Comparative morphological and rheological characteristics of P cynomolgi and P vivax infected RBCs. (A) The morphologic similarity of P cynomolgi early trophozoites (18-24 hours after invasion) in M mulatta normocytes and human reticulocytes compared with that of P vivax in human reticulocytes. Giemsa-stained thin film smear is the most commonly used method for species diagnosis in areas where P vivax and P cynomolgi are co-endemic. Scale bar = 10 μm. (B) The effect of P cynomolgi invasion and development on the deformability of monkey and human RBCs. The plot shows the membrane mean shear modulus (SM) (a higher SM indicates a reduced membrane deformability) for different RBC types (monkey and human) and stages of P vivax erythrocytic development (geometric mean ± 95% confidence intervals; n > 15 cells from 3 independent trials). The red lightning icons indicate the tropism of P cynomolgi when invading human or monkey RBCs. Pictures of respective cell types before and during membrane SM measurement by micropipette aspiration are shown under the graph. Mean (geometric) SMs were compared by using ANOVA (Bonferroni correction) and multiple comparison test (Tukey). Uninfected normocytes were significantly more deformable than uninfected reticulocytes (P < .001). However, both ring and trophozoite P vivax stages become progressively more deformable (P < .05) until schizont stage (the very mature schizonts segmenters were especially rigid). Scale bar = 5 μm. (C) Comparative phenotypic characterization of caveolae in P cynomolgi- and P vivax–infected RBCs in monkeys and humans as revealed by atomic force microscopy. (D) The mean density of caveolae per μm2 (n > 10 cells scanned for each condition over 3 separate ex vivo maturation experiments) on early and late trophozoite-infected RBCs. (E) The mean diameter of caveolae of P vivax and P cynomolgi in human reticulocytes. No significant difference in caveola density or diameter was observed.
