Effect of patient sera on IL-6–induced hepcidin expression in PLC/PRF/5 cells. (A) Dose required for response of hepcidin mRNA expression to IL-6 was determined in PLC/PRF/5 cells grown in medium containing IL-6 at final concentrations of 0.001, 0.01, 0.1, 1, 10, and 100 ng/mL. IL-6 at 0.1 to 10 ng/mL, but not at 0.001 to 0.01 ng/mL, increases the expression of hepcidin in a dose-dependent manner. (B) Hepcidin mRNA expression in PLC/PRF/5 cells treated with culture medium containing 10% of either fetal calf serum, serum from healthy volunteers (n = 3), or serum from MCD patients (n = 8). Cells stimulated with IL-6 (10 ng/mL) showed an approximately 8-fold increase in hepcidin mRNA expression compared with nonstimulated controls. Serum from patients A, B, C, E, F, and H enhanced IL-6–induced hepcidin expression (13- to 22-fold), whereas serum from patients D and G and serum from 3 healthy volunteers had no such effect on IL-6–induced hepcidin expression (6- to 8-fold increase).