FROZEN-SECTION MICROAUTORADIOGRAPHY IN THE STUDY OF RADIONUCLIDE TARGETING - APPLICATION TO INDIUM-111-OXINE-LABELED LEUKOCYTES

The microscopic biodistribution of radioactivity in tissues is importa nt in determining microdosimetry. This study addresses the use of froz en section microautoradiography in studying the subcellular distributi on of In-111 in leukocytes labeled with In-111-oxine. Methods: In conj unction with frozen section microautoradiography, computer image analy sis methods were applied to the analysis and quantification of leukocy te sections and superimposed autoradiographs. Rapid cell fractionation was used to confirm the results. Results: The emulsion (Ilford K2) re sponse was linear over the concentration range investigated (0-33 MBq ml(-1)). Resolution of radionuclide distribution was better than 2 mu m. The autoradiographs showed no dependence of radiolabel uptake on ce ll type. Classification of all cells into intervals according to grain density suggests an exponential rather than normal distribution, with approximately 50% of cells having little or no radiolabel. In any one sample, cells which were heavily labeled were approximately 10 times more likely to be found in aggregates (60% found in aggregates, mostly neutrophils) than cells which were not heavily labeled (6% found in a ggregates); and the grain densities were at least twofold higher over nuclei than over cytoplasm. The last observation was confirmed by the rapid cell fractionation method which showed that approximately 57% of the total radioactivity was bound to nuclei. Conclusion: Frozen secti on microautoradiography is a practical and reliable approach to determ ining sub-cellular distribution of In-111. The radiolabeling process c auses aggregation of neutrophils. Uptake is not significantly dependen t on cell type, but only a fraction of cells are appreciably labeled. The radioactive concentration in cell nuclei is at least two-fold high er than in cytoplasm. Microautoradiography can be used to provide dist ribution data as input into computer models for sub-cellular dosimetry .