Immunochemical Studies of Foot and Mouth Disease

Abstract

The three known antigenic components demonstrable in foot and mouth disease infectious tissue culture fluids were isolated and examined for complement-fixing activity. Antisera containing antibody to the three antigens titered higher against the 140 S virus particles than with the 12 S protein subunit or infection-associated antigens. The difference in serum titers with the three antigens was more evident using a fixation period of 1 ½ hr at 37°C than one of 20 hr at 4°C. Advantage was taken of this fact to develop a quantitative assay for 140 S antigen. It was found that 0.231 ± 0.035 µg/ml of 140 S antigen fixed 4 of 5 50% hemolytic units of complement with a selected antiserum dilution using a fixation period of 1 ½ hr at 37°C.Assay for the infection-associated antigen could be performed with heterologous antisera in view of the non-type specificity of this antigen. An assay for 12 S antigen in mixed antigen preparations could not be made. However, an assay with the isolated 12 S component indicated 0.039 µg/ml provided the end point using a fixation period of 20 hr at 4°C.The implications of the findings with respect to antibody titrations and diagnostic virus typing were discussed. The limitations of the complement-fixation technique as applied to foot and mouth disease were presented and the necessity of preparing specific antisera indicated.