Complement Biosynthesis in Vitro by Rat Hepatoma Cell Strains

Abstract

Four separate rat hepatoma strains were examined for their capacity to synthesize complement (C). None of the strains synthesized detectable amounts of the first component (C1), and only one strain (7800C₁) produced the fourth component (C4). However, each of the strains synthesized significant amounts of biologically active C2 and C3. Three of the four strains also produced C5 and the natural inhibitor of C1 (C1 INH). Two control rat cell strains (fibroblast and pituitary) did not synthesize any detectable C components. Production of C, studied extensively in 7800C₁ and H₄, was reversibly inhibited by cycloheximide (2 µg/ml) and [¹⁴C] amino acids were incorporated into C2, C3, and C1 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 C3 by H₄, but C2 and C5 production were not affected. These C-producing hepatoma cells may prove useful for studies of the control of C biosynthesis.