Development of cell-mediated immunity to porcine circovirus type 2 (PCV2) in caesarean-derived, colostrum-deprived piglets

Abstract

The interaction between porcine circovirus type 2 (PCV2) and the pig immune system has been suggested to be a determinant event for the pathogenesis of postweaning multisystemic wasting syndrome (PMWS). To gain insight into the host immune mechanisms developed upon PCV2 infection, early innate and adaptive immune responses were examined in 1-week-old, caesarean-derived, colostrum-deprived piglets using a subclinical infection model of PCV2 in combination with lipopolysaccharide (LPS) as a potential immunostimulation factor. The use of LPS did not show any significant effect on the course of PCV2 infection, nor did in the evolution of the immunological parameters evaluated. Ex vivo responses were detected as early as 1 day post-infection (PI) and consisted of an elevation of the plasmatic levels of interleukin (IL)-8 in PCV2-inoculated pigs followed by an increase on plasmatic IFN-alpha at day 5 PI. Regarding IL-10, only one PCV2-inoculated pig was positive (day 7 PI); this pig was the only one in which viremia persisted until the end of the study. In vitro cytokine determination showed that, regardless of the treatment administrated to the pigs, an IL-10 release was observed when peripheral blood mononuclear cells (PBMC) cultures were stimulated with PCV2. Seroconvertion to PCV2 measured by an immunoperoxidase monolayer assay (IPMA) occurred between 7 and 14 days PI, whereas neutralizing antibodies (NA) did not appear until day 29 PI. PCV2 DNA was first detected in serum at day 7 PI, reaching the peak of viremia between days 14 and 21 PI, followed by a drop in viral load that was found coincident with the appearance of PCV2-specific IFN-gamma-secreting cells (PCV2-IFN-gamma-SC) and NA. Results from the present work suggest that viral clearance might be mediated by the development of PCV2-IFN-gamma-SC in contribution to the PCV2-specific NA.

A commercial porcine circovirus (PCV) type 2a-based vaccine reduces PCV2d viremia and shedding and prevents PCV2d transmission to naïve pigs under experimental conditions

“…While a detectable antibody response to PCV2 vaccination is a good predictor for successful vaccine administration, it is not necessary to confer protection to pigs. It has been demonstrated that pigs with no detectable humoral response after PCV2 vaccination were protected from subsequent challenge likely due to induction of cellular immunity [35], [36]. While in this study 4/9 VAC + CHAL pigs had detectable antibody titers at challenge, 8/9 VAC + CHAL were protected from subsequent PCV2d challenge and had significantly reduced PCV2d viremia and PCV2d nasal and fecal shedding compared to CHAL pigs indicating that Circovac® confers protection against PCV2d.…”

Assessment of neutralizing and non-neutralizing antibody responses against Porcine circovirus 2 in vaccinated and non-vaccinated farmed pigs

“…As protection from PCVAD is induced by PCV2 vaccination (Beach & Meng, 2012;Kristensen et al, 2011;Martelli et al, 2011), it is plausible that, under field conditions, PCV2-specific T-cell immunity is most likely an essential and substantial component of protection from PCVAD. This conclusion is supported by results obtained in other studies (Fort et al, 2009b;Martelli et al, 2011). PCV2 neutralizing antibody titres were significantly different between animals of different aged but identical vaccination groups (P,0.05).…”

One dose of a porcine circovirus 2 subunit vaccine induces humoral and cell-mediated immunity and protects against porcine circovirus-associated disease under field conditions

“…proteins. The intensity of the generated response differs using either the Cap protein or the whole 516 PCV as an in vitro stimulus; IFN-γ responses obtained by stimulating PBMC with the whole virus 517 are higher than with the Cap protein, suggesting that infected animals in which PCV2 is replicating 518 might respond strongly to other viral components different from the Cap protein (Fort et al, 2009b). 519…”