Ma'anar ƙamus na kalmar "immunogen" wani abu ne, yawanci furotin ko polysaccharide, wanda ke da ikon haifar da amsawar rigakafi a cikin jiki, musamman samar da ƙwayoyin rigakafi. Immunogen na iya zama wani bangare na kwayoyin halitta, kamar kwayoyin cuta ko kwayar cuta, ko kuma yana iya zama wani abu na waje, irin su pollen ko guba, wanda ke shiga cikin jiki kuma tsarin rigakafi ya gane shi ba kansa ba ne. Lokacin da tsarin rigakafi ya gano immunogen, yana ɗaukar martani don kawar da barazanar da ake gani.