What does epitope mean?
An epitope is the precise portion of an antigen—a foreign substance such as a protein on a virus or bacterium—that is recognized by the immune system. When an antibody or a T-cell receptor binds to an epitope, it is effectively latching onto a small, distinctive patch of the antigen's surface, and this interaction is what launches an immune response. Immunologists distinguish linear epitopes, which are short stretches of amino acid sequence, from conformational epitopes, which are formed when distant parts of a folded molecule come together in three-dimensional space. Identifying which epitopes a vaccine or infection exposes to the immune system—through techniques such as epitope mapping—is central to vaccine design, diagnostics, and therapeutic antibody development. Although epitope belongs firmly to technical vocabulary, it has become increasingly familiar as immunology features in public discussion of vaccines and infectious disease.
nounThe specific part of an antigen that is recognized and bound by an antibody, B-cell receptor, or T-cell receptor; in effect, the molecular 'target site' that triggers an immune response.
- Immunology: the region of an antigen recognized by an antibody or T-cell receptor, also called an antigenic determinant.
"The vaccine was designed to present a single viral epitope to the immune system."
"Researchers mapped every epitope on the protein's surface before designing the antibody."
"A single mutation can hide a key epitope, allowing the pathogen to slip past existing antibodies."
Regular plural; standard in all varieties of English.
"The analysis identified several distinct epitopes across the protein's surface."
Your immune system doesn't recognize a virus as a whole — it recognizes tiny molecular fingerprints called epitopes, sometimes just a handful of atoms wide.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of epitope
Epitope was coined in the mid-20th century within immunology, combining the Greek-derived prefix 'epi-' (meaning 'upon' or 'on') with '-tope', from Greek 'topos' meaning 'place'. It was formed alongside related terms such as 'paratope' to name the complementary sites involved in antigen–antibody binding. The same Greek root 'topos' underlies English words such as 'topology', 'topic', and 'utopia'.
Related word forms
How epitope is actually used
Strictly a technical term of immunology and biochemistry; it is rare outside scientific literature. It is a countable noun with a regular plural ('epitopes'). The adjective form 'epitopic' exists but is used mainly in specialist writing.
Easily confused with epitope
An epitope is the site on the antigen that is bound; the paratope is the corresponding site on the antibody that does the binding.