In double radial diffusion, what indicates that the antigens are NOT identical?

In double radial diffusion, the presence of lines of intersection between antigen-antibody complexes indicates that the antigens are not identical. This occurs when two different antigens are diffusing through a gel and react with a specific antibody, leading to precipitation lines. If the antigens were identical, the precipitation lines would not intersect, as the interaction would produce a single band or zone of equivalence indicating a clear and direct relationship between the antigens and antibodies.

The presence of lines of intersection suggests that different epitopes or structures on the two antigens are being recognized by the same antibody, leading to a separate reaction for each antigen. This differentiation is crucial in immunological studies, as it helps identify variations in antigen integrity and specificity.

The other choices represent different phenomena in the context of double radial diffusion. A zone of equivalence describes a condition where adequate proportions of antigen and antibody result in a distinct precipitate, and double bands reflect multiple responses, but neither directly signifies dissimilarity in antigens. Lines of partial intersection, while implying some interaction, do not concretely confirm that the antigens are not identical as effectively as lines of true intersection do. Thus, lines of intersection serve as a clear and definitive indicator of non-identity between the antigens