Porcine reproductive and respiratory syndrome (PRRS) is a highly contagious and lethal disease in the global swine industry. The major target cells of PRRS virus (PRRSV) are porcine alveolar macrophages (PAMs). With the aim to elucidate the pathogenic mechanism of PRRS and thus to help prevention and control of the disease, we investigated the functional changes of PAMs caused by PRRSV infection. PAMs from fifteen 35-day-old piglets that were free of PRRSV and porcine circovirus type 2 (PCV2)

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... tibody and antigen, were cultured in vitro and divided into 4 groups, i.e., control group, PRRSV group, myeloid differentiation 88 (MyD88) interference group (interference group), and MyD88 interference-PRRSV infection group (interference-PRRSV group). The PRRSV-infected cells was observed using confocal scanning laser microscope; the MyD88 gene of PAMs was knocked down by siRNA; the transcription of Toll-like receptors (TLRs) in PAMs was detected by fluorescent quantitative real-time PCR; the protein concentrations of IL-1β, IL-6, IL-10 and TNF-α in the culture supernatant were detected by ELISA; the protein concentrations of MyD88, NF-κB and phosphorylated IкB (p-IκB) in cytoplasm and NF-κB in nucleus were detected by western blot; and the NF-κB-DNA binding activity in nucleus was detected using EMSA. The results showed PRRSV infection led to the increase in the TLRs mRNA and protein concentrations of IL-1β, IL-6, IL-10 and TNF-α in PAMs and derived supernatants. After PRRSV infection, the protein concentrations of MyD88 and p-IκB in cytoplasm and NF-κB in nucleus were higher than those in the control group. In addition, the protein concentrations of MyD88 and p-IκB in cytoplasm and NF-κB in nucleus and the NF-κB-DNA binding activity in the former group were significantly lower than those in the latter one. In conclusion, PRRSV could up-regulate the protein expression of IL-1β, IL-6, IL-10 and TNF-α in PAMs through TLRs-MyD88-NF-κB signaling pathway.