Evaluation of Antibodies Induced by the Injection of Single Capsid Protein or Purified Virus Particle of Coxsackievirus B3 in Mice

Four capsid proteins (VP1, VP2, VP3, and VP4) of coxsackievirus B3 (CVB3) were expressed as recombinant proteins in an Escherichia coli expression system and used as antigens for subunit vaccines against CVB3 in ICR mice. Antigens were expressed as thioredoxin-histidine (TrxHis)-tagged protein and purified before immunization. Although all VPs other than VP4 induced anti-CVB3 specific antibodies in mice (detected by ELISA and western blotting), they did not neutralize the infectious CVB3 in a virus neutralization assay. Meanwhile, 2 virus strains were purified from CVB3 virus stock on the basis of their plaque size on HeLa cells. ICR mice were infected with the 2 purified virus strains (S-strain and L-strain) and unpurified virus stock (wild type) to analyze the difference in antibody responses against infections of purified and unpurified virus strains. The reactivity of antisera against each virus strain was tested by ELISA, and the results showed that the inoculation of purified virus strain induced a strong antibody response against the inoculated strain. As a result, the antibody response against wild-type and other virus strains was suppressed. These results suggest using unpurified virus stock as an antigen is advantageous for inducing a broad antibody response in inoculated animals.