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To block the renin-substrate reaction by immunological tools is a long-standing dream. Since 1951 active immunization and the passive transfer of antirenin antisera have been successfully carried out in different species and in different experimental models of hypertension and normotension. These studies indicated that renin is a powerful immunogenic protein, capable of breaking down self-tolerance in different species. In this initial period the most significant results were obtained with hog renin. Passive transfer of antisera raised against hog renin or active immunization with hog renin was able to decrease blood pressure in renovascular or essential hypertension in dogs. Renin was semipurified and injected without adjuvant, however, since there was no method for determining plasma renin activity. Recently, complete purification of murine and human renin has allowed an extension of this approach, using the passive transfer of antirenin polyclonal antisera or monoclonal antibodies. Active immunization against pure human renin was successful in normotensive marmosets. This immunization with a nearly homologous renin in a primate model induced a significant decrease in blood pressure, associated with a complete disappearance of plasma renin activity. Unfortunately this powerful immunization was associated with an autoimmune disease that is specific for the kidney, related to self-recognition of the production site of renin by antibodies and lymphocytes. Similar results were reported with the use of mouse submandibular gland renin as an immunogen in spontaneously hypertensive rats (SHR). This manipulation decreased blood pressure in SHR to a level near that of normotensive Wistar-Kyoto control rats. However, again the animals showed a severe autoimmune disease of the kidney. In parallel, the recent determination of the sequence of human and rat renin from the structure of its DNA has permitted the construction of synthetic peptides mimicking epitopes of the native protein. The synthetic vaccine approach was thus developed to demonstrate the ability of antibodies raised against synthetic epitopes to bind and to inhibit the enzymatic activity of the native renin.