Antigen that enters the body of the organism from the outside, e.g. through inhalation, ingestion, or injection.
Exogenous antigens include particles considered foreign within the organism. For example, allergens (such as pollen), proteins from transplanted tissues and organs, and parts of microorganisms (such as coat, capsule, cell wall, flagella, fimbria, or toxin of bacteria, viruses, etc.) can serve as antigens.
Word origin: French exogène : Greek exō-, exo– (outside) + French –gène, –gen (yielding, producing) + antigen.
Compare: endogenous antigen
See also: antigen