M1 polarization of chicken macrophage HD11 can be activated by duck Tembusu virus via MyD88-NF-κB-mediated signaling pathway.

Duck Tembusu virus (DTMUV) has caused significant economic losses to the global duck industry since its outbreak in 2010. The macrophages act as the key immune cell, and its polarization in different functional states is very important for host's immune responses and microbial infections. Avian macrophages are the main target cells of DTMUV, its polarization induced by DTMUV and the underlying mechanisms were explored in this study. Through quantitative real-time PCR, nitrite assay, and flow cytometry analysis, we found that DTMUV caused severe inflammatory responses in chicken macrophage line HD11 by reprogramming the expression of M1- and M2-associated genes, leading to the polarization of HD11 macrophage to M1-type. In term of mechanism, transcriptomics was performed to analyze the M1-type polarization triggered by DTMUV, it was found that most differential genes were implicated in biological processes, and DTMUV infection significantly activated innate immune signaling pathways, including cytokine-cytokine receptor interaction, MAPK signaling pathway. Moreover, transcription factors NF-κB and AP1 also be activated after viral infection. However, further validation analysis by inhibitors and siRNAs of NF-κB and AP1 showed that NF-κB molecule was essential for DTMUV-induced M1 polarization in HD11 cell, but not AP1. Additionally, the inhibiting assays targeting MyD88 and TRIF molecules were conducted to determine their effect on NF-κB and M1-associated genes upregulated by DTMUV. The results showed that although the inhibition of both MyD88 and TRIF significantly downregulated the mRNA level of NF-κB, but the expression of M1-associated genes such as CD86 was lower in MyD88 inhibition group than in the other group, indicating that the role of MyD88 in mediating M1 polarization induced by DTMUV was more important. Overall, these results demonstrated that DTMUV infection induces M1-type polarization in chicken macrophage HD11 through MyD88-NF-κB signaling pathways. This finding will lay the foundation for further study the pathogenesis of DTMUV, and provide new insights into the prevention and control of this disease.