Antigen

Part of speech: noun

Definitions

1. A substance that triggers an immune response by causing the body to produce antibodies against it
2. A substance recognized by the immune system that prompts the production of antibodies or activates immune responses against pathogens
3. A foreign substance that induces an immune response by stimulating the production of antibodies or activating various immune functions

Etymology: The name describes a function, not a substance. "Antigen" was built in French from two Greek-derived parts: "anti-", meaning "against", and "gène", meaning "generator" or "producer". Taken together, an antigen is something that generates a response against it. The first part comes from ancient Greek "anti", a preposition meaning "against", "opposite" or "in place of", which also gave English words like "antidote" and "antibody". The second part is the French "gène", from the Greek root "genes", meaning "born" or "produced", the same root behind "gene" and "genesis". Early immunologists combined these pieces to name the substance that prompts the body to produce its defensive proteins. The result is a word that is transparent in a way many scientific terms are not: its parts tell you the whole story. English adopted it directly from French, so it is a borrowing rather than a word that passed through Latin first.

Synonyms: immunogen, substance