Relative membrane rigidity and membrane mechanical stability of variant α-thalassemia RBCs. HbCS/CS RBCs exhibited the greatest increase in membrane rigidity while HbH/CS, HbH, and CS trait RBCs exhibited intermediate increases in membrane rigidity (A). The α-thalassemia-1 trait RBC membranes exhibited normal membrane rigidity (A). Representative membrane mechanical stability data for the variant RBCs are shown (B). The rate of decline of deformability index of membranes from HbCS/CS was the slowest, indicating that these membranes exhibit the greatest increase in membrane mechanical stability. The rate of decline of deformability index of membranes of HbH/CS and HbH RBCs was intermediate between that of HbCS/CS and normal membranes, indicating somewhat less of an increase in membrane mechanical stability. The abbreviations are the same as those in Fig 1.