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SUMMARY: The antibody combining properties of the U- and D-fractions of the virus system of foot-and-mouth disease were investigated by complement-fixation methods. The virus fractions were titrated in antibody excess and used as excess antigens in titrations of antisera. The results demonstrate that the complement-fixing activity in antibody excess increased with time of incubation by a threefold or higher factor when the U-fraction was used as antigen than when the D-fraction was used. Titrations of antisera showed that distinct combining activities were involved according to the virus fraction used as antigen in excess. Data in support of this were obtained in adsorption experiments in the absence of complement by titration of the residual antibody activity following sedimentation of the complexes formed with the U- or D-fractions. The reaction in the region of equivalence, in which neither antigen nor antibody is in effective excess, was investigated. A rapid and objective procedure for the treatment of complement-fixation data is presented.
Bradish et al. (1960) studied this question.