The importance of radiolabelling human granulocytes with 111In-tropolonate or 111In-2-mercaptopyridine-N-oxide in plasma containing acid-citrate-dextrose.

When blood cells are radiolabelled in plasma, for example with 111In-tropolonate, the plasma always contains an anticoagulant, usually acid-citrate-dextrose (ACD) or heparin. The effect of ACD and heparin on the labelling efficiency (LE) and optimum concentration of ligand required to radiolabel human granulocytes in plasma with 111In-tropolonate or 111In-2-mercaptopyridine-N-oxide (111In-merc) has been measured. The concentrations of ligand (tropolone or merc) required for maximum cell labelling in plasma containing ACD were 4 X 10(-4) M tropolone and 1 X 10(-4) M merc, whereas using plasma containing heparin, the optimum concentrations were 10-fold higher, at 4 X 10(-3) M and 1 X 10(-3) M respectively. At the optimum ligand concentrations, the LE for 1 X 10(8) granulocytes labelled in plasma containing ACD was 90% using 111In-tropolonate and 82% using 111In-merc, whereas using plasma containing heparin they were 68% and only 20%, respectively. Addition of ACD to heparinised plasma abolished the necessity for more ligand and increased the LE to the same values as those for plasma containing ACD alone. These results clearly demonstrate that to obtain a high LE using the lowest possible concentrations of tropolone or merc, the granulocytes must be labelled in plasma containing ACD.