Development of a monoclonal antibody against swine leukocyte antigen (SLA)-DR α chain and evaluation of SLA-DR expression in bone marrow-derived dendritic cells after PRRSV infection

Monoclonal Antibody against Porcine LAG3 Inhibits Porcine Reproductive and Respiratory Syndrome Virus Infection

Lymphocyte activation gene 3 (LAG3) is an inhibitory receptor and the interaction between fibrinogen-like protein 1 and LAG3 can inhibit the anti-tumor effect of T cells both in vivo and in vitro, which was regarded as a new immune evasion mechanism. Porcine reproductive and respiratory syndrome (PRRS), caused by PRRSV, is an infectious disease characterized by reproductive disorders in pregnant sows and gilts and respiratory problems in pigs of all ages, seriously impacting the pig industry worldwide. In this study, monoclonal antibodies (mAbs) against porcine LAG3 (pLAG3) were developed, and one mAb (1C2) showed good reactivity with pLAG3 on PHA-activated porcine peripheral blood lymphocytes. Epitope mapping showed the epitope recognized by mAb 1C2 was located at amino acid residues 214-435 of pLAG3. LAG3 expression in the tissues of PRRSV-infected pigs was detected, using mAb 1C2 as the primary antibody, and the results revealed that PRRSV infection caused a marked increase in LAG3 expression compared to the control group. Interference of LAG3 expression on PHA-activated lymphocytes promoted PRRSV replication in the co-culture system of monocyte-derived dendritic cells and lymphocytes, whereas overexpression of LAG3 or blocking of the LAG3 signal with mAb 1C2 inhibited PRRSV replication, indicating that PRRSV infection activates the LAG3-signaling pathway, suggesting that this pathway plays an important role in PRRSV pathogenesis. The results obtained lay the foundation for subsequent research on the role of LAG3 in PRRS and other diseases with persistent infection characteristics.

The DACH1 Gene Transcriptional Activation and Protein Degradation Mediated by Transactivator Tas of Prototype Foamy Virus

Foamy viruses are members of the Retroviridae family's Spumaretrovirinae subfamily. They induce cell vacuolation and exhibit a foamy pathogenic impact after infecting cells. DACH1 (dachshund family transcription factor 1) is a crucial cytokine linked to tumor development, and is associated with the growth of many different malignant tumor cells. Additionally, DACH1 suppresses pancreatic cell proliferation and is involved in diabetes insulin signaling. Prototype foamy viruses (PFVs) were used for the investigation of the regulatory mechanism of FVs on cellular DACH1 expression. The results show that DACH1 expression in PFV-infected cells was inconsistent at both the transcriptional and protein levels. At the transcriptional level, DACH1 was significantly activated by PFV transactivator Tas, and dual-luciferase reporter gene tests, EMSA, and ChIP assays found a Tas response element of 21 nucleotides in the DACH1 promoter. PFV and Tas did not boost the levels of DACH1 protein in a manner consistent with the high levels of DACH1 transcription expression. It was noted that Tas increased the expression of the Ser/Thr protein phosphatase PPM1E, causing PPM1E-mediated post-translational SUMOylation alterations of DACH1 to prompt DACH1 to degrade. The reason for DACH1 protein degradation is that DACH1 inhibits PFV replication. To sum up, these findings show that PFV upregulated the transcription of DACH1, while urging its protein into PPM1E-mediated SUMOylation, to eliminate the adverse effect of DACH1 overexpression of host cells on viral replication and promote virus survival.

Quantitative Proteomic Analysis of Tibetan Pig Livers at Different Altitudes

In this study, the differences in protein profiles between the livers of Shannan Tibetan pigs (SNT), Linzhi Tibetan pigs (LZT) and Jiuzhaigou Tibetan pigs (JZT) were comparatively analyzed by tandem mass spectrometry-labeling quantitative proteomics. A total of 6804 proteins were identified: 6471 were quantified and 1095 were screened as differentially expressed proteins (DEPs). Bioinformatics analysis results show that, compared with JZT livers, up-regulated DEPs in SNT and LZT livers mainly promoted hepatic detoxification through steroid hormone biosynthesis and participated in lipid metabolism to maintain body energy homeostasis, immune response and immune regulation, while down-regulated DEPs were mainly involved in lipid metabolism and immune regulation. Three proteases closely related to hepatic fatty acid oxidation were down-regulated in enzymatic activity, indicating higher levels of lipid oxidation in SNT and LZT livers than in JZT livers. Down-regulation of the expression of ten immunoglobulins suggests that JZT are more susceptible to autoimmune diseases. It is highly likely that these differences in lipid metabolism and immune-related proteins are in response to the ecological environment at different altitudes, and the findings contribute to the understanding of the potential molecular link between Tibetan pig livers and the environment.

Evaluation of porcine GM-CSF during PRRSV infection in vitro and in vivo indicating a protective role of GM-CSF related with M1 biased activation in alveolar macrophage during PRRSV infection

Granulocyte-macrophage colony stimulating factor (GM-CSF), participates in diverse biological processes associated with innate and adaptive immunity, has unknown effects during PRRSV infection. Here, a double-antibody sandwich ELISA for pGM-CSF was developed in-house for evaluation of pGM-CSF level during PRRSV infection both in vitro and in vivo. In in vitro assay, it was notable that PRRSV-infected porcine alveolar macrophages (PAMs) yielded inconsistent pGM-CSF protein- and mRNA-level, suggesting a post-transcriptional inhibition of pGM-CSF mRNA was employed by PRRSV. Meanwhile, concurrent analysis of pGM-CSF levels in serum samples from PRRSV-infected piglets suggested that effect of PRRSV infection demonstrated minimum effect on pGM-CSF levels regardless of PRRSV virulence phenotypes. Moreover, in vitro treatment of PAMs with pGM-CSF prior PRRSV inoculation did not inhibit PRRSV replication in PAMs although genes downstream of pGM-CSF in PAMs could be upregulated by pGM-CSF treatment. Meanwhile, knockdown of pGM-CSF using siRNA did not enhance PRRSV replication as well. Intriguingly, therapeutic antibody treatment of HP-PRRSV-infected piglets led to significantly increased serum pGM-CSF levels, thus aligning with low pneumonia incidence and low intracellular PRRSV-RNA levels in PAMs of therapeutic antibody treated piglets. Furthermore, transcriptome analysis of PAMs from infected piglets revealed increased serum pGM-CSF levels correlated with activation of downstream signal of pGM-CSF in PAMs as evidenced by a M1-like phenotypes of gene expression pattern, implying a potential host-protective role played by pGM-CSF for PRRSV infection in vivo. In conclusion, our results demonstrated developments of a highly sensitive and specific ELISA for pGM-CSF and revealed a potential protective role conferred by pGM-CSF during PRRSV infection.

Porcine Epidemic Diarrhea Virus Envelope Protein Blocks SLA-DR Expression in Barrow-Derived Dendritic Cells by Inhibiting Promoters Activation

Porcine epidemic diarrhea (PED) is an acute, highly contagious intestinal swine disease caused by porcine epidemic diarrhea virus (PEDV). In addition to known PEDV infection targets (villous small intestinal epithelial cells), recent reports suggest that dendritic cells (DCs) may also be targeted by PEDV in vivo. Thus, in this study we used bone marrow-derived dendritic cells (BM-DCs) as an in vitro model of antigen-presenting cells (APCs). Our results revealed that PEDV replicated in BM-DCs and that PEDV infection of cells inhibited expression of swine leukocyte antigen II DR (SLA-DR), a key MHC-II molecule involved in antigen presentation and initiation of CD4⁺ T cell activation. Notably, SLA-DR inhibition in BM-DCs did not require PEDV replication, suggesting that PEDV structural proteins participated in SLA-DR transcriptional inhibition. Moreover, reporter assay-based screening indicated that PEDV envelope protein blocked activation of SLA-DRα and β promoters, as did PEDV-ORF3 protein when present during PEDV replication. Meanwhile, treatment of PEDV-infected BM-DCs with MG132, a ubiquitin-proteasome degradation pathway inhibitor, did not restore SLA-DR protein levels. Additionally, PEDV infection of BM-DCs did not alter SLA-DR ubiquitination status, suggesting that PEDV infection did not affect SLA-DR degradation. Furthermore, additions of PEDV structural proteins to HEK-293T-SLA-DR stably transfected cells had no effect on SLA-DR protein levels, indicating that PEDV-mediated inhibition of SLA-DR expression acted mainly at the transcriptional level, not at the protein level. These results provide novel insights into PEDV pathogenic mechanisms and viral-host interactions.

Porcine Reproductive and Respiratory Syndrome Virus Promotes SLA-DR-Mediated Antigen Presentation of Nonstructural Proteins To Evoke a Nonneutralizing Antibody Response In Vivo

The humoral immune response against porcine reproductive and respiratory syndrome virus (PRRSV) infection is characterized by a rapid induction of nonneutralizing antibodies (non-NAbs) against nonstructural proteins (NSPs). Here, we systematically investigated the potential mechanism for the induction of PRRSV NSP-specific non-NAbs. Our data suggested that PRRSV NSP-specific antibodies appeared within 10 days after PRRSV infection in vivo In the in vitro model, functional upregulation of swine leukocyte antigen (SLA)-DR was observed in bone marrow-derived dendritic cells (BMDCs) and porcine alveolar macrophages (PAMs), whereas remarkable inhibition at the mRNA level was observed after infection by both PRRSV-1 and PRRSV-2 isolates. Notably, the inconsistency in SLA-DR expression between the mRNA and protein levels resulted from deubiquitination of SLA-DR via the ovarian tumor (OTU) domain of PRRSV NSP2, which inhibited ubiquitin-mediated degradation. Moreover, mass spectrometry-based immunopeptidome analysis identified immunopeptides originating from multiple PRRSV NSPs within SLA-DR of PRRSV-infected BMDCs. Meanwhile, these PRRSV NSP-derived immunopeptides could be specifically recognized by serum from PRRSV-infected piglets. Notably, certain NSP-derived immunopeptides characterized in vitro could be identified from PAMs or hilar lymph nodes from PRRSV-infected piglets. More importantly, an in vitro neutralizing assay indicated that serum antibodies against NSP immunopeptides were unable to neutralize PRRSV in vitro Conversely, certain structural protein (SP)-derived immunopeptides were identified and could be recognize by pig hyperimmune serum against PRRSV, which further indicates that the NSP-derived antibody response is nonprotective in vivo In conclusion, our data suggested that PRRSV infection interferes with major histocompatibility complex class II (MHC-II) molecule-mediated antigen presentation in antigen-presenting cells (APCs) via promoting SLA-DR expression to present immunopeptides from PRRSV NSPs, which contributes to the induction of non-NAbs in vivo IMPORTANCE PRRSV has haunted the swine industry for over 30 years since its emergence. Besides the limited efficacy of PRRSV modified live vaccines (MLVs) against heterogeneous PRRSV isolates, rapid induction of nonneutralizing antibodies (non-NAbs) against PRRSV NSPs after MLV immunization or wild-strain infection is one of the reasons why development of an effective vaccine has been hampered. By using in vitro-generated BMDCs as models to understand the antigen presentation process of PRRSV, we obtained data indicating that PRRSV infection of BMDCs promotes functional SLA-DR upregulation to present PRRSV NSP-derived immunopeptides for evoking a non-NAb response in vivo Our work not only uncovered a novel mechanism for interference in host antigen presentation by PRRSV but also revealed a novel insight for understanding the rapid production of nonneutralizing antibodies against PRRSV NSPs, which may have benefit for developing an effective vaccine against PRRSV in the future.

Downregulation of miR-155-5p facilitates enterovirus 71 replication through suppression of type I IFN response by targeting FOXO3/IRF7 pathway

Enterovirus 71 (EV71), the major cause of hand-foot-and-mouth disease (HFMD), has evolved diverse strategies to counter the type I interferon (IFN-I) response during infection. Recently, microRNAs have regulatory roles in host innate immune responses to viral infections; however, whether EV71 escapes the IFN-I antiviral response through regulation of miRNAs remains unclear. Using a microarray assay, microRNA-155-5p (miR-155-5p) was found to be significantly up-regulated in serum from patients with EV71 infection and the increased expression of miR-155-5p was further confirmed in vivo and in vitro in response to EV71 infection. miR-155-5p overexpression suppressed EV71 titers and VP1 protein level, while miR-155-5p inhibition had an opposite result. Moreover, we found that miR-155-5p overexpression enhanced EV71 triggered IFN I production and the expressions of IFN-stimulated genes (ISGs), while inhibition of miR-155-5p suppressed these processes. Furthermore, bioinformatics analysis and luciferase reporter assay demonstrated that miR-155-5p directly targeted forkhead box protein O3 (FOXO3) and negatively regulated FOXO3/IRF7 axis, an important regulatory pathway for type I IFN production during EV71 infection. Inhibition of FOXO3 reversed the effects of miR-155-5p inhibitor on EV71 replication and the type I IFN production. Importantly, in EV71 infection mice, agomir-155-5p injection resulted in a significant reduction of viral VP1 protein expressions in brain and lung tissues, increased IFN-α/β production and increased mice survival rate. In contrast, antagomir-155-5p enhanced EV71 induced these effects. Collectively, our study indicates that weaken miR-155-5p facilitates EV71 replication through suppression of type I IFN response by FOXO3/IRF7 pathway, thereby suggesting a novel strategy for developing effective antiviral therapy.