Protective immunity in swine induced by Porcine Circovirus 2b inactivated vaccines with different antigen payload

• Published in: Veterinary microbiology 2021-01, Vol.252, p.108887-108887, Article 108887
• Main Authors: Guarneri, Flavia, Tresoldi, Enrico Tommaso, Sarli, Giuseppe, Boniotti, Maria Beatrice, Lelli, Davide, Barbieri, Ilaria, Bacci, Barbara, D’Annunzio, Giulia, Amadori, Massimo
• Format: Article
• Language: English
• Subjects: Antibody response; Antigens; Enzyme-linked immunosorbent assay; Giant cells; Hogs; Ileum; Immunity; Immunohistochemistry; Lymphoid tissue; Pig; Porcine circovirus 2; Potency; Protection; Vaccine; Vaccines; Viremia; γ-Interferon
• ISSN: 0378-1135; 1873-2542
• DOI: 10.1016/j.vetmic.2020.108887

•The PCV2-specific, IFN-gamma release assay is a valid tool for assessing the efficacy of whole virion PCV2b vaccines.•The PCV2b-specific, IFN-gamma response is stimulated by vaccination, and not by infection.•Mean antibody titers and T cell responses to PCV2b vaccines are proportional to antigen doses. Porcine Circovirus 2 (PCV2) vaccines are poorly standardized in terms of antigen payload and correlates of protection. Therefore, twenty, 45-day old piglets were divided into four groups of 5 animals each and vaccinated with 800 / 266 / 88 / 0 nanograms, respectively, of an inactivated PCV2b strain formulated in the same oil adjuvant. Twenty-six days later, all the pigs were challenged intranasally with the homologous PCV2b strain. No clinical signs were observed in the pigs under study. Viremia was observed after challenge in all the control pigs, as well as in 3 pigs of the 266 and 88-ng groups (one and two, respectively). No pigs of the 800-ng group developed viremia. On the basis of post challenge viremia, the PCV2b vaccine under study had a titer of 11 Protective Doses (PD) 50 %, and 1 PD50 amounted to 74 ng of PCV2b Ag. Neutralizing and ELISA Ab titers showed no obvious correlation with protection in the single animals, even though the 800-ng group developed a significantly higher mean Ab response. All the pigs with a PCV2-specific, IFN-gamma response at 3 weeks after vaccination in whole blood samples were protected against viremia. In lymphoid tissues (mainly tonsils and ileum) the presence of sparse reactive histiocytes and multinucleated giant cells was the only PCV2-associated feature and, by immunohistochemistry, only 3 out of 20 subjects showed a low viral load.