Porcine alveolar macrophage polarization is involved in inhibition of porcine reproductive and respiratory syndrome virus (PRRSV) replication

Abstract

Macrophage polarization is a process by which macrophages acquire a distinct phenotypic and functional profile in response to microenvironmental signals. The classically and alternatively activated (M1 and M2, respectively) macrophage phenotypes are defined by the specific molecular characteristics induced in response to prototypic pro- and anti-inflammatory cues. In this study, we used LPS/IFN-γ and IL-4 to stimulate porcine alveolar macrophages (PAMs) in vitro and investigated the expression changes of several novel markers during macrophage polarization. Notably, we found that LPS/IFN-γ-stimulated PAMs express prototypical M1 molecules, whereas IL-4-stimulated PAMs express M2 molecules. We also demonstrated that replication of the highly pathogenic porcine reproductive and respiratory syndrome virus (PRRSV) strain HuN4 was effectively suppressed in LPS/IFN-γ-stimulated M1 PAMs (M1 type), but not IL-4 stimulated M2 PAMs. However, this was not observed with the classic, less pathogenic CH-1a strain. Moreover, we found that M2 marker expression gradually increased after PAM infection with PRRSV, whereas no significant changes were found with M1 marker expression, suggesting that PRRSV infection may skew macrophage polarization towards an M2 phenotype. Finally, we found that anti-viral cytokine expression was significantly higher in M1 macrophages than in M2 macrophages or nonpolarized controls. In summary, our results show that PRRSV replication was significantly impaired in M1 PAMs, which may serve as a foundation for further understanding of the dynamic phenotypic changes during macrophage polarization and their effects on viral infection.

Lipopolysaccharide Downregulates CD163 Expression to Inhibit PRRSV Infection via TLR4-NF-κB Pathway

“…On the contrary, macrophages are polarized to M2 phenotype following IL-4, IL-10, or IL-13 stimulation, which triggers anti-inflammatory response (Gordon, 2003). Previous studies have shown that PAMs polarized toward M1 phenotype significantly inhibit PRRSV replication (Wang et al, 2017). In our work, LPS-treated PAMs appeared enhanced expression of proinflammatory cytokines, including IL-1β, IL-6, IL-8, and TNF-α, which are prototypical M1 macrophage markers (Figure 3).…”

“…TLR4-MD2-LPS complex initiates signal transduction of IRF3 and NF-κB and consequently leads to secretion of type I interferon and inflammatory cytokines (Kawai and Akira, 2010). Moreover, LPS-stimulated PAMs polarizes toward M1 PAMs, which significantly inhibits PRRSV replication, but it remains an unclear mechanism (Wang et al, 2017).…”

Hypothalamus-pituitary-adrenal axis involves in anti-viral ability through regulation of immune response in piglets infected by highly pathogenic porcine reproductive and respiratory syndrome virus

“…In contrast, DEX inhibited the inflammation induced by HP-PRRSV, although the levels of proinflammatory cytokines in the peripheral blood were significantly decreased and long-lasting high fever and lung lesions were also observed in these HuN4-infected piglets. Despite the solvent of RU486 contained 50% ethanol (30 mg/ml), the dose used for each piglet was no more than 0.1 g/kg b.w., which has been demonstrated to have neither significant effect on the plasma cortisol levels nor anti-viral cell-mediate immune response, as well as no perceptible depression of the central nervous system [22,25]. Thus, we believe that DEX induces immunosuppression during HP-PRRSV infection, allowing enhanced viral replication and leading to high mortality.…”

“…The HP-PRRSV HuN4 strain (GenBank accession no. EF635006) was used in this study as a viral inoculum after three passages through porcine alveolar macrophages (PAMs, which were isolated using a lung lavage technique from 4 to 6-week-old specific-pathogen-free piglets that were free of PRRSV, PCV 2 , CSFV, PPV, PRV, swine influenza virus, and Mycoplasma hyopneumoniae infections as previously described [22]) with a titer of 10 5.0 TCID 50 /mL [23].…”

Dietary plant extracts modulate gene expression profiles in alveolar macrophages of pigs experimentally infected with porcine reproductive and respiratory syndrome virus

“…There is limited in vivo research reported on PPAR pathway and PRRSV infection. However, one in vitro cell culture assay revealed that increased expression of PPAR-γ may be highly involved in the macrophage polarization during PRRSV replication and infection [44]. In addition, two important fatty acid binding proteins (FABPs 4 and 5) are associated with the PPAR pathway and its specific regulatory functions.…”