Antibody recognition of rodent malaria parasite antigens exposed at the infected erythrocyte surface: Specificity of immunity generated in hyperimmune mice

In regions where malaria is endemic, inhabitants remain susceptible to repe ated reinfection as they develop and maintain clinical immunity. This immun ity includes responses to surface-exposed antigens on Plasmodium sp.-infect ed erythrocytes. Some of these parasite-encoded antigens may be diverse and phenotypically variable, and the ability to respond to this diversity and variability is an important component of acquired immunity. Characterizing the relative specificities of antibody responses during the acquisition of immunity and in hyperimmune individuals is thus an important adjunct to vac cine research. This is logistically difficult to do in the field but is rel atively easily carried out in animal models. Infections in inbred mice with rodent malaria parasite Plasmodium chabaudi chabaudi AS represent a good m odel for Plasmodium falciparum in humans. This model has been used in the p resent study in a comparative analysis of cross-reactive and specific immun e responses in rodent malaria. CBA/Ca mice were rendered hyperimmune to P. chabaudi chabaudi (AS or CB lines) or Plasmodium berghei (KSP-11 line) by r epeated infection with homologous parasites. Serum from P. chabaudi chabaud i AS hyperimmune mice reacted,vith antigens released from disrupted P. chab audi chabaudi AS-infected erythrocytes, but P. chabaudi chabaudi CB and P. berghei KSP-11 hyperimmune serum also contained cross-reactive antibodies t o these antigens. However, antibody activity directed against antigens expo sed at the surfaces of intact P. chabaudi chabaudi-infected erythrocytes wa s mainly parasite species specific and, to a lesser extent, parasite line s pecific. Importantly, this response included opsonizing antibodies, which b ound to infected erythrocytes, leading to their phagocytosis and destructio n by macrophages. The results are discussed in the context of the role that antibodies to both variable and invariant antigens may play in protective immunity in the face of continuous susceptibility to reinfection.