Figure 5. The effect of PfEMP1 antibodies on rosetting in static and flow assays with parasite strain TM284R+.

Antibodies to the NTSDBLα region of the PfEMP1 variant TM284var1 were added to TM284R+ parasite culture suspension at a final concentration of 100, 10 and 1 µg/ml of antibodies and incubated for 30 mins before assessment of rosetting. The control was a culture suspension with no added antibody. A) Static assay: the percentage in IEs in rosettes (rosette frequency) was assessed by fluorescence microscopy of ethidium bromide-stained wet preparations. B) Flow assay using combined data from experiments at 0.5, 0.75 and 1.0 dyn/cm². The total rosette area (µm²) from 10 fields (20× objective) was determined after 5 minutes under flow at each shear stress using ImageJ software. C–E) To allow direct comparison of the results from static and flow assays, the rosetting values from each experiment were converted to a percentage of the “no additive” control value. C) TM284R+ parasites with 100 µg/ml PfEMP1 antibody. D) TM284R+ parasites with 10 µg/ml PfEMP1 antibody. E) TM284R+ parasites with 1 µg/ml PfEMP1 antibody. Mean and standard error from four independent experiments (A and C–E), or twelve experiments (B) are shown. Mean values that are statistically significantly different from the control value (A–B) or the static value (C–E) by one-way ANOVA with Tukey’s post test are shown by asterisks, *p<0.05.