Synthesis of C3, C5, C6, C7, C8, and C9 by Human Fibroblasts

We investigated the ability of human fibroblasts to produce the components of the final common pathway (C3‐C9) of complement in vitro by co‐culturing an alternative complement activator (agarose beads) with the cells. The test system involved incubation of beads with anti‐complement antibodies followed by radioactive‐labelled anti‐Ig detection antibodies. Subsequently, the beads were examined in a radioimmunoassay. Our results indicate that human fibroblasts produce C3, C5, C6, C7, C8, and C9. A neoepitope selectively expressed on activated C9 was detected, indicating assembly of the terminal complement complex and thus formation of a functional terminal complement pathway by the fibroblasts.