Each individual antibody protein is capable of binding specifically with one unique epitope thanks to the unique Antigen Binding Site located at the tip of the variable region on the antibody. This specificity allows precise detection of a target antigen such as a protein while avoiding detection of unrelated proteins that are not of interest.
However, it is important to recognize that a particular epitope could potentially appear on more than one protein antigen. So, one antibody could potentially recognize two or more proteins if these proteins are highly homologous and contain the same epitope.
Also, it is important to recognize that multiple antibodies will be generated against a typical protein antigen and so any one of these antibodies could potentially cross-react with another protein that contains the same epitope(s).
This brings up the issue of how antibodies are typically used, since they can be collected directly from the serum or by isolating the B cell(s) that is producing the antibody of interest. These two antibody production techniques will be discussed on the Polyclonal vs Monoclonal Antibodies page.
Also, because serum contains antibodies against so many antigens (not just the protein that may have been used for immunizations), specificity is typically very low with raw serum. Techniques for increasing specificity will be discussed on the Monoclonal Antibody Alternative page.
So overall, in general terms, antibody specificity helps us discuss if the antibody that we are using in our research (whether it’s a single antibody from a B cell or a pool of antibodies from serum) is able to detect our target protein specifically without cross-reacting with non-specific proteins.