In vitro evaluation of canine leukocytes radiolabeled in whole blood with ^9^9^mTc stannous colloid
Introduction: Technetium-99m stannous colloid (^9^9^mTcSnC)-labeled leukocytes are used to investigate a variety of inflammatory diseases in human medicine. The present study investigates the in vitro behavior of canine leukocytes labeled in whole blood with ^9^9^mTcSnC. Methods: Blood samples from 10 healthy dogs were labeled with ^9^9^mTcSnC using a standard procedure. The distribution of radioactivity among blood components (plasma, leukocyte layers and erythrocytes) was measured following separation of the radiolabeled samples across Histopaque density gradients. Phagocytic function of labeled and unlabeled leukocytes was estimated using zymosan particles. Labeling retention by leukocytes was determined at 1, 3, 4 and 7 h postlabeling. Results: The mean+/-standard error percentage of radioactivity associated with plasma, erythrocyte and leukocyte fractions was 2.0+/-0.21%, 55.5+/-0.60% and 42.5+/-0.54%, respectively (the last comprising 70.2+/-0.83% in polymorphonuclear leukocytes and 29.8+/-0.83% in mononuclear leukocytes). Labeled canine leukocytes had a phagocytic activity of 91.3+/-0.28% (control, 91.7+/-0.26%). The radiolabeled canine leukocytes retained 94.1+/-0.30% of radioactivity at 7 h postlabeling. Conclusions: Radiolabeling of canine leukocytes in whole blood with ^9^9^mTcSnC has minor adverse effect on their phagocytic function. The radiolabeled canine leukocytes retained a large percentage of radioactivity for at least 7 h postlabeling.
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