Complement-fixation Studies of the Specificity of the Interactions between Components of the Virus System of Foot-and-Mouth Disease and its Antibodies

SUMMARY: The type and subtype specificities of the interactions between fractions of the virus system of foot-and-mouth disease and its antibodies were investigated by complement-fixation methods. Specificity is discussed in terms of a cross-fixation ratio. The 25 mp infective component (D-fraction) combines homotypically with antibody. Thermal degradation of the 25 mp component produces a smaller com-ponent of enhanced activity which combines heterotypically with antibody and resembles the naturally occurring 7 mp component (U-fraction). The influence of heating upon the 7 mp component is marked by a sharpened specificity. The specifi-city and activity of unfractionated starting materials may be interpreted in terms of those of the 25 and 7 mp components present in the separable fractions. Signifi-cant differences between the reactions observed in the long and short incubation procedures emphasize the advantages of the latter in specificity studies. The com-position and treatment of the initial antigens and the test procedures employed must be carefully defined in such studies of antigen-antibody combination. As in other systems of multiple antigens and antibodies, viral antigen