Abstract
The study was conducted to evaluate whether avian β-defensins (AvBDs) could be induced by Newcastle disease virus (NDV) infection, and to investigate the potential signaling pathway of AvBD2 induction in response to NDV infection as well. First, mRNA expression of AvBDs (1–14) was evaluated in the chicken embryo fibroblasts (CEFs) infected with NDV strain F48E9 at 6, 12, 24, 36, and 48 h post-inoculation (hpi), respectively. The results demonstrated a significant induction of AvBD2 in CEFs elicited by the NDV strain. Then, we expressed and purified the AvBD2 proteins in both eukaryotic cells and prokaryotic cells. Of the two recombinant AvBD2 proteins, only the protein expressed in eukaryotic cells showed directly antiviral activity against NDV strain F48E9 in vitro. Ligands of toll-like receptors (TLRs) were chosen as alternatives to NDV to further study signaling pathway of AvBD2 induction here, due to insufficient upregulation of AvBD2 expression elicited by NDV. We found that the mRNA expression of AvBD2 was highly upregulated by Pam3CSK4, FLA-ST, and ODN-M362. Then, four inhibitors of signaling pathway, including inhibitors of JNK, ERK1/2, p38 MAPK, and NF-κB, were used in this study. Of the four inhibitors, only inhibition of the p38 MAPK signaling pathway significantly reduced AvBD2 expression after stimulation with Pam3CSK4, FLA-ST and ODN-M362, respectively. Taken together, these results revealed that AvBD2 play a pivotal role in host innate immunity response to NDV infection. The mRNA expression of AvBD2 might be regulated in a p38 MAPK-dependent manner.
Highlights
Newcastle disease virus (NDV), known as avian paramyxovirus type 1, belongs to the genus Avulavirus in the family paramyxoviridae (Mayo, 2002) and is the etiological agent of Newcastle disease (ND), which is an important disease hazardous to the poultry industry
The chicken embryo fibroblasts (CEFs) were infected with NDV strain F48E9 at different multiplicity of infection (MOI) (0.01, 0.1, 1, 10, and 100)
The results showed that the survival rate of cells was significantly increased in treatments of 1–100 MOI of NDV infection at 24 hpi, compared to the other treatments (p < 0.05) (Figure 1A)
Summary
Newcastle disease virus (NDV), known as avian paramyxovirus type 1, belongs to the genus Avulavirus in the family paramyxoviridae (Mayo, 2002) and is the etiological agent of Newcastle disease (ND), which is an important disease hazardous to the poultry industry. Numerous studies have focused on characterizing the pathogenesis of different NDV isolates in past years, while few studies have been done to evaluate host response to NDV infection. Our recent study demonstrated that NDV infection induces strong innate immune responses and intense inflammatory responses at early stage in goose (Xu et al, 2016). It has been reported that pigeon paramyxovirus type 1, a variant of NDV, induces immune responses characterized by activation of TLRs (TLR3 and TLR7), iNOS, and avian β-defensin (AvBD) 2 and 10 of pigeons post infection (Li et al, 2015)
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