P vivax rosetting preference. (A) Percentage of rosettes associated with at least 1 reticulocyte in P vivax and P falciparum isolates in patient isolates already containing late-stage parasites (no ex vivo maturation). (B) Differences in rosetting rate of P vivax and P falciparum isolates in environment with <1% reticulocytes and approximately 50% reticulocytes (achieved by concentrating host reticulocytes on a 75% Percoll gradient). Lines connect paired observations. Altering the reticulocyte concentration had little effect on P vivax rosette formation; however, the number of normocytes attached to the P vivax IRBC was notably reduced in the treatment of enriched reticulocytes. Interestingly, an increase in the available reticulocytes reduced the ability of P falciparum to rosette (P < .01). (C) Reticulocytes were rarely associated with rosettes irrespective of the group or species observed. Here, a single normocyte is rosetting on a P vivax schizont (red arrow). The yellow arrows point to Heilmeyer stage IV reticulocytes subvitally stained with Giemsa. The tip of a glass micropipette with an internal diameter of 6 um is shown for scale.