Epitope
Definition
The specific region of an antigen that makes physical contact with an antibody's binding site (paratope). Also called the antigenic determinant. A single protein may carry ten or more distinct epitopes, each recognised by a different antibody. Epitope mapping is used in diagnostic antibody development and in cross-reactivity studies.
- Synonym
- Antigenic determinant
- Typical size
- 5 to 15 amino acids, or a few sugar residues
- Epitopes per protein
- Often ten or more distinct sites on one protein
- Binds to
- Paratope, the antibody's variable-region binding site
Common questions
How does epitope mapping differ from simply confirming an antigen is present?+
Epitope mapping identifies exactly which surface region an antibody binds, which matters for choosing antibody pairs that do not compete for the same site and for predicting cross-reactivity with related proteins.
Why can two antibodies raised against the same antigen give different results?+
They may target different epitopes on the same molecule. One epitope can be masked by folding, glycosylation or degradation while another remains exposed, so assay sensitivity depends on which epitope the antibody recognises.
Related terms
- Antigen
- A molecule recognised by the adaptive immune system through specific binding to an antibody or T-cell receptor. Defined by immunogenicity (capacity to...
- Cross-Reactivity
- The capacity of an antibody raised against one analyte to bind structurally related compounds. In RIA, cross-reactivity is the main driver of...
- Hapten
- A small molecule with antigenicity but no immunogenicity on its own. Haptens must be conjugated to a carrier protein to raise antibodies....
- Immunogen
- A molecule that is both immunogenic (triggers antibody production) and antigenic (binds those antibodies). Used interchangeably with 'complete antigen'. Most protein antigens...
- Secretor Status
- A genetic trait that determines whether a person expresses their ABO blood group antigens in secreted body fluids such as saliva, semen,...