Leukocyte Labeling with 51Chromium

Abstract

Abstract A method for labeling concentrated leukocytes in vitro with radioactive chromium is described. Intravascular survival data and organ distribution of the 51Cr-labeled leukocytes of ten hematologically normal subjects are presented and compared with the results of sequential or simultaneous granulocyte survival determinations using 32DFP. Both granulocytes and lymphocytes are labeled by 51Cr. No evidence of diminished cell viability or significant elution or reutilization of the label could be demonstrated by in vitro studies. Curves of both 51Cr and 32DFP leukocyte radioactivity in the circulation were exponential, with average T 1/2 values of 10.5 and 10.3 hours respectively, reflecting the random departure of labeled granulocytes from the circulation. An early rapid phase of label disappearance was noted in the 51Cr studies, attributable to label elution or the disappearance of labeled non-granulocytic leukocytes. Body counting rate curves during the first 12 hours parallel the disappearance of leukocyte and plasma radioactivity; a later plateau reflects radioactivity in RBC contaminating the concentrated leukocyte suspensions. No evidence of pulmonary or splenic sequestration was noted. Estimations of granulocytic pool sizes from the 51Cr data compared poorly with data derived using 32DFP, probably as a result of the early elution of a portion of the radiochromate from the labeled cells or from the more rapid disappearance of 51Cr-labeled mononuclear cells. Epinephrine infusion after injection of labeled leukocytes produced peripheral leukocytosis, increased counting rates over the lungs, liver and heart and a marked diminution in counting rates over the spleen suggesting that a significant portion of the marginal granulocytic pool is located in the spleen. We conclude that the 51Cr labeling technic will be useful in the study of the intravascular survival and tissue distribution of cells not labeled with 32DFP, and that its use will supplement the study of granulocytes labeled with 32DFP.