Isolation and labelling of human leukocytes with 99mTc

The role of the leukocyte isolation procedure on cell labelling with ^99mTc has been evaluated. Separation of leukocytes was performed by two procedures: (1) sedimentation on methyl cellulose, followed by discontinuous gradient centrifugation; (2) methyl cellulose sedimentation and hypotonic haemolysis of residual red blood cells. After washing the cells in saline and incubation with a stannous pyrophosphate agent, the leukocytes were labelled with 5–10 mCi ^99mTc. Procedure 1 gave a higher purity but lower recovery of polymorphonuclear leukocytes, and a minor contamination of red blood cells. ^99mTc labelling of cells was slightly more efficient with this method, probably due to the presence of red blood cells. Procedure 1 is recommended for in vitro studies on cell kinetics and procedure 2 is recommended for clinical use.