Plasmodium falciparum Erythrocyte Invasion: Combining Function with Immune Evasion
Figure 2
Plasmodium merozoites face an array of immunological challenges.
Merozoites are the only extracellular stage of the Plasmodium life cycle and are therefore exposed to an array of immune attack mechanisms, as illustrated in cartoon form. Merozoite antigens are known to be the target of antibody responses, which operate both by opsonisation leading to phagocytosis and by simple steric hindrance of receptor–ligand interactions critical for invasion. Complement deposition on the merozoite surface may also play a role in parasite clearance. To avoid these attack mechanisms, Plasmodium parasites have evolved a number of distinct evasion responses. Some merozoite antigens such as AMA1 are highly polymorphic, while members of the PfRH and EBA multigene families are largely redundant and have variable expression profiles. Both of these strategies slow the development of protective immunity by forcing the antibody response to efficiently recognize multiple targets in order to mount an effective response. Finally, RH5 appears to be poorly immunogenic in the context of natural infections, perhaps due to limited levels of expression and exposure.