Cross-Reactions in the Ouchterlony Plate: Analysis of Native and Halogenated Bovine Serum Albumins

Cross-reactions in the Ouchterlony plate were studied by means of native and halogenated bovine serum albumins and several of their antisera. The following observations were made: The comparison of two immunologically related antigens yielded a major cross-reaction for that antigen which possessed a closer affinity to the reference antibody. The degree of cross-reactivity between the antigens was reflected by the length of the spur.When both antigens possessed nearly the same degree of immunologic affinity to the antibody, their precipitate lines would fuse.Identical pairs of cross-reacting antigens yielded different precipitate patterns with different reference antibodies.The formation of separate specific precipitates by cross-reacting antigens in mixtures depended on the relative concentrations of the antigens in the mixture, on the degree of immunologic affinity between these antigens, and on the antibody concentration.The immunologic distinction between related antibodies was much less pronounced than the distinction between the corresponding cross-reacting antigens.Variable precipitate patterns were obtained when cross-reacting antigens were analyzed by means of mixtures of their respective antisera and when immunologically related antisera were analyzed by means of mixtures of their respective antigens. From findings in this and in a preceding paper (9) it was concluded that the basic precipitate patterns described by Ouchterlony do not always indicate immunologic identity, partial identity, or nonidentity; these patterns can be considerably modified by changes in the relative concentrations of the immune systems, by the degree of immunologic affinity between the reagents, by the choice of the reference reagent, and by the degree of immunologic purity of the reference reagent.