Ferritin synthesis by cytokine-treated macrophage J774 cells. J774 cells untreated or treated with IFN-γ/LPS for 24 hours were incubated in the presence of ³⁵S methionine plus cysteine (TRAN³⁵S-LABEL) for 2 hours. Equal amounts of labeled proteins were then immunoprecipitated with antibodies against recombinant mouse H and L ferritin subunits (lanes 3 and 4); an aliquot of the supernatants containing total proteins was also loaded on the gel (lanes 1 and 2). Total proteins and immunoprecipitated ferritin chains were separated on 15% SDS/polyacrylamide gels and visualized by fluorography. The results shown are representative of four separate experiments.