Age-Dependent Acquired Protection against Plasmodium Falciparum in People HavingTwo Years Exposure to Hyperendemic Malaria

摘要

Acquired protective immunity against malaria improves over a lifetime ofcontinuous heavy exposure. Children in endemic areas suffer frequent and severe malaria, but adults usually have seemingly innocuous low-grade parasitemias during their less frequent episodes. Maternal immunity in the neonate wanes within one or two years after birth and a so-called anti-toxic immunity quickly develops, which manifests as tolerance to high-grade parasitemias. Beginning at about age 5, there may be noticeably less frequent and lower-grade parasitemias, and this trend continues gradually through childhood and into adulthood. The resulting protective mechanism of immunologic factors associated with so many years of heavy exposure is not understood, but most often suggested is a process whereby individuals gain an increasing number of effector and memory lymphocytes expressing high-affinity antigen-specific receptors that may react with an increasingly large proportion of epitopes occuring on the parasite.