Effect of complement on the rheological properties of the erythrocyte membrane

The effect of complement (C) on the erythrocyte deformability was investigated. Sheep erythrocytes (E) were sensitized with specific antibodies (A) and treated with various doses of human C. Gravity filtration of unlysed EAC showed a C dose‐dependent decrease in whole cell deformability, which was shown to be due to an impairment of the membrane rheological properties. As the fluidity of the lipid bilayer, sensed by a spin label, was not modified, the observed effects should be related to an interaction between C and the cytoskeleton. The influence of C3b and C3d in these processes seems unlikely, as similar hemagglutination titers were found, respectively, for anti‐C3c and anti‐C3d antisera against the varying EAC. The study of the degree of spontaneous hemolysis of EAC in buffers with solutes of different Stokes radii showed that differing‐sized functional C lesions were produced, and that the formation of larger‐sized lesions was favored by incubation with higher C doses. These results suggest that the insertion of proteins from the membrane attack complex, C5b–9 (MAC), into the erythrocyte membrane may be responsible for the effect of C on the rheological properties of the erythrocyte membrane.