Submitted to: Clinical and Vaccine Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2011
Publication Date: 5/1/2011
Citation: Trible, B.R., Kerrigan, M., Crossland, N., Potter, M., Faaberg, K., Hesse, R., Rowland, R.R. 2011. Antibody recognition of porcine circovirus type 2 capsid protein epitopes after vaccination, infection, and disease. Clinical and Vaccine Immunology. 8(5):749-757. Interpretive Summary: In late 2005, sporadic cases of a high mortality disease were observed in growing pigs among swine herds of the United States. Following preliminary investigations, a presumptive diagnosis of postweaning multisystemic wasting syndrome (PMWS) was made based on clinical signs, lesions, and the consistent finding of porcine circovirus type 2 (PCV2) in affected pigs. Although, commercial vaccines are now available for this devastating disease; veterinarians have very little understanding of the mechanism of cross-protection between the vaccine virus and the field virus affecting the pig. This paper describes a study designed to investigate what portions of the virus capsid protein (the protective coating of the virus) that the pig’s immune system responds to and compared these results across 462 recent PCV2 viral isolates from pigs in the United States. Results from this experiment demonstrate a small conserved protein sequence that generates the highest antibody responses in pigs with the most severe forms of PMWS disease in pigs. In summary, this paper suggests that this small portion of the virus may play a critical role in causing severe disease in pigs.
Technical Abstract: Open reading frame 2 (ORF2) of porcine circovirus type 2 (PCV2) codes for the 233-amino-acid capsid protein (CP). Baculovirus-based vaccines that express only ORF2 are protective against clinical disease following experimental challenge or natural infection. The goal of this study was to identify regions in CP preferentially recognized by sera from experimentally infected and vaccinated pigs and to compare these responses to those of pigs diagnosed with porcine circovirus-associated disease (PCVAD), including porcine multisystemic wasting syndrome (PMWS) and porcine dermatitis and nephropathy syndrome (PDNS). The approach was to react porcine sera with CP polypeptide fragments followed by finer mapping studies using overlapping oligopeptides that covered amino acids 141 to 200. The results showed that vaccinated pigs preferentially recognized only the largest polypeptide fragment, CP(43-233). A subset of experimentally infected pigs and pigs with PDNS showed strong reactivity against a CP oligopeptide, 169-STIDYFQPNNKR-180. Alanine scanning identified Y-173, F-174, Q-175, and K-179 as important for antibody recognition. The results from this study support the notion of PCV2 modulation of immunity, including antibody responses that may represent a precursor for disease. The recognition of CP(169-180) and other polypeptides provides opportunities to devise diagnostic tests for monitoring the immunological effectiveness of vaccination.