Plasmodium berghei: suppression of antibody response to sporozoite stage by acute blood stage infection.

Mice infected with the erythrocytic stages of show an impaired host response to immunization with irradiated sporozoites of the same malarial parasite. The stage-specific anti-sporozoite response was measured by indirect immunofluorescence upon adsorption of the sera with parasitized red blood cells. -infected mice, immunized with irradiated sporozoites on the fourth day of a blood-induced malaria infection, developed a normal anti-sporozoite antibody response. However, this antibody response was more short-lived compared with the antibody response in normal mice immunized with a similar dose of irradiated sporozoites. The immune response was severely depressed when the animals were immunized on day 7 or later after malaria infection. None of the sporozoite-immunized animals, including those which responded to the first immunization, developed a secondary antibody response on reinoculation with irradiated sporozoites. A fully established anti-sporozoite immune response, obtained after multiple immunizations with irradiated sporozoites and which resulted in stage-specific protection of the animals, was not affected by a superimposed blood stage malaria infection. The titres of the anti-sporozoite antibodies in these animals were unaltered, in spite of their high parasitaemias. Reduction of the malaria parasitaemia by chloroquine treatment abolished the immunosuppressive effects of the disease. These observations are discussed in relation to anti-sporozite immunity and immunosuppression in man in malaria endemic areas.