Porcine circovirus type 2 increases interleukin-1beta and interleukin-10 production via the MyD88–NF-kappa B signaling pathway in porcine alveolar macrophages in vitro

Porcine alveolar macrophages (PAMs) represent the first line of defense in the porcine lung after infection with porcine circovirus type 2 (PCV2) via the respiratory tract. However, PCV2 infection impairs the microbicidal capability of PAMs and alters cytokine production and/or secretion. At present, the reason for the imbalance of cytokines has not been fully elucidated, and the regulatory mechanisms involved are unclear. In this study, we investigated the expression levels and regulation of interleukin-1beta (IL-1β) and IL-10 in PAMs following incubation with PCV2 in vitro. Levels of IL-1β and IL-10 increased in PAM supernatants, and the distribution of nuclear factor kappa B (NF-κB) p65 staining in nucleus, expression of MyD88 and p-IκB in cytoplasm, and DNA-binding activity of NF-κB increased after incubation with PCV2, while p65 expression in PAM cytoplasm decreased. However, when PAMs were co-incubated with PCV2 and small interfering RNA targeting MyD88, those effects were reversed. Additionally, mRNA expression levels of Toll-like receptors (TLR)-2, -3, -4, -7, -8, and -9 increased when PAMs were incubated with PCV2. These results show that PCV2 induces increased IL-1β and IL-10 production in PAMs, and these changes in expression are related to the TLR–MyD88–NF-κB signaling pathway.