Alloantigen

Part of speech: noun

Definitions

1. A substance that elicits an immune reaction stemming from its origin in a genetically dissimilar individual of the same species
2. A molecule that triggers an immune response due to being derived from a genetically different organism within the same species
3. A type of antigen that provokes an immune reaction because it originates from a different individual of the same species

Etymology: Alloantigen is a modern scientific coinage, built from two Greek elements. The first, "allo-", comes from Ancient Greek "allos", meaning "other" or "another", and it has passed into English as a prefix in many technical terms. The second part is "antigen", a word that itself combines "anti-", from Ancient Greek "anti" meaning "against" or "opposite", with the French-derived "-gène", meaning "producing" or "generating". An antigen is a substance that provokes an immune response, so the name describes a thing that produces a reaction against it. Put together, "alloantigen" means an antigen that comes from another individual of the same species. The prefix does the distinctive work: a transplanted organ or a donated blood cell can carry molecules that the recipient's immune system recognises as foreign, even though the donor and recipient belong to the same species. The term therefore separates these same-species triggers from antigens that come from entirely different organisms, such as bacteria or viruses.