The objective of the present study was to characterize and compare the differences in gene expression associated with innate immune response of blood monocytes (Mos) between healthy subclinically PCV2-infected and PCV2-free pigs prior to and after lipopolysaccharide (LPS) stimulation in vitro by relative quantitative real-time PCR (q-rt-PCR). Genes coding for 24 innate molecules, including toll-like receptors (TLRs), interferon-regulatory factors (IRFs), nuclear factor kappa-light chain-enhancer of activated B cells (NF-κB) and pro-inflammatory cytokines were evaluated. When compared with PCV2-free pigs, Mos from subclinically PCV2-infected pigs showed significantly lower mRNA expression levels in TLR-9, IRF-3, IRF-6, IRF-7, IL-6, IL-12p35, IL-12p40 and IFN-α under no further stimulation. Following LPS stimulation in vitro, a broad and/or obvious reduction in TLRs, IRFs, IL-12 and IFN-α along with increase in IL-1α, IL-6, IL-8, IL-10 and/or TNF-α were seen in both PCV2-free and subclinically PCV2-infected pigs; when compared with PCV2-free pigs, the subclinically PCV2-infected pigs had significantly higher expression levels in TLR-10 and IRF-1 but lower expression levels in IRF-6, IL-1α and IL-12p40. On the contrary, the expression level of NF-κB was consistently higher in subclinically PCV2-infected pigs than in PCV2-free pigs with or without LPS stimulation. The changes seen in the present study suggest that the subclinically PCV2-infected pigs may look healthy clinically, but their innate immunity has become dis-regulated or is in an improper status. The adverse condition may become even worse when exposed to certain bacterial products such as endotoxin. Such alterations in the innate immune system may make the subclinically PCV2-infected pigs more vulnerable to the secondary infection and subsequent PCV2-associated disease development.
Active Infection of Human Blood Monocytes by Chikungunya Virus Triggers an Innate Immune Response
