Crossreactivity with sporozoites, exoerythrocytic forms and blood schizonts of Plasmodium berghei in indirect fluorescent antibody tests with sera of rats immunized with sporozoites or infected blood

IFA studies are reported using plasmodial antigens from 3 different stages of the life cycle of Plasmodium berghei: sporozoites (SP); exoerythrocytic schizonts in rat liver (EEF); and parasitized rat erythrocytes (SCH = schizonts). Two series of specific sera were applied: sera from adult rats with a blood-induced infection (series A) and sera from rats immunized against sporozoites by mosquito bites and protected against parasitemia by chloroquine (series B). In series A antibody titres with all 3 antigens were seen, but those with SCH were generally the highest. Superinfection with parasitized rat blood did not change the titre. In series B sera, collected from rats after a single exposure to infected mosquitoes, showed only titres with SP from day 3 onwards, but after a second exposure titres to all 3 antigens developed. Cross reactivity with the heterologous antigens in series B was clearly less than in series A. Anti-P. berghei sporozoite antibodies did not cross react with P. vivax sporozoites. Rats of series A were resistant to a challenge of parasitized blood and could also inhibit the development of sporozoites. Rats of series B were protected against a challenge of sporozoites but not of infected blood. The results are discussed.