In order to be consistent across all publications, the IEDB defines an epitope as peptides less than or equal to 50 amino acids in size and non-peptidic structures less than or equal to 5000 Daltons. These structures must be experimentally tested for binding to an adaptive immune receptor (T cell receptor (TCR), antibody or B cell receptor (BCR), or major histocompatibility complex (MHC)) or the receptor must be known and stated to be epitope specific in order to be included in the IEDB.
Please see our full inclusion criteria at this link:
Users can easily narrow search results to include only linear peptidic epitopes, discontinuous peptidic epitopes, or non-peptidic epitopes. Peptidic epitopes may also be searched upon using any specific amino acid sequence, with the additional feature of being able to search for epitopes homologous to the input sequence at 70%, 80%, or 90% identity or using a substring match. Non-peptidic epitopes may be searched upon by textual name or via the Molecule Finder which presents all non-peptidic epitopes in a molecular hierarchy provided by Chemical Entities of Biological Interest (ChEBI). Please see the article on IEDB Antigens for more information on how to use the Molecule Finder at this link:
Note that in the IEDB positive epitopes are defined as those having at least one positive measurement and negative epitopes are defined as those having only negative measurements across all publications describing that particular epitope. It is possible for a positive epitope to have some negative assays.