Antigenic variation in Plasmodium chabaudi chabaudi AS
Plasmodium chabaudi has been shown to undergo antigenic variation during the course of infection in mice. The importance of this model is the similarity and applicability of its features to infection of humans in P. falciparum. This thesis presents work performed using P. chabaudi to study various aspects of antigenic variation in asexual erythrocytic malaria parasites. The course of infection of P. chabaudi in N1H mice shows an initial acute parasitaemia which clears to subpatency. This is usually followed, after a period of days, by a second, and occasionally a third, recrudescent parasitaemia of lesser magnitude and duration. A cloned parent parasite population and cloned parasite populations derived from a recrudescence of the parent were tested in an indirect fluorescent antibody test on live, schizont-infected RBC (live IFAT) using a panel of hyperimmune sera raised against these populations and against one of the recrudescent clones after mosquito transmission. This test can detect antigens on the surface of parasitised RBC. The results of this analysis indicated that all the recrudescent clones were antigenically different from the parent and some were different from each other. In total, including the parent, six variant antigen types (VATs) were identified. Some of these also appeared to vary in immunogenicity. The effects of mosquito transmission on expression of variant antibodies was also examined using the panel of hyperimmune sera in the live IFAT. Mosquito transmission of two antigenically distinct recrudescent clone populations resulted in a change in antigenicity of both types to an apparently similar VAT, which had the same apparent identity as that of the original, post mosquito transmission but pre-cloning, parent population.