How does the specificity to bind to antibody differs between 'hot' and 'cold' antigen in radioimmunoassay?
The specificity is the same, but protein-ligand binding is an equilibrium process. In other words, the antigen is constantly associating with and dissociating from the antibody. As a hot antigen dissociates, it is possible that a cold antigen can take its place, and vice-versa. As the ratio of cold to hot antigen increases, there is a greater probability that cold antigens will take the place of hot antigens.

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