Abstract
Experiments to characterize the immune response induced by the inoculation of infective sporozoites were undertaken in an experimental rodent malaria system. Since earlier work had shown that the blood phase of the infection suppresses the humoral anti-sporozoite response, the development of parasitaemia was completely prevented by treating the animals with either chloroquine or primaquine shortly after sporozoite inoculation. The results obtained by immunization with infective Plasmodium berghei sporozoites were compared with those obtained using γ-irradiated sporozoites, by measuring the antibody levels of the immunized mice and determining their degree of protection against challenge. The level of protection in animals immunized with infective sporozoites and submitted to chloroquine treatment was found to be comparable to that induced with irradiated sporozoites. Under both conditions, a single intravenous inoculation of 10 4 sporozoites protected approximately 50% of the immunized mice from challenge with infective sporozoites. When two immunized doses were given, over 90% of the animals from both groups were protected. Immunization of primaquine-treated animals with infective sporozoites resulted in a somewhat lower level of protection. The antibody response to inoculation of infective sporozoites was either comparable to or somewhat greater than that induced by irradiated sporozoites. In vitro incubation of sporozoites with a high concentration of chloroquine abolished their infectivity. These chloroquine-attenuated sporozoites, however, were immunogenic and induced a protective immune response.
Published Version
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