.In addition,PDL treatment modulated Toll-like receptor 4 and MyD88 expressions in the lung tissues.PDL significantly reduced apoptosis and decreased cleaved caspase-3 and PARP levels,whereas increased B-cell lymphoma-2 expression in the lung tissue.Notably,the moderate-dose group of PDL exhibited a more pronounced effect.These findings indicate that PDL exerts a protective effect against pneumonia injury in influenza A virus-infected mice.Conclusion:PDL inhibited the inflammatory response and regulated apoptosis by regulating Toll-like receptor 4 and MyD88 protein expressions,thereby protecting the lung tissue from viral infection-induced lung tissue injury.