Monoclonal antibodies react with the apical end of P. falciparum merozoites. Mature schizont stage parasites were dual-labeled with each mouse mAb and rabbit antisera against either PfRAP1 (rhoptry body marker) or PfAMA1 (microneme marker). Nuclei were visualized with DAPI in the merged images shown in the right most panels. DIC, differential interference contrast microscopy. Merge, created by merging the IFA and nuclear-staining images. A representative image out of at least three independent experiments is shown for each mAb. Bars represent 5 mm. Out of the 164 ELISA positive mAbs obtained against immunogens, only 12 (~7%) reacted by IFA against late schizont parasites with a punctate staining pattern suggestive of recognition of merozoite apical organelles. To predict target organelles, dual labeling IFA was performed with PfRAP1 as a rhoptry bulb marker and PfAMA1 as a microneme marker. All 12 selected mAbs colocalized with PfRAP1 but not with PfAMA1, suggesting recognition of the merozoite rhoptry bulb.

Ito D, Chen JH, Takashima E, Hasegawa T, Otsuki H, Takeo S, Thongkukiatkul A, Han ET, Tsuboi T. Identification of a Novel RAMA/RON3 Rhoptry Protein Complex in Plasmodium falciparum Merozoites. Front Cell Infect Microbiol. 2021 10:605367.