Mechanisms of Corticosteroid Action in Immune Thrombocytopenic Purpura

To determine the mechanism by which platelet counts increase after corticosteroid therapy for human immune thrombocytopenic purpura (ITP), we studied the platelet kinetics using prednisolone (PDN)-treated ITP-prone mice, (NZW x BXSB) F, (W/B F,). An increase in platelet counts was observed in W/B F, mice (n = 10, mean f SD, 1,202 f 202 x 103/pL) 4 weeks after treatment with PDN (2 mg/ kg/d); no increase occurred in nontreated W/B F, mice (n = 5,651 f 126, P < .005). Prolonged platelet life-spans (PLSs) were observed in treated W/B F, mice (1.29 f 0.40 days), but not in nontreated controls (0.60 f 0.24 days, P < .Ol). No increase in platelet production (platelet turnover) was found in PDN-treated W/B F, mice, but significant decreases in platelet-associated antibodies (PAAs) and platelet-bindable serum antibodies (PBAs) were noted. Studies on organ