Inhibition of complement-induced [14C]sucrose release by intracellular and extracellular monoclonal antibodies to C9: evidence that C9 is a transmembrane protein.

Monoclonal antibodies to the terminal component of the human complement pathway, C9 were used to inhibit the complement-induced release of entrapped [14C]sucrose from erythrocyte ghosts. Antibodies were present either outside, or entrapped within the ghosts. Different monoclonal antibodies were demonstrated to inhibit [14C]sucrose release depending on whether the antibody was outside or entrapped within the ghosts. These findings demonstrate that C9 within the membrane attack complex on erythrocyte membranes is an asymmetrical transmembrane protein penetrating into the cytoplasmic space.