Localization of PfEMMA1 with immunogold electron microscopy. Late-stage infected RBCs were probed with mouse anti-PfEMMA1 fragment 2 antibodies (6-nm gold particles; black arrows) and rabbit anti-GPC (10-nm gold particles; red arrows). (A and B) In a representative live, non-permeabilized iRBC, PfEMMA1 localized to the exofacial surface of the RBC membrane in close proximity to a knob with a characteristic electron-dense layer under the RBC surface membrane. Approximately 7% of infected RBCs had evidence of exofacial surface labeling. (C–F) In permeabilized iRBCs, PfEMMA1 localized to MCs, the parasite surface, and an electron-dense knob on the iRBC surface membrane. Scale bars, 0.5 μm (A, C, and E) or 200 nm (B, D, and F). We detected PfEMMA1 labeled with clusters of immunogold-conjugated anti-PfEMMA1 antibodies in various locations: (a) on the exofacial surface of live, nonpermeabilized iRBCs in close proximity to a knob, with its characteristic electron-dense layer underlying the RBC membrane (A and B), and (b) on the surface of MCs within an iRBC (C and D), on an electron-dense knob and on the surface of an intact parasite (E and F) within permeabilized parasites treated with equinatoxin II (EqtII).
Michelow IC, Park S, Tsai SW, Rayta B, Pasaje CFA, Nelson S, Early AM, Frosch AP, Ayodo G, Raj DK, Nixon CE, Nixon CP, Pond-Tor S, Friedman JF, Fried M, Duffy PE, Le Roch KG, Niles JC, Kurtis JD. A newly characterized malaria antigen on erythrocyte and merozoite surfaces induces parasite inhibitory antibodies. J Exp Med. 2021 218(9):e20200170.