Extended Data Figure 9: Secretion of C4, and specificity of the monoclonal anti-C4 antibody for C4 protein in human brain tissue and cultured primary cortical neurons.

a, Brain tissue (from an individual affected with schizophrenia) was stained with a fluorescent secondary antibody, C4 antibody, or C4 antibody that was pre-adsorbed with purified C4 protein. Confocal images demonstrate the loss of immunoreactivity in the secondary-only and pre-adsorbed conditions. b, Primary human neurons were stained with a fluorescent secondary antibody, C4 antibody or C4 antibody that was pre-adsorbed with purified C4 protein. Confocal images demonstrate the loss of immunoreactivity in the secondary-only and pre-adsorbed conditions. Scale bars, 25 μm. c, Secretion of C4 protein by cultured primary neurons. Western blot for C4 protein analysis. (+) Purified human C4 protein. (–) Unconditioned medium, a negative control. HN-conditioned shows the same medium after conditioning by cultured human neurons at days 7 (d7) and 30 (d30). Details of western blot protocol, antibody catalogue numbers and concentrations used are in Supplementary Methods. C4 molecular weight, ~210 kDa.