Further evidence for immune cytolysis by antibody and the first eight components of complement in the absence of C9.

The reported observations on the slow, low-grade lysis of EAC1-8 were re-examined by using antisera to guinea-pig C9 as a specific inhibitor against C9 to eliminate the possibility that C8 preparations might contain C9 which lyses EAC1-8. Pretreatment of C8 preparation with IgG fraction of the anti-C9 did not result in reduction of the degree of lysis of EAC1-7 by C8. The dose response curve in titration of C8 with EAC1-7 in the absence of C9 was sigmoidal and completely different from that in the presence of excess C9, suggesting that the cell membrane damage caused by C8 might not be the same as that by C9. Sensitized nucleated cells were shown to be lysed similarly by the first eight components of complement, namely C1 to C8.