Triggering receptor expressed on myeloid cells 2 (TREM2) serves as an anti-inflammatory receptor, negatively regulating the innate immune response. TREM2 is mainly expressed on dendritic cells and macrophages, the target cells of porcine reproductive and respiratory syndrome virus (PRRSV). Thus, we investigated the potential role of TREM2 in PRRSV infection in porcine alveolar macrophages (PAMs). We found that there was an increased expression of TREM2 upon PRRSV infection in vitro. TREM2 silencing restrained the replication of PRRSV, whereas TREM2 overexpression facilitated viral replication. The cytoplasmic tail domain of TREM2 interacted with PRRSV Nsp2 to promote infection. TREM2 downregulation led to early activation of PI3K/NF-κB signaling, thus reinforcing the expression of proinflammatory cytokines and type I interferons. Due to the enhanced cytokine expression, a disintegrin and metalloproteinase 17 was activated to promote the cleavage of membrane CD163, which resulted in suppression of infection. Furthermore, exogenous soluble TREM2 (sTREM2)-mediated inhibition of PRRSV attachment might be attributed to its competitive binding to viral envelope proteins. In pigs, following PRRSV challenge in vivo, the expression of TREM2 in lungs and lymph nodes as well as the production of sTREM2 were significantly increased. These novel findings indicate that TREM2 plays a role in regulating PRRSV replication via the inflammatory response. Therefore, our work describes a novel antiviral mechanism against PRRSV infection and suggests that targeting TREM2 could be a new approach in the control of the PRRSV infection. Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most important pathogens in the global swine industry and is difficult to control. CD163 is a receptor that is required for PRRSV infection, and its expression is regulated by various inflammatory mediators. Triggering receptor expressed on myeloid cells 2 (TREM2) is a novel immunoregulatory receptor, which is involved in innate immunity and anti-inflammatory responses. Here we sought to elucidate whether TREM2 regulates CD163 expression to promote PRRSV infection via the inflammatory response. We found increased TREM2 levels upon PRRSV infection in vitro and in vivo in the lungs and lymph nodes of infected pigs. We demonstrated that the cytoplasmic tail of TREM2 interacts with PRRSV Nsp2 to promote infection. Additionally, TREM2 silencing triggers an early proinflammatory response via PI3K/NF-κB pathway, thus downregulating the expression of CD163, which leads to virus suppression. Our work provides a novel antiviral mechanism against PRRSV infection and suggests that targeting TREM2 could be a new approach for control of the disease.

Porcine reproductive and respiratory syndrome virus (PRRSV) 1 and 2 differ in their recognition of CD163. Substitution of porcine CD163 SRCR5 domain with a human CD163-like SRCR8 confers resistance to PRRSV 1 but not PRRSV 2. The deletion of CD163 SRCR5 has been shown to confer resistance to PRRSV 1 in vivo and both PRRSV 1 and 2 in vitro. However, the anti-PRRSV 2 activity of modifying the CD163 SRCR5 domain has not yet been reported. Here, we describe the highly efficient generation of two pig breeds (Liang Guang Small Spotted and Large White pigs) lacking a short region of CD163 SRCR5, including the ligand-binding pocket. We generated a large number of gene-edited Large White pigs of the F0 generation for use in viral challenge studies. The results of this study show that these pigs are completely resistant to infection by species 2 PRRSV, JXA1, and MY strains. There were no clinical symptoms, pathological abnormalities, viremia, or anti-PRRSV antibodies in the CD163 SRCR5-edited pigs compared to wild-type controls after viral challenge. Porcine alveolar macrophages (PAMs) isolated from CD163 SRCR5-edited Large White pigs also displayed resistance to PRRSV in vitro. In addition, CD163 SRCR5-edited PAMs still exhibited a cytokine response to PRRSV infection, and no significant difference was observed in cytokine expression compared to wild-type PAMs. Taken together, these data suggest that CD163 SRCR5-edited pigs are resistant to PRRSV 2, providing a basis for the establishment of PRRSV-resistant pig lines for commercial application and further investigation of the essential region of SRCR5 involved in virus infection.

Porcine alveolar macrophages without the CD163 SRCR5 domain are resistant to porcine reproductive and respiratory syndrome virus (PRRSV) infection. However, whether the deletion of CD163 SRCR5 in MARC-145 cells confers resistance to PRRSV and interaction of which of the host proteins with CD163 is involved in virus uncoating remain unclear. Here we deleted the SRCR5 domain of CD163 in MARC-145 cells using CRISPR/Cas9 to generate a CD163^ΔSRCR5 MARC-145 cell line. The modification of CD163 had no impact on CD163 expression. CD163^ΔSRCR5 cells were completely resistant to infection by PRRSV-2 strains Li11, CHR6, TJM, and VR2332. The modified cells showed no cytokine response to PRRSV-2 infection and maintained normal cell vitality comparable with the WT cells. The resistant phenotype of the cells was stably maintained through cell passages. There were no replication transcription complexes in the CD163^ΔSRCR5 cells. SRCR5 deletion did not disturb the colocalization of CD163 and PRRSV-N in early endosomes (EE). However, the interaction of the viral proteins GP2a, GP3, or GP5 with CD163, which is involved in virus uncoating was affected. Furthermore, 77 CD163-binding cellular proteins affected by the SRCR5 deletion were identified by LC–MS/MS. Inhibition of calpain 1 trapped the virions in EE and forced then into late endosomes but did not block viral attachment and internalization, suggesting that calpain 1 is involved in the uncoating. Overall, CD163^ΔSRCR5 MARC-145 cells are fully resistant to PRRSV-2 infection and calpain 1 is identified as a novel host protein that interacts with CD163 to facilitate PRRSV uncoating.

To express the antimicrobial peptide cecropin D in Pichia pastoris and determine the activity of the expressed product, four oligonucleotide fragments were synthesized in accordance with the available cecropin D sequences and a codon bias suitable for Pichia pastoris. Sequence fragments were phosphorylated, annealed, linked and cloned into the expression vector pGAPZαA and the yeast α‑mating factor signal peptide was used as the signal sequence. The P. pastoris SMD1168 cells were transformed by electroporation using the constructed recombinant plasmid pGAPZαA‑cecropin D. We were able to demonstrate by PCR that the cecropin D sequence had integrated into the P. pastoris genome. The expressed and secreted product was identified using Tricine‑SDS‑PAGE. Antibacterial activity was demonstrated using an agarose diffusion test and turbidimetry. The molecular mass of the recombinant cecropin D was estimated to be 3,900 Da. The recombinant cecropin D exhibited antibacterial activity for both Gram‑positive and Gram‑negative bacteria, suggesting that cecropin D was successfully expressed in P. pastoris. This approach holds great promise for antibacterial drug development.

Persistent infection of porcine reproductive and respiratory syndrome virus (PRRSV) significantly hampers both the quantity and quality of pork production in China. Although PRRSV is widely prevalent worldwide, the absence of effective vaccines has made it one of the major pathogens threatening the sustainable development of the global swine industry. Vaccination remains one of the most effective measures for controlling pathogen infections. However, the continuous genetic recombination and mutation of PRRSV demand more comprehensive strategies to address emerging threats, while ensuring the efficacy and safety of vaccines. This review provides an overview of the latest advances in PRRSV vaccine research, highlighting the importance of understanding the unique strengths and limitations of various vaccines in developing effective therapeutic approaches and vaccination strategies. Moreover, the development of adjuvants and antiviral drugs as adjuncts to combat PRRSV infection offers significant potential for enhancing disease control efforts. With the advancement of technologies such as proteolysis-targeting chimera (PROTAC) and mRNA, new avenues for controlling PRRSV and other pathogens are emerging, offering considerable hope. Ultimately, the goal of these vaccine developments is to alleviate the impact of PRRSV on animal health and the profitability of the swine industry.

Porcine reproductive and respiratory syndrome virus (PRRSV) continues to cause substantial economic losses to the pig industry worldwide. Heparan sulfate (HS) is used by PRRSV for initial attachment to target cells. However, the role of HS in the late phase of PRRSV infection and the mechanism of virus release from host cells remain largely unknown. In this study, we showed that PRRSV infection caused a decrease in HS expression and upregulated heparanase, the only known enzyme capable of degrading HS. We subsequently demonstrated that the NF-κB signaling pathway and cathepsin L protease were involved in regulation of PRRSV infection-induced heparanase. In addition, we found that ablation of heparanase expression using small interfering RNA duplexes increased cell surface expression of HS and suppressed PRRSV replication and release, whereas overexpression of heparanase reduced HS surface expression and enhanced PRRSV replication and release. These data suggest that PRRSV activates NF-κB and cathepsin L to upregulate and process heparanase, and then the active heparanase cleaves HS, resulting in viral release. Our findings provide new insight into the molecular mechanism of PRRSV egress from host cells, which might help us to further understand PRRSV pathogenesis. IMPORTANCE Porcine reproductive and respiratory syndrome virus (PRRSV) causes great economic losses each year to the pig industry worldwide. The molecular mechanism of PRRSV release from host cells largely remains a mystery. In this study, we demonstrate that PRRSV activates NF-κB and cathepsin L to upregulate and process heparanase, and then the active heparanase is released to the extracellular space and exerts enzymatic activity to cleave heparan sulfate, resulting in viral release. Our findings provide new insight into the molecular mechanism of PRRSV egress from host cells, which might help us to further understand PRRSV pathogenesis.