Peripheral blood was collected in heparinized tubes in 10 ml samples and placed immediately on ice. Next, 10 ml of 3% dextran 200 000 (WAKO, Osaka, Japan) was added to the tubes, which were than placed in ice for 30 min. The supernatant was collected and centrifuged. The precipitant was dispersed in distilled water to lyse the remaining erythrocytes, and an equal volume of 1.8% NaCl was then immediately added. The isolated cells were washed, then centrifuged. Total RNA was extracted following standard procedures (Chomczynski and Sacchi, 1987) and resolved in 20 µl of distilled water, then stored at -70˚C.