Relationship of the Antigenic Structure of Foot-and-Mouth Disease Virus to the Process of Infection

SUMMARY Two distinct immunogenic sites were present on the surface of foot-and-mouth disease virus. One site was concerned with adsorption of the virus to susceptible cells as well as the production of neutralizing antibody. Removal of this site with trypsin did not alter the gross morphology but the particles then had reduced infectivity, although the virus RNA was present in a fully infective form. The presence of a second immunogenic site was shown by the fact that trypsin-treated particles also produced a neutralizing antibody. This differed from the neutralizing antibody against the intact virus in that it was absorbed by trypsin-treated particles. Some of the neutralizing activity of antiserum produced by inoculation of intact virus particles was also absorbed by trypsin-treated particles. The relative activities of the two antibody-producing sites varied with different strains of virus.