Whole blood (200 µl) was stained with Hoechst 33342 (Sigma Aldrich) to label the DNA of leukocytes. Hoechst (5 µg ml−1) was added at 1:100 (v/v) to the sample and incubated for 30 minutes at room temperature in the dark. Subsequently, the sample was washed three times in Phosphate Buffered Saline (PBS; CaCl2-free and MgSO4-free; Invitrogen) with 2% heat-inactivated fetal bovine serum (FBS). After the last wash, the supernatant was replaced with PBS containing 0.2% PluronicTM F-127 (Invitrogen) at 1:1 (v/v) ratio with the packed blood cells to obtain the similar hematocrit as whole blood.