Rosette formation by Plasmodium coatneyi-infected erythrocytes of the Japanese macaque (Macaca fuscata).

We studied in vitro the spontaneous rosette formation by red blood cells of a Japanese macaque infected with Plasmodium coatneyi, which occurred after 30 hr of incubation. Rosette formation involved 88% of parasitized red blood cells (PRBCs). Spontaneous rosettes were formed when the ring-stage parasites developed into late trophozoites or schizonts. A rosette usually consisted of a PRBC surrounded by three or more uninfected erythrocytes. Electron microscopic examination revealed that interaction with adjacent uninfected erythrocytes in rosettes appeared to be mediated by knobs of PRBCs. Protruding ends of these knobs attached to the membranes of adjacent uninfected erythrocytes. In the present study, we have also obtained evidence that another pattern of cell adhesion was mediated by flat and focal electron-dense knobs that had formed on the membranes of PRBCs.