CD59 Efficiently Protects Human NT2‐N Neurons Against Complement‐mediated Damage

The complement regulatory protein CD59 controls cell survival by the inhibition of C5b–9 formation on the cell membrane. Loss of CD59 increases the susceptibility of cells to complement‐mediated damage and lysis. Deposition of IgM can induce complement activation with subsequent cell death. We have previously demonstrated the presence of CD59 on human NT2‐N neurons. In this study, we investigated the functional role of CD59 for NT2‐N cell survival after IgM‐mediated complement activation. Complement activation was induced on NT2‐N neurons with human serum following incubation with the IgM monoclonal antibody A2B5 reacting with a neuronal cell membrane epitope. Deposition of C1q and C5b–9 was detected on the cell membrane and sC5b–9 in the culture supernatant. Specific inhibition of complement was obtained by the C3 inhibitor compstatin, and by anti‐C5/C5a MoAb. CD59 was blocked by the MoAb BRIC 229. Membrane damage of propidium iodide‐stained NT2‐N cells was confirmed by immunofluorescence microscopy and degeneration of neuronal processes was shown with crystal violet staining. A2B5, but not the irrelevant control IgM antibody, induced complement activation on NT2‐N neurons after incubation with a human serum, as detected by the deposition of C1q. A marked membrane deposition of C5b–9 on NT2‐N neurons with accompanying cell death and axonal degeneration was found after the blocking of CD59 with MoAb BRIC 229 but not with an isotype‐matched control antibody. Compstatin and anti‐C5 monoclonal antibodies which blocked C5 activation efficiently inhibited complement activation. In conclusion, CD59 is essential for protecting human NT2‐N neurons against complement‐mediated damage, which is known to occur in a number of clinical conditions including stroke.