Figure 3.
Biomechanical properties of the RBC membrane differ across Dantu genotypes and correlate with invasion. (a) Membrane flickering spectrometry enabled measurement and comparison of RBC bending modulus, tension, radius, and viscosity across genotypes (n=6 RBCs per genotype). Mean and standard deviation were obtained from the averages of cell tensions for each sample: non-Dantu RBCs - (6.0 ±1.9) *10−7 N/m; Dantu heterozygotes - (7.9±2.8) *10−7 N/m; Dantu homozygotes - (8.8 ± 0.7) *10−7 N/m. The impact of tension on parasite invasion was evaluated by simultaneously measuring tension from flickering analysis and live video imaging of the invasion process from rupturing schizonts (“egress”, “deformation”, then either “invasion” and “echinocytosis”, or a failed invasion) (b), in non-Dantu and Dantu homozygote RBCs (c). The threshold range for tension, marked in (a) and (c), was obtained by comparing distributions of tension across Dantu genotypes with their invasion efficiency. (d) The contact region between merozoites and RBCs, represented in the snapshots, was measured during pre-invasion at the point of RBC maximum deformation for 2 sets of very high (n = 15) and low tension (n = 23) cells (p=1.30 × 10−32). Merozoite-RBC contact section was significantly smaller in high tension RBCs meaning that parasites were much more wrapped around RBCs with a lower membrane tension. (e) Parasite invasion efficiency and RBC tension for six increasing concentrations of glutaraldehyde (0.00001 - 0.01%). Parasite invasion was significantly decreased for RBC tensions around 8.8 × 10−7 N/m (22% decrease) and 12.2 × 10−7 N/m (43% decrease). Median values are reported from 2 technical replicates of 2 biologically independent samples. Pairwise comparisons between genotypes used the two-sided Mann-Whitney U test. ** p < 0.01. Number of cells and tension reported in Supplementary Tables 5, and 6.