Plasmodium yoelii can ablate vaccine-induced long-term protection in mice.

Malaria is a serious cause of morbidity and mortality for people living in endemic areas, but unlike many other infections, individuals exposed to the parasite do not rapidly become resistant to subsequent infections. High titers of Ab against the 19-kDa C-terminal fragment of the merozoite surface protein-1 can mediate complete protection in model systems; however, previous studies had not determined whether this vaccine generated long-term protection. In this study, we report that functional memory cells generated by merozoite surface protein-1, per se, do not offer any protection. This is because the parasite induces deletion of vaccine-specific memory B cells as well as long-lived plasma cells including those specific for bystander immune responses. Our study demonstrates a novel mechanism by which Plasmodium ablates immunological memory of vaccines, which would leave the host immuno-compromised.