Plasmodium falciparum ring-infected erythrocyte surface antigen is released from merozoite dense granules after erythrocyte invasion.

Electron microscopy was used to study the fate of Plasmodium falciparum ring-infected erythrocyte surface antigen after merozoite invasion by using postembedding immunolabeling. The antigen was localized to small dense granules located centrally or laterally in free merozoites. In newly invaded erythrocytes, labeling was found in pockets of the parasitophorous vacuole space or in aggregates closely associated with the parasitophorous vacuole. These patterns indicate that ring-infected erythrocyte surface antigen is contained in merozoite dense granules that are released after merozoite invasion and not via apical rhoptry ducts at the time of merozoite attachment.