Enhancing Capsid Stability of a Foot-and-Mouth Disease Virus Vaccine Strain Through VP1-Directed Chimeric Design While Preserving Antigenicity

Figures

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  Figure 1. Schematic representation of the recombinant (R) O1 M–O JC_VP1 virus. The VP1 coding region of the O1 Manisa (O1 M) strain was replaced with the corresponding sequence from the O Jincheon (O JC) strain, while all other genomic regions were retained from the O1 M backbone. The substituted VP1 region is highlighted in green.

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  Figure 2. Morphological analysis of purified FMDV particles. Purified O JC wild-type and (R) O1 M–O JC_VP1 viruses were negatively stained with 1% uranyl acetate and visualized by transmission electron microscopy (TEM). The scale bar indicates 50 nm.

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  Figure 3. Comparative evaluation of the physical stability of O JC wild-type and (R) O1 M-O JC_VP1 viruses. (a) Thermal stability was evaluated by a particle stability thermal release assay (PaSTRy) using the RNA-binding dye SYBR Green II; the first derivative of fluorescence is shown, and melting temperatures (Tm, °C) are summarized in the table. (b–d) The stability of purified 146S antigens was further determined by quantifying 146S content by high-performance liquid chromatography and presenting the results as relative values after (b) incubation at 25 °C or 45 °C for 30 min, (c) chloroform treatment (purified virus: chloroform = 1:1, v/v) for 5 min, and (d) storage in PBS at 4 °C for 0, 5, 15, and 25 days. n.d, not detected.

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  Figure 4. Immunogenicity evaluation of O JC wild-type and (R) O1 M–O JC_VP1 vaccines in pigs. (a) Study design and sampling schedule. Eight-week-old pigs were immunized (day 0) and boosted (day 28) with O JC wild-type (Group 1, n = 6) or (R) O1 M–O JC_VP1 (Group 2, n = 6) vaccines; blood was collected at the indicated time points. (b) Serological responses measured by FMDV structural protein (SP) O ELISA and expressed as percent inhibition (PI, %). A PI value of ≥50% (dotted line) was considered to indicate a positive result. (c) The homologous virus-neutralizing (VN) antibody titers were measured using the virus neutralization test. A titer ≥ 1:45 (1.65 log10) (dotted line) was considered to indicate a positive result. ns, not significant. Bars represent mean values.