In contrast, a linear epitope is formed by the 3-D conformation adopted by the interaction of contiguous amino acid residues.
A linear epitope is not determined solely by the primary structure of the involved amino acids.
T cell epitopes presented by MHC class I molecules are typically peptides between 8 and 11 amino acids in length, whereas MHC class II molecules present longer peptides, 13–17 amino acids in length,[10] and non-classical MHC molecules also present non-peptidic epitopes such as glycolipids.
The part of the antigen that immunoglobulin or antibodies bind to is called a B-cell epitope.
This property is exploited by the immune system in regulation by anti-idiotypic antibodies (originally proposed by Nobel laureate Niels Kaj Jerne).
[20] Methods for structurally mapping epitopes include X-ray crystallography, nuclear magnetic resonance, and electron microscopy.
[20] X-ray crystallography of Ag-Ab complexes is considered an accurate way to structurally map epitopes.
[20] Electron microscopy is a low-resolution method that can localize epitopes on larger antigens like virus particles.
[20] B-cell epitope mapping can be used for the development of antibody therapeutics, peptide-based vaccines, and immunodiagnostic tools.
Using recombinant DNA techniques genetic sequences coding for epitopes that are recognized by common antibodies can be fused to the gene.
Following synthesis, the resulting epitope tag allows the antibody to find the protein or other gene product enabling lab techniques for localisation, purification, and further molecular characterization.