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 repeated reinfection as they develop and maintain clinical immunity. This immunity includes responses to surface-exposed antigens on Plasmodium sp.-infected 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 vaccine research. This is logistically difficult to do in the field but is relatively easily carried out in animal models. Infections in inbred mice with rodent malaria parasite Plasmodium chabaudi chabaudi AS represent a good model for Plasmodium falciparum in humans. This model has been used in the present study in a comparative analysis of cross-reactive and specific immune 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 repeated infection with homologous parasites. Serum from P. chabaudi chabaudi AS hyperimmune mice reacted with antigens released from disrupted P. chabaudi chabaudi AS-infected erythrocytes, but P. chabaudi chabaudi CB and P. berghei KSP-11 hyperimmune serum also contained cross-reactive antibodies to these antigens. However, antibody activity directed against antigens exposed at the surfaces of intact P. chabaudi chabaudi-infected erythrocytes was mainly parasite species specific and, to a lesser extent, parasite line specific. Importantly, this response included opsonizing antibodies, which bound to infected erythrocytes, leading to their phagocytosis and destruction 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.