Long‐lived P lasmodium falciparum specific memory B cells in naturally exposed S wedish travelers

Antibodies ( A bs) are critical for immunity to malaria. However, P lasmodium falciparum specific A bs decline rapidly in absence of reinfection, suggesting impaired immunological memory. This study determines whether residents of S weden that were treated for malaria following international travel maintained long‐lasting malaria‐specific A bs and memory B cells ( MBC s). We compared levels of malaria‐specific A bs and MBC s between 47 travelers who had been admitted with malaria at the Karolinska University Hospital between 1 and 16 years previously, eight malaria‐naïve adult S wedes without histories of travel, and 14 malaria‐immune adult K enyans. P lasmodium falciparum ‐lysate‐specific A b levels were above naïve control levels in 30% of the travelers, whereas AMA ‐1, merozoite surface protein‐1 42 , and merozoite surface protein‐3‐specific A b levels were similar. In contrast, 78% of travelers had I g G ‐ MBC s specific for at least one malaria antigen (59, 45, and 28% for apical merozoite antigen‐1, merozoite surface protein‐1, and merozoite surface protein‐3, respectively) suggesting that malaria‐specific MBC s are maintained for longer than the cognate serum A bs in the absence of re‐exposure to parasites. Five travelers maintained malaria antigen‐specific MBC responses for up to 16 years since the diagnosis of the index episode (and had not traveled to malaria‐endemic regions in the intervening time). Thus P . falciparum can induce long‐lasting MBC s, maintained for up to 16 years without reexposure.