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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 mμ infective component (D-fraction) combines homotypically with antibody. Thermal degradation of the 25 mμ component produces a smaller component of enhanced activity which combines heterotypically with antibody and resembles the naturally occurring 7 mμ component (U-fraction). The influence of heating upon the 7 mμ component is marked by a sharpened specificity. The specificity and activity of unfractionated starting materials may be interpreted in terms of those of the 25 and 7 mμ components present in the separable fractions. Significant differences between the reactions observed in the long and short incubation procedures emphasize the advantages of the latter in specificity studies. The composition and treatment of the initial antigens and the test procedures employed must be carefully defined in such studies of antigen-antibody combination.
Bradish et al. (1960) studied this question.