To evaluate the effects of high-dose dexamethasone (HDDXM) on the balance of interleukin-18 (IL-18) and its endogenous antagonist IL-18 binding protein (IL-18BP) in ITP patients, IL-18, IL-18BP as well as IFN-g, IL-4 plasma
levels and platelet counts were determined in 17 ITP patients receiving DXM 40 mg/day for four consecutive days and in 24 healthy subjects. Using RT-PCR, the mRNA expression of IL-18, IL-18BP, IFN-g, IL-4, T-box (T-bet) and
GATA-binding protein 3(GATA-3) were studied in all subjects. The in vitro effects of DXM on IL-18BP and IL-18 of
peripheral blood mononuclear cells (PBMCs) were studied by ELISA. HD-DXM administration increased IL-18BP and
reduced IL-18 expression significantly (presulted in a downregulation of IL-18/IL-18BP ratio pof IL-18BP while diminishing IL-18 release from cultures of PBMCs. These results suggest that downregulation of IL-18/IL-18BP might account for its clinical efficacy of HDDXM in active ITP.