Leucocyte and contaminant cell-bound activities resulting from the labelling of leucocytes with 111In-oxine

A simple method is described for estimating the activities bound to leucocytes, erythrocytes, platelets and the free activity, as resulted from the preparation and labelling of leucocytes with 111In-oxine. Measurements are required only of 111In activity, suspension volumes, and platelet concentrations. The limitations of the method are discussed. When blood from a normal volunteer was labelled by an 111In-oxine manufacturer's recommended technique, the greatest proportion of activity was bound to leucocytes, and in addition, a significant proportion of the activity was found to be associated with platelets. If the number of centrifugations between sedimentation and labelling was reduced from two to one, the proportion of free activity increased at the expense of a reduction in leucocyte activity, but the platelet activity remained unchanged. The relative distribution of cell-bound and free activities was independent of the relative centrifugal force (85–450 g), and of the time (15–30 min) and the suspension volume (5–10 ml) used to incubate the cells with 111In-oxine.