An assay for C1q biosynthesis in cultured human fibroblasts

With a standard C1 haemolytic assay, cultured human fibroblasts were shown to synthesize and secrete haemolytically active C1 and C1q. A radioimmunoassay for detection and quantitation of intra-cellular biosynthesis and secretion of C1q was then developed, using Sepharose beads covalently coated with goat monospecific anti-C1q IgG. The fibroblasts were labelled with tritiated amino acids. The molecular structure of fibroblast C1q was found to be unusual in 2 ways: firstly, it probably represented an enlarged pro-C1q, and secondly, the secreted molecule had a different structure from the cell associated molecule. (Auth.)