Enhanced immune response of BMDCs pulsed with H9N2 AIV and CpG

A double-edged sword in antiviral defence: ATG7 binding dicer to promote virus replication

RNA interference (RNAi) and autophagy are two pivotal biological processes that regulate virus replication. This study explored the complex relationship between autophagy and RNAi in controlling influenza virus replication. Initially, we reported that influenza virus (H9N2) infection increases the viral load and the expression of autophagy markers while inhibiting the RNAi pathway. Subsequent studies employing autophagy enhancer and inhibitor treatments confirmed that avian influenza virus (AIV, H9N2) promotes viral replication by enhancing autophagy pathways. Further analysis revealed that ATG7, an autophagy protein, can interact with dicer to affect its antiviral functions. Finally, we discovered that infection with other avian RNA viruses, including infectious bursal disease virus (IBDV) and infectious bronchitis virus (IBV), induced the upregulation of ATG7, which blocked the RNAi pathway to facilitate virus replication. Our findings suggested that virus infection might trigger the upregulation of autophagy and downregulation of the RNAi pathway, revealing a complex interaction between these two biological processes in the defence against viral replication.

Delivery of dendritic cells targeting 3M2e-HA2 nanoparticles with a CpG adjuvant via lysosomal escape of Salmonella enhances protection against H9N2 avian influenza virus

Avian influenza virus (AIV) subtype H9N2 still poses a great threat to the poultry farming industry and public health worldwide, and the development of a new influenza vaccine that is safe and conservative and able to address influenza virus mutations is highly promising for application. HA2, the neck of the HA protein, and M2e, the extracellular N-terminal structural domain of the M2 protein, are conserved and effective protective antigens. In this study, the HA2 sequences were fused with three M2e copies (H9N2, H1N1 and H5N1) to the norovirus VP1 protein via the SpyTag-SpyCatcher platform to form self-assembled nanoparticles and display antigenic proteins on its surface, yielding pYL262. The chicken dendritic cells (DCs) targeting the nanobody phage-54 were then fused to HA2-3M2e to yield pYL327. Finally, a synthesized 20-repeat CpG adjuvant gene fragment was inserted into pYL327, resulting in the plasmid pYL331. All the constructed plasmids were then transformed into the sifA gene-deficient Salmonella vector χYL56 for oral immunization. The results showed that sifA-deficient Salmonella could efficiently increase antigen-specific mucosal sIgA antibody titers, especially in alveolar lavage samples, whereas the presence of the phage-54 nanobody could dramatically increase intracellular IFN-γ mRNA levels, indicating its ability to enhance the Th1-type immune response. Finally, the presence of the CpG adjuvant clearly increased T-cell proliferation and promoted DC activation, with elevated splenic TLR21 levels observed. Strikingly, after oral immunization with χYL56 (pYL331), chickens were protected against challenge with the G57 genotype H9N2 virus, which presented similar or even better levels of virus shedding and body weight gain compared with the commercial inactivated vaccine, providing a new option for controlling H9N2 virus infection in the future.

IBV QX affects the antigen presentation function of BMDCs through nonstructural protein16

The gamma-coronavirus infectious bronchitis virus (IBV) has a high mutation rate and mainly invades the respiratory mucosa, making it difficult to prevent and causing great economic losses. Nonstructural protein 16 (NSP16) of IBV QX also not only plays an indispensable role in virus invading but also might hugely influence the antigen's recognition and presentation ability of host BMDCs. Hence, our study tries to illustrate the underline mechanism of how NSP16 influences the immune function of BMDCs. Initially, we found that NSP16 of the QX strain significantly inhibited the antigen presentation ability and immune response of mouse BMDCs, which was stimulated by Poly (I:C) or AIV RNA. Besides mouse BMDCs, we also found that NSP16 of the QX strain also significantly stimulated the chicken BMDCs to activate the interferon signaling pathway. Furthermore, we preliminarily demonstrated that IBV QX NSP16 inhibits the antiviral system by affecting the antigen-presenting function of BMDCs.

miR29a and miR378b Influence CpG-Stimulated Dendritic Cells and Regulate cGAS/STING Pathway

The Cytosine–phosphate–guanosine (CpG) motif, which is specifically recognized intracellularly by dendritic cells (DCs), plays a crucial role in regulating the innate immune response. MicroRNAs (miRNAs) can strongly influence the antigen-presenting ability of DCs. In this study, we examine the action of miRNAs on CpG-stimulated and control DCs, as well as their effect on cyclic guanosine monophosphate-adenosine monophosphate (GMP–AMP) synthase (cGAS) and the stimulator of interferon genes (STING) signal pathway. Firstly, we selected miRNAs (miR-29a and miR-378b) based on expression in CpG-stimulated mouse bone marrow-derived dendritic cells (BMDCs). Secondly, we investigated the functions of miR-29a and miR-378b on CpG-stimulated and unstimulated BMDCs. The results showed that miR-29a and miR-378b increased expression of both the immunoregulatory DC surface markers (CD86 and CD40) and the immunosuppressive molecule CD273 by DCs. Thirdly, cytokine detection revealed that both miR-29a and miR-378b enhanced interferon-β (IFN-β) expression while suppressing tumor necrosis factor-α (TNF-α) production. Finally, our results suggest that miR-378b can bind TANK-binding kinase binding protein 1 (TBKBP1) to activate the cGAS/STING signaling pathway. By contrast, miR-29a targeted interferon regulatory factor 7 (IRF7) and promoted the expression of STING. Together, our results provide insight into the molecular mechanism of miRNA induction by CpG to regulate DC function.

MiR674 inhibits the neuraminidase-stimulated immune response on dendritic cells via down-regulated Mbnl3

Neuraminidase (NA), a structural protein of the H9N2 avian influenza virus (H9N2 AIV), can facilitate viral invasion of the upper airway by cleaving the sialic acid moieties on mucin. Dendritic cells (DCs) are major antigen-presenting cells whose immune functions, such as presenting antigens and activating lymphocytes, can be regulated by microRNAs. Here, we studied the molecular mechanism of miRNA-induced repression of immune responses in mouse DCs. First, we screened for and verified the miRNAs induced by NA. Then, we showed that, consistent with the H9N2 virus treatment, the viral NA up-regulated the expression of miR-155, miR-674, and miR-499 in DCs; however, unlike H9N2 virus treatment, the presence of NA was associated with reduced expression of miR-181b1. Our results suggest that NA significantly increased DC surface markers CD80 and MHCII and enhanced the ability of activating lymphocytes and secreting cytokines compared with HA, NP and M2. Meanwhile, we found that miR-674 and miR-155 over-expression increased all surface markers of DC. Nevertheless, by inhibiting the expression of miR-674 and miR-155, NA lost the ability to promote DC maturation. Furthermore, we predicted and demonstrated that Pgm2l1, Aldh18a1, Camk1d, and Mbnl3 were the target genes of miR-674. Among them, Mbnl3 interference strongly blocked the mature DCs. Collectively, our data shed new light on the roles of and mechanisms involved in the repression of DCs by miRNAs, which may contribute to efforts to develop a prophylaxis for the influenza virus.

H9N2 Avian Influenza Virus Protein PB1 Enhances the Immune Responses of Bone Marrow-Derived Dendritic Cells by Down-Regulating miR375

Polymerase basic protein 1 (PB1), the catalytic core of the influenza A virus RNA polymerase complex, is essential for viral transcription and replication. Dendritic cells (DCs) possess important antigen presenting ability and a crucial role in recognizing and clearing virus. MicroRNA (miRNA) influence the development of DCs and their ability to present antigens as well as the ability of avian influenza virus (AIV) to infect host cells and replicate. Here, we studied the molecular mechanism underlying the miRNA-mediated regulation of immune function in mouse DCs. We first screened for and verified the induction of miRNAs in DCs after PB1 transfection. Results showed that the viral protein PB1 down-regulated the expression of miR375, miR146, miR339, and miR679 in DCs, consistent with the results of H9N2 virus treatment; however, the expression of miR222 and miR499, also reduced in the presence of PB1, was in contrast to the results of H9N2 virus treatment. Our results suggest that PB1 enhanced the ability of DCs to present antigens, activate lymphocytes, and secrete cytokines, while miR375 over-expression repressed activation of DC maturation. Nevertheless, PB1 could not promote DC maturation once miR375 was inhibited. Finally, we revealed that PB1 inhibited the P-Jnk/Jnk signaling pathway, but activated the p-Erk/Erk signaling pathway. While inhibition of miR375 -activated the p-Erk/Erk and p-p38/p38 signaling pathway, but repressed the P-Jnk/Jnk signaling pathway. Taken together, results of our studies shed new light on the roles and mechanisms of PB1 and miR375 in regulating DC function and suggest new strategies for combating AIV.

H9N2 avian influenza virus enhances the immune responses of BMDCs by down-regulating miR29c

Avian influenza virus (AIV) of the subtypes H9 and N2 is well recognised and caused outbreaks-due to its high genetic variability and high rate of recombination with other influenza virus subtypes. The pathogenicity of H9N2 AIV depends on the host immune response. Dendritic cells (DCs) are major antigen presenting cells that can significantly inhibit H9N2 AIV replication. MicroRNAs (miRNAs) influence the ability of DCs to present antigens, as well as the ability of AIVs to infect host cells and replicate. Here, we studied the molecular mechanism underlying the miRNA-mediated regulation of immune function of mouse DCs. We first screened for and verified the induction of miRNAs in DCs after H9N2 AIVstimulation. We also constructed miR29c, miR339 and miR222 over-expression vector and showed that only the induction of miR29c lead to a hugely increased expression of surface marker MHCII and CD40. Whilst the inhibition of miR29c, miR339 and miR222 in mouse DCs would repressed the expression of DCs surface markers. Moreover, we found that miR29c stimulation not only up-regulate MHCII and CD40, but also enhance the ability of DCs to activate lymphocytes and secrete cytokines IL-6 or TNF-a. Furthermore, we found that Tarbp1 and Rfx7 were targeted and repressed by miR29c. Finally, we revealed that the inhibition of miR29c marvelously accelerated virus replication. Together, our data shed new light on the roles and mechanisms of miR29c in regulating DC function and suggest new strategies for combating AIVs.

Genome-wide profiling of chicken dendritic cell response to infectious bursal disease

BACKGROUND

Avian infectious bursal disease virus (IBDV) is a highly contagious, immunosuppressive disease of young chickens, which causes high mortality rates and large economic losses in the poultry industry. Dendritic cells (DCs), which are antigen-presenting cells, have the unique ability to induce both innate and acquired immune responses and may significantly influence virus pathogenicity. To understand the interaction between IBDV and DCs, a microarray was used to analyse the response of DCs infected by IBDV.

RESULTS

IBDV infection induced 479 upregulated and 466 downregulated mRNAs in chicken DCs. Analysis of Gene Ontology suggested that transcription from the RNA polymerase II promoter and the RNA biosynthetic process were enriched, and pathway analyses suggested that oxidative phosphorylation, as well as the T cell receptor and Interleukin-17 (IL-17) signalling pathways might be activated by IBDV infection. Moreover, microRNA (miRNA) and long non-coding RNA (lncRNA) alterations in IBDV-infected chicken DCs were observed. A total of 18 significantly upregulated or downregulated miRNAs and 441 significantly upregulated or downregulated lncRNAs were identified in IBDV-stimulated DCs. We constructed 42 transcription factor (TF)-miRNA-mRNA interactions involving 1 TF, 3 miRNAs, and 42 mRNAs in IBDV-stimulated DCs. Finally, we predicted the target genes of differentially expressed lncRNAs, and constructed lncRNA-mRNA regulatory networks.

CONCLUSIONS

The results of this study suggest a mechanism to explain how IBDV infection triggers an effective immune response in chicken DCs.

Whole inactivated avian Influenza H9N2 viruses induce nasal submucosal dendritic cells to sample luminal viruses via transepithelial dendrites and trigger subsequent DC maturation

Nasal mucosal barrier is a key impediment for the absorption of influenza whole inactivated virus (WIV) intranasal vaccine. Yet it is still unclear how WIV cross the epithelial cells (ECs) in nasal cavity. Here, in vitro, a coculture system was well established, consisting of surrogate nasal ECs (Calu-3) and dendritic cells (DCs). After adding H9N2 WIV on the apical side of ECs, we found that submucosal DCs extended their transepithelial dendrites (TEDs) and sampled luminal viruses. However, ECs were not involved in the transepithelial transport of viruses. Subsequently, the phenotypic and functional maturation of DCs were also enhanced, whereas they were attenuated after blocking of TED formation by anti-JAM1 antibody. In vivo, we confirmed that H9N2 WIV were capable of inducing nasal submucosal DCs to sample luminal viruses via TEDs in the nasal passage but not nasal-associated lymphoid tissue (NALT). CD103(+) and CD103(-) DC subsets participated in this process. Of note, chemokine CCL20, released from the H9N2 WIV-induced ECs, played a vital role in DC recruitment and TED formation. Taken together, our findings indicated that TEDs played a critical role in facilitating viral transport across the epithelial barrier, which may guide the design of novel nasal mucosal vaccine strategies.