EBA-175 is shed at or around the point of erythrocyte invasion and retains region VI. (C) IFA images of an acetone-fixed segmented 3D7 schizont and free merozoites dual labeled after fixation with mAb 1E1 (anti-MSP119; red) and anti–region VI antibodies (green). The punctate, apical pattern obtained with the latter is typical of microneme staining. (D) EBA-175 is discharged onto the apical surface of free merozoites. Merozoites released from 3D7 schizonts in the presence of anti–region VI antibodies were washed, fixed, and probed with FITC anti-mouse IgG to detect bound anti–region VI antibodies (green), followed by mAb 1E1 (anti-MSP119; red). Many free merozoites exhibit a strong apical FITC signal (thin arrows), whereas residual intact schizonts containing merozoites that were not accessible to the anti–region VI antibodies show only background FITC labeling (thick arrows). No signal was associated with merozoites released in the presence of preimmune mouse antisera (unpublished data). (E) IFA images of newly invaded (≤3-h-old) ring-stage 3D7 parasites probed with anti–region VI antibodies after acetone fixation. Most rings did not react at all with the antibodies. Nuclei were stained with DAPI (blue). Bars, 5 μm.

O'Donnell RA, Hackett F, Howell SA, Treeck M, Struck N, Krnajski Z, Withers-Martinez C, Gilberger TW, Blackman MJ. Intramembrane proteolysis mediates shedding of a key adhesin during erythrocyte invasion by the malaria parasite. J Cell Biol. 2006 174:1023-33.