LABELING OF LEUKOCYTES WITH TC-99M EXAMETAZIME CAUSES IN-VITRO UP-REGULATION OF GRANULOCYTE CD11B WITHOUT CORRELATION TO TISSUE UPTAKE IN-VIVO

The aims of this study were to investigate whether labelling with tech netium-99m exametazime alters the expression of adhesion molecule CD11 b on granulocytes and monocytes, and to study whether the expression o f CD11b on unlabelled or labelled cells correlates with uptake of the labelled cells in the inflamed bowel, in the lungs or in the reticuloe ndothelial system. Leucocytes were obtained from 25 patients with infl ammatory bowel disease who underwent leucocyte scan. The cellular expr ession of CD11b was analysed using flow cytometry. Labelling with Tc-9 9m-exametazime induced an increased surface expression of CD11b on gra nulocytes (P < 0.01), but not on monocytes. The increase in CD11b expr ession on granulocytes was lower than the spontaneous mobilization tha t occurred at 37 degrees C and correlated neither with this, nor with N-formyl-methionyl-phenylalanine induced expression of the same recept or. Basal expression of CD11b on unlabelled granulocytes, but not on m onocytes, correlated with bowel and lung uptake 45 min after reinjecti on of labelled cells, but not with uptake on later images. No correlat ion was found between the CD11b expression on labelled granulocytes or monocytes and scintigraphic uptake. Our findings show that labelling with Tc-99m-exametazime increases the expression of adhesion protein C D11b on granulocytes. The increase in surface expression of CD11b does not correlate with the scintigraphic uptake of labelled cells in the bowel, in the lungs or in the reticuloendothelial system.