A reappraisal of cellular labeling with radiochromium salts.

The present studies demonstrate that, while erythrocytes preferentially bind hexavalent 51Cr, leukocytes bind the trivalent form with equal avidity. Red cells may be saturated with label in contrast to the binding of 51Cr to leukocytes, which may be described by first-order kinetics. Hexavalent label is rapidly reduced in leukocytes in contradistinction to the finding in red cells. The nonreutilization of label by erythrocytes and leukocytes is not due to inappropriate valency but to protein binding of the label. Unlike nonleukemic cells, leukemic leukocytes elute a large fraction of their label. These factors have been largely overlooked in many previous clinical studies using labeled cells, and they are of sufficient quantitative importance to compromise seriously the validity of numerous earlier reports.