Major granular component involved in excreted-secreted antigen (ESA) immunity. Possibly acts in conjunction with GRA1. Located in dense granules of tachyzoites. Upon infection, secreted, in a Ca(2+)-dependent manner, into the parasitophorous vacuole (PV) and targeted to the microvillus membranous network. May also be O-glycosylated. The N-terminus is blocked. This protein is one of the antigens specifically recognized by patients infected by Toxoplasma gondii. Possible candidate for an effective vaccine - of special value for immunocompromised patients such as those with AIDS or neoplastic disease.