The expression levels of mRNAs for MDR1 (P-glycoprotein), multidrug resistance-associated proteins (MRP1), and BCRP (breast cancer resistance protein; mitoxantrone resistance protein) were quantitatively determined in lymphocytes and monocytes. Monocytes and lymphocytes were obtained from 3 healthy male and 2 healthy female volunteers. BCRP, MDR1, and MRP1 mRNA levels were determined by real-time quantitative reverse transcriptase polymerase chain reaction. In lymphocytes, relative concentrations of mRNAs for target proteins (BCRP, MDR1, and MRP1) were 1.00 +/- 0.478, 9.67 +/- 5.53, and 0.116 +/- 0.0613 respectively, and in monocytes 1.00 +/- 0.854, 0.821 +/- 0.263, and 0.090 +/- 0.052, respectively. The MDR1 mRNA level was cell type dependent, whereas there was no difference in BCRP and MRP1 expression levels between lymphocytes and monocytes. Comparison of mRNA levels for the three major multidrug-resistant efflux pumps reveals that MDR1 is the predominant form in lymphocytes and BCRP is the predominant form in monocytes. 2007 S. Karger AG, Basel PMID: 17911978 [PubMed - indexed for MEDLINE]