Effect of LPS/IFN-γ on IRP activity in monocytes from GH patients. Monocytes of GH patients were incubated for 4, 8, and 24 hours in the presence (A) and in absence (B) of cytokines (100 U/mL IFN-γ + 1 μg/mL LPS). Monocytes of control subjects (C), patients with GH, and secondary hemochromatosis (SH) were treated with LPS/IFN-γ for 24 hours (C). IRP activity and TNF-α were determined as described in Fig 1. IRP activity in monocytes from patients with GH rose transiently 4 hours after stimulation with LPS/IFN-γ but was not downregulated at 24 hours. On the contrary, in cells from SH patients IRP downregulation was observed at 24 hours.