Complement biosynthesis in vitro by rat hepatoma cell strains

Four separate rat hepatoma strains were examined for their capacity to synthesize complement (C). None of the strains synthesized detectable amounts of the first components (C-1), and only one strain (7800C-1) produced the fourth component (C4). However, each of the strains synthesized significant amounts of biologically active C-2 and C-3. Three of the four strains also produced C-5 and the natural inhibitor of C-1 (C1 INH). Two control rat cell strains (fibroblast and pituitary) did not synthesize any detectable C components. Production of C, studied extensively in 7800C-1 and H-4, was reversibly inhibited by cycloheximide (2 mug/ml) and [ 14-C ] amino acids were incorporated into C-2, C-3, and C-1 INH. As assessed by gel filtration, the elution positions of the C components synthesized by the cells in culture were similar to those of the corresponding proteins in normal rat serum. Hydrocortisone (10-6 to 10-7 M) stimulated the production of C-3 by H-4 but C-2 and C-5 production were not affected. These C-producing hepatoma cells may prove useful for studies of the control of C biosynthesis.