Bone accumulation of 99mTc-labeled leucocytes.

Leucocytes were separated from rats' blood by dextran sedimentation method and labeled with 99mTc-pertechnetate. A maximum labeling efficiency of 18.5% was achieved with the addition of 1 mg of stannous chloride. The labeled leucocytes were intact and viable and the 99mTc label was firm. Distribution studies in rats, 3 hr after injection of 99mTc-labeled leucocytes, showed 33% concentration in the mineral part of the bone, this being slightly lower than the 36.8% concentration in the liver. Technetium concentration in the bones due to a complex formed by various ingredients used for leucocyte labeling was excluded since negligible bone uptake was noted after injection of an incubated mixture of 99mTc and all ingredients except leucocytes. Also 51Cr-labeled leucocytes showed no localization in the bone. These studies indicate that 99mTc and intact leucocytes form some sort of complex which has an affinity for bone cortex.