Size and quality of rosettes are determined by multiple serum components.

Rosettes visualized by immunofluorescence in the presence of ethidium bromide to stain parasite nucleic acid (× 1000 objective in incident ultraviolet light) showing the difference between the effect of individual and combined serum fractions. (A) Small rosettes formed in the presence of individual serum fractions. The adhesion between the cells was weak, and the rosettes sometimes fell apart. Panel 1, conA-unbound fraction, C1; panel 2, anion exchange-unbound fraction, A1; panel 3, IgM affinity-unbound fraction, M1. (B) Large rosettes formed in the presence of whole serum or combined fractions. These rosettes were robust and stable, the interaction between the cells was strong, and the rosettes did not fall apart. Panel 1, conA-unbound fraction C1 + bound fraction C2; panel 2, anion exchange-unbound fraction A1 + gradient fraction GF4; panel 3, IgM affinity-unbound fraction M1 + bound fraction M2 (ie, IgM).