Immune responses to ORF2-based vaccination and experimental porcine circovirus type 3 challenge in cesarean-derived, colostrum-deprived pigs 2309059

Abstract Introduction PCV3 is a pathogenic member of the family Circoviridae infecting pigs. PCV3-associated disease has been linked to reproductive failure, wasting syndromes, and multisystemic inflammation, although subclinical infections are often reported. Despite global detection, limited experimental studies have hindered comprehensive characterization of PCV3 pathogenesis and host immune responses. Methods Eight-week-old CDCD pigs were intramuscularly vaccinated and boosted with 150 µg of recombinant PCV3 ORF2 protein formulated with 18% (v/v) Emulsigen D and subsequently challenged with 133.33 µg PCV3 via intramuscular (IM) or intranasal (IN) routes. Treatment groups (n = 6/group) included vaccinated or sham-vaccinated pigs subjected to homologous sham or PCV3 challenge by either route. Serum, oral fluids, fecal (FS) and nasal swabs (NS), and PBMCs were collected longitudinally and analyzed by RT-qPCR, ELISA, and flow cytometry. Results No clinical signs were observed throughout the study. Inoculation route and vaccination status significantly influenced the temporal dynamics of PCV3 viremia and viral shedding. IM challenge resulted in earlier, higher viral loads compared with IN challenge, which showed a gradual increase over time. Vaccination prevented viral shedding in FS and NS but only delayed and reduced viremia. Vaccinated pigs developed PCV3-specific IgG prior to challenge, with higher post-challenge levels observed following IN exposure. In contrast, sham-vaccinated challenged pigs exhibited impaired humoral responses. Immune cell profiling revealed a robust early IFN-γ response that was attenuated in vaccinated groups and followed by an increase in regulatory T cells. Conclusion Subclinical PCV3 infection was associated with prolonged viremia. Characterization of a prototype ORF2-based vaccine demonstrated enhanced IgG response, modulation of inflammatory cytokine responses, and prevention of viral shedding, providing insight into PCV3 immunobiology and informing future vaccine development strategies. Funding Source n/a Topic Categories Veterinary and Comparative Immunology (VET)