Cellular adaptive immune response against porcine circovirus type 2 in subclinically infected pigs

Abstract

BackgroundPorcine circovirus type 2 (PCV2) is a dominant causative agent of postweaning multisystemic wasting syndrome (PMWS), a multifactorial disease complex with putative immunosuppressive characteristics. Little is known about adaptive PCV2-specific immune responses in infected pigs. Therefore, the T and B cell responses following PCV2 infection in 3-week old SPF piglets infected with PCV2 or PCV2 plus porcine parvovirus (PPV) were studied.ResultsAll animals were asymptomatically infected. At 7 days post infection (d p.i.), B lymphocyte and T lymphocyte numbers decreased in the dual infected, but not in the single infected piglets. At this time point a transient PCV2 viraemia was noted in the PCV2 infected groups. Antibodies against the infecting virus were detectable at day 24-28 p.i. for anti-PCV2 antibodies and at day 10 p.i. for anti-PPV antibodies, with no apparent influence of PCV2 on the early PPV antibody development. In the animals infected with PPV alone, IFN-γ secreting cells (SC) that were not specific for PCV2 were detected by ELISPOT assay at day 7 p.i. Interestingly, this response was absent in the PCV2/PPV dual infected animals. PCV2-specific IFN-γ SC were observed in the PCV2/PPV infected group at 7 d p.i. and in the PCV2 single infected group at 21 d p.i. A reduction in the numbers of IFN-γ SC was observed following anti-CD4 and anti-CD8 antibody treatment, suggesting roles for both CD4+ and CD8+ T cells in the response against PCV2 infection. This was supported by an observed increase in the percentage of IFN-γ positive CD8hi cytotoxic T cells as well as IFN-γ positive CD8-/low helper T cells after PCV2 in vitro re-stimulation.ConclusionsInfection of weaned SPF piglets with PCV2 alone or combined with PPV does not induce disease and in both cases a relatively slow anti-PCV2 antibody response and weak T lymphocyte responses were found. Knowledge on such immunological characteristics is important for both PCV2 pathogenesis and vaccination.

The comparative profile of lymphoid cells and the T and B cell spectratype of germ-free piglets infected with viruses SIV, PRRSV or PCV2

“…Infection with PCV2 caused a decrease in total white blood cells that was associated with a decrease in lymphocytes (Additional file 3). This also agrees with observations of others [17,21].…”

“…While symptoms of PMWS in our piglets were rare, the prevalence of CTL was striking and is consistent with reports by others [18,21]. An exceptionally high proportion of CTL with MHC-II + phenotype was found in all organs.…”

“…T regulatory cells would not be expected to cause lymphopenia, which is supported by the general wellness of our infected GF piglets. However, immunosuppression may compromise protective immune responses to secondary pathogens, known to be a feature of porcine circovirus-associated diseases [14,21].…”

“…However, the response of T cells is generally weak [21]. Although the appearance of specific antibodies is delayed [16,21], subclinical PCV2 infection is characterized by the presence of neutralizing antibodies that correlate with protection from PCV2 infection [20].…”

Sensitive detection of Porcine circovirus-2 by droplet digital polymerase chain reaction

“…1 PMWS has been reported to increase the mortality of pigs by 2-30%. 13 Accurate and rapid detection of PCV-2 could serve to control its spread and reduce economic losses in the pig industry.…”