Outbred mice as an appropriate model for evaluating the immunogenicity of vaccines against porcine circovirus 2.

Abstract

Background: Porcine circovirus type 2 (PCV2) is the causative agent of porcine circovirus-associated diseases, leading to substantial economic losses in global swine production. Although various commercial vaccines exist, an appropriate and translational animal model is essential for evaluating vaccine-induced immune responses. Inbred mouse strains are traditionally preferred due to their genetic uniformity; however, outbred animals may reflect a broader immunological variability than the natural target species. The number of comparative studies assessing outbred mice for PCV2 vaccine immunogenicity remains limited.

Aim: This study aimed to determine whether outbred mice represent an appropriate model for assessing the immunogenicity of PCV2 vaccines by comparing them with two commonly used inbred strains, C57BL/6 and BALB/c.

Methods: A total of 108 6-week-old female mice from three genetic backgrounds (Swiss, C57BL/6, and BALB/c) were immunized with recombinant PCV2a- or PCV2b-based vaccines or inoculated with water for injection as controls. Vaccinations were administered on days 0 and 14, and blood samples were collected on days 0 and 28. Humoral immune responses were assessed using an in-house enzyme-linked immunosorbent assay to determine seroconversion rates and end point antibody titers. Statistical analysis was performed using one-way analysis of variance, with a significance threshold of p < 0.05.

Results: All vaccinated animals were seroconverted at 28 days post-vaccination, whereas the control groups remained negative. High antibody titers, ranging from 1:25,600 to 1:102,400, were observed in all immunized groups, ranging from 1:25,600 to 1:102,400 depending on strain and vaccine genotype. No statistically significant differences were detected among the vaccinated groups (p = 0.0631), indicating that the humoral immune responses of Swiss outbred mice were comparable to those of the inbred strains.

Conclusion: Outbred Swiss mice exhibited robust antibody responses equivalent to those of C57BL/6 and BALB/c mice following immunization with the PCV2a and PCV2b vaccines. These findings support the suitability of Swiss mice for assessing total IgG humoral responses in immunogenicity studies and PCV2 vaccine quality-control assays.