Immunohistochemical staining of P-gp (A and B) and correlation of P-gp levels and MDR1 mRNA levels in AML patients (C and D). Examples of immunostaining using anti-P-gp antibody Ab-1 are shown in (A) and (B). A large portion of cancer cells were stained for P-gp in Pt. 7 (A) and a small portion of cancer cells in Pt. 2 (B) (original magnification × 400). Some of cells positively immunostained for P-gp were indicated by arrows. Immunohistochemical analysis was performed on many other patients with both anti–P-gp antibody Ab-1 (C) and MRK-16 (D). Correlations between P-gp levels by immunohistochemical analysis and MDR1 mRNA levels by RT-PCR are shown in (C) and (D). Dashed line indicates cut-off point ofMDR1 mRNA expression.