Multidrug resistance-1 in T lymphocytes and natural killer cells of adults with idiopathic thrombocytopenic purpura: effect of prednisone treatment.

High P-glycoprotein-mediated multidrug resistance-1 (P-gp/MDR1) activity in lymphocytes from idiopathic thrombocytopenic purpura (ITP) patients may affect disease outcome. ITP treatment includes glucocorticoids that are substrates of P-gp; hence, P-gp functional activity and antigenic expression were assessed by flow cytometry in T and natural killer (NK) cells from ITP patients before and after prednisone therapy. Herein, patients' T and NK cells did not show increased MDR1 functional activity, whereas P-gp antigenic expression was significantly enhanced in both therapy-free and prednisone-treated patients. Prednisone treatment did not significantly modify the function and expression of MDR1 in T and NK cells of ITP patients.