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


RESULTS
All 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-gamma 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-gamma 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-gamma 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-gamma positive CD8hi cytotoxic T cells as well as IFN-gamma positive CD8-/low helper T cells after PCV2 in vitro re-stimulation.


CONCLUSIONS
Infection 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.
Steiner
Esther
E
Institute of Virology and Immunoprophylaxis, Mittelhäusern, Switzerland. esther.steiner@tki.unibe.ch
Balmelli
Carole
C
Gerber
Heidi
H
Summerfield
Artur
A
McCullough
Kenneth
K
D000818:Animals; D000914:Antibodies, Viral / Q000276:immunology; D018173:Circoviridae Infections / Q000276:immunology / Q000662:veterinary*; D017925:Circovirus / Q000276:immunology*; D007111:Immunity, Cellular; D007371:Interferon-gamma / Q000096:biosynthesis; D007958:Leukocyte Count; D018655:Lymphocyte Count; D013552:Swine / Q000276:immunology / Q000821:virology; D013553:Swine Diseases / Q000276:immunology / Q000821:virology*; D013601:T-Lymphocytes / Q000276:immunology; D014766:Viremia / Q000276:immunology / Q000662:veterinary / Q000821:virology
D000914:Antibodies, Viral; D007371:Interferon-gamma