Regulation of synthesis of complement proteins in HEp2 cells.

We investigated the synthesis of complement proteins in HEp2 cells and its regulation. Using metabolic labeling with [35S]methionine, immunoprecipitation, and SDS-PAGE, we demonstrated that HEp2 cells synthesized C1r, C1s, C1 inhibitor, C3, C4, factor B, and factor H. The constitutive synthesis of C1r and C1s were the highest among these proteins, whereas the synthesis of C4 was observed only when the cells were stimulated with IFN-gamma. C1r and C1s were secreted readily, whereas the rate of the secretion of C4 and C1 inhibitor was much slower. Activated forms of C1r, C1s, and complexes of C1 inhibitor--C1s were found. IL-1 and TNF induced 6- and 7-fold increases in the synthesis of C3 and factor B. IFN-gamma induced increases in the synthesis of all seven proteins, the most pronounced effects being on the synthesis of C4 and C1 inhibitor--15- and 44-fold, respectively.