Determination of the Number of Lytic Sites in Biconcave and Spheroid Erythrocyte Ghosts After Complement Lysis

Abstract

C5b-9 binding to erythrocyte membranes was quantitated with the aid of C7-depleted serum, reconstituted with 125-J-C7. The number of C5b-9 complexes/cell was correlated with the transformation of ghosts from the biconcave to the spheroid shape by the combination of flow cytometry and sucrose density gradient ultracentrifugation. At low complement levels the mean number of C5b-9 complexes ranged from 300 to 1200 complexes/erythrocyte ghost, and biconcave as well as spheroid ghosts were found simultaneously in the same sample. The separation of both types of ghosts by sucrose density gradient centrifugation showed that the irreversible transition from the biconcave to the spheroid form occurred at a critical value of 850 C5b-9 complexes/erythrocyte ghost. Ghosts bearing less than 850 C5b-9 complexes were biconcave, and resealed ghosts bearing more than 850 C5b-9 complexes were spheroid and leaky. The spheroid transition is abrupt; no intermediate forms could be detected. The spheroid transformation is interpreted as a direct interaction between the C5b-9 complexes and membrane proteins resulting in a disturbance of the cytoskeleton of the erythrocyte ghost followed by spheroidization.