The present invention clarifies the primary structure of human-originated PGIS and the nucleotide sequence encoding same. The PGIS and its DNA are useful as reagents for the development of therapeutic agents for the cardiovascular diseases induced by the production imbalance between PGI.sub.2 and TXA.sub.2, and as diagnostics for determining the in vivo tissue expression level and distribution of PGIS or mRNA thereof. Moreover, they can be used as therapeutic agents for cardiovascular diseases, which introduce PGIS and the like into human or other animals in a lesion-specific manner. The production method of the present invention is useful for the easy and efficient mass production of the human-originated PGIS. The antibody of the present invention is useful for the purification of the human-originated PGIS and immunohistochemical analysis of the cause of a disease.