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

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.

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.

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.

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.

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.