Innate immune defenses induced by CpG do not promote vaccine-induced protection against foot-and-mouth disease virus in pigs.

Emergency vaccination as part of the control strategies against foot-and-mouth disease virus (FMDV) has the potential to limit virus spread and reduce large-scale culling. To reduce the time between vaccination and the onset of immunity, immunostimulatory CpG was tested for its capacity to promote early protection against FMDV challenge in pigs. To this end, CpG 2142, an efficient inducer of alpha interferon, was injected intramuscularly. Increased transcription of Mx1, OAS, and IRF-7 was identified as a sensitive measurement of CpG-induced innate immunity, with increased levels detectable to at least 4 days after injection of CpG formulated with Emulsigen. Despite this, CpG combined with an FMD vaccine did not promote protection. Pigs vaccinated 2 days before challenge had disease development, which was at least as acute as that of unvaccinated controls. All pigs vaccinated 7 days before challenge were protected without a noticeable effect of CpG. In summary, our results demonstrate the caution required when translating findings from mouse models to natural hosts of FMDV.

Toll-like receptor 7 and MyD88 knockdown by lentivirus-mediated RNA interference to porcine dendritic cell subsets.

Sensing of viruses by dendritic cell (DC) pathogen recognition receptors (PRRs) represents a critical event during innate antiviral immune responses. Identification of these PRRs has often posed a problem due to difficulties in performing gene function studies in the naturally targeted hosts. Consequently, we developed a lentivirus (LV)-based strategy for specific gene knockdown in porcine DC. Short hairpin RNAs (shRNAs) were designed, targeting toll-like receptor 7 (TLR7) and the adaptor protein MyD88. As cellular targets, monocyte-derived DC (MoDC) and Flt3 ligand-induced DC (Flt3L-DC), DC precursors including monocytes and haematopoietic stem cells (HSCs) as well as plasmacytoid DCs (pDCs) were employed. Transduction efficiencies ranged from 40 to 95%. The LV-mediated shRNA delivery was functionally active, reducing TLR7 and MyD88 mRNA in MoDC and conventional Flt3L-DC, and blunting the responsiveness to TLR7 ligands in Flt3L-DC. Although infection of MoDC by the LV did neither influence MHC class II and CD80/86 expressions, nor cytokine responses, the infection of Flt3L-DC induced a phenotypic maturation. Furthermore, the interaction of the LV with pDC induced high levels of interferon-alpha. Taken together, these studies characterize the interaction of the LV with different DC subsets and demonstrate the suitability of LV-mediated small interfering RNA delivery for targeting PRR knockout for MoDC and conventional Flt3L-DC.