Synthetic peptides versus natural antigens in immunoassays

Although most antigenic determinants of proteins are discontinuous, it is nevertheless possible to mimic such epitopes by means of linear, synthetic peptides. When such peptides are found to cross-react with antiprotein antibodies or when they are able to induce antibodies that cross-react with the parent protein, the peptides are labelled continuous epitopes. Many algorithms have been developed to predict the location of continuous epitopes in proteins, but their rate of successful prediction is not very high. The use of synthetic peptides corresponding to a single continuous epitope increases the specificity of an immunoassay in the same way that monoclonal antibodies recognizing a single epitope do compared to polyclonal antiserum. When used in solid phase assays, the peptides can be adsorbed directly to the plastic of microtiter plates or they can be used as peptide carrier conjugates. In the case of viral proteins or autoimmune antigens that are difficult to purify and prepare in large amounts, there is considerable advantage in using synthetic peptides instead of the intact protein. Several examples of the use of peptides in the diagnosis of viral and autoimmune diseases will be presented.