[Development of a method for the quantitative determination of the immunizing antigen (140S) of the foot-and-mouth disease virus].

Attempts were made to work out a method for measuring the amount of the 140 S antigen in virus suspensions. Early postinfection sera were obtained from guinea pigs against the productional strains of the foot-and-mouth disease virus which were used in the radial immunodiffusion test. The investigated virus suspensions were concentrated 50 to 200 times and were placed in a CsCl gradient for gradient centrifugation. The 140 S antigen fractions obtained were titrated in a radial immunodiffusion test. The size of the resulting precipitation circles were defined for the individual dilutions of the antigen, and the method of least squares was employed to establish the standard straight lines for each of the investigated productional strains of the FMD virus. The new method makes it possible to fix the content of the 140 S antigen in productional series of the FMD virus intended for vaccine production.