Effect of route of Mycobacterium bovis BCG administration on induction of suppression of sporozoite immunity in rodent malaria.

Intravenous immunization of mice with 16,000, 60Co--gamma-irradiated, attenuated sporozoites produced solid immunity to sporozoite-induced malaria when the mice were challenged 21 days after immunization. In contrast, mice injected by various routes with 10(7) viable units of Mycobacterium bovis (BCG) before immunization with irradiated sporozoites were not completely immune to challenge. The extent of reduced protection against viable sporozoites demonstrated with these animals was dependent upon the injection route mycobacteria. The intravenous administration of BCG induced the greatest degree of suppression, followed by the intraperitoneal and subcutaneous routes. BCG injected intramuscularly before sporozoite immunization did not suppress development of immunity. In contrast, mice injected with BCG after immunization with attenuated sporozoites exhibited a lesser degree of suppression. In these animals, only the intravenous injection of mycobacteria reduced immunity.