Placental Chondroitin Sulfate A–Binding Malarial Isolates Evade Innate Phagocytic Clearance

Abstract

Pregnancy-associated malaria is characterized by the accumulation of parasitized erythrocytes (PEs) and monocytes in the placenta, and they are believed to directly contribute to adverse birth outcomes. Although most parasite isolates adhere to CD36, placental isolates express novel variant surface antigens (VSAs) and bind to chondroitin sulfate A (CSA). CSA-binding PEs are rarely observed outside of pregnancy, and most primigravid women lack immunity and must rely on innate immune mechanisms to clear these placental parasite variants. We hypothesized that differences in VSA expression and adhesive phenotype between pregnancy-associated (CSA-binding) and non–pregnancy-associated (CD36-binding) isolates may have direct implications for the failure of primigravid women to control the placental parasite burden through innate phagocytic pathways. We demonstrate here, both in vitro and in vivo, that there is a nonopsonic phagocytic defect for CSA-binding PEs. The ability of CSA-binding PEs to evade innate clearance pathways may contribute to the parasite accumulation and recruitment of monocytes that characterize placental malaria