#10-012

Complete

Date Full Report Received

09/30/2011

Date Abstract Report Received

09/30/2011

Investigation

Institution:
Primary Investigator:

This project was intended to determine whether or not pig with PCVAD had T lymphocytes that responded to different epitopes of the PCV CP, when compared with vaccinated pigs or pigs that had been infected with PCV2 alone. The PCVAD model used was the dual-infection model with PRRSv and PCV2 as the pathogens. Work from Dr. Rowland’s lab had shown that serum antibodies from infected pigs identified a region of the coat protein (CP) that was less readily recognized by antibodies from vaccinated pigs, and our previous studies had shown that PCV2 vaccinated pigs had T cells that recognized a specific pattern of epitopes from CP. Because there were differences in antibody epitopes, we reasoned that differences would also exist in T cell epitopes. Therefore, we hypothesized that infected pigs would recognize a different array of peptides from CP compared with vaccinated pigs, and that dual-infected (PCVAD) pig T cell epitopes would differ from those of PCV2-infected pigs. Experiments were performed using sets of 4 pigs, each one either either:1) untreated, 2) vaccinated with a commercially available vaccine, 3) infected with PCV2, or 4) infected with PCV2 and PRRSv. Blood was collected for serum at intervals throughout the experimental period, and PRRSv and PCV2 antibodies were evaluated. During active infection, CP polypeptide ELISA assays were run to evaluate antibody binding to either the full-length or truncated CP peptide. At necropsy, lymph nodes were taken for histology, and single cell suspensions were prepared for immunophenotyping by flow cytometry, and T cell proliferation and Interferon-gamma ELISPOT assays to detect responses to individual chemically synthesized CP 30-mer peptides. The T cell epitope results showed that different patterns of epitope recognition occurred among vaccinated, PCV2-infected and dual-infected pigs, with vaccinated pig responses resembling our previous study, PCV2 infected pig T cells recognizing primarily 2 peptides at the amino terminus of the protein, and dual-infected pig T cells primarily recognizing 5 peptides at the carboxy terminus of the CP protein. These data were consistent with our hypothesis. Additional support was obtained from the antibody assays, lymphoid cell measurements, immunophenotyping and histological examinations. These findings confirm that PCV2- and dual-infected pigs have T cells that respond to fewer peptides compared with vaccinated pigs and that the epitopes recognized by PCV2-infected pig T cells are in a different location on the protein compared with dual-infected pig T cells. These findings suggest that PCVAD represents an inability of the pig immune system to adequately control the virus, perhaps as a result of co-infection with PRRSv. Thus, prevention of infection by PRRSv likely represents an important control strategy for PCVAD.