Nature of the antibody response to the foot-and-mouth disease virus particle, its 12S protein subunit and the isolated immunizing polypeptide VP1.

Inoculation of inactivated 146S foot-and-mouth disease virus particles into guinea-pigs elicited the formation of neutralizing antibody and the serum had a 10-fold higher titre in radioimmunoassay (RIA) with 146S particles than with the 12S virus subunit. In contrast, a single inoculation of the 12S subunit or the isolated polypeptide VP1 elicited the formation of antibody having a much lower titre in RIA with the 146S particle than with the 12S subunit and low or undetectable neutralizing activity. However, sera from guinea-pigs given two or more inoculations of the 12S subunit or VP1 had neutralizing activity. The level in the anti-VP1 serum was lower than that in the anti-12S serum and both were much lower than that in animals receiving two inoculations of the 146S particle. The neutralizing activity elicited by the three antigens was absorbed by the homologous antigen. In contrast, neither the 12S subunit nor VP1 absorbed the anti-146S neutralizing antibody and VP1 did not absorb the anti-12S subunit neutralizing antibody. However, the 12S subunit partly absorbed the neutralizing activity elicited by VP1. The results are compatible with a model in which the 146S particle elicits a spectrum of neutralizing antibodies which are completely absorbed by the homologous particle but only partially by the 12S subunit or VP1. The results are discussed in relation to the structural features required for the production of neutralizing antibody.