SELECTIVE FLUORESCENCE REACTION OF INDIGOCARMINE STAINED EOSINOPHIL LEUKOCYTE GRANULES INDUCED BY ALKALINE REDUCTION OF THE BOUND DYE TO ITS LEUCO DERIVATIVE

After staining of mammalian blood smears with indigocarmine, eosinophi l granules were the unique cell components which stained deeply blue u nder bright field illumination. Treatment of stained smears with the r educing agent sodium borohydride completely abolished this colour reac tion, while under violet-blue exciting light eosinophil granules appea red with bright green fluorescence. Other reducing agents proved less suitable. Spectral analysis of indigocarmine solutions reduced by sodi um borohydride showed an emission peak at lambda = 528 nm and confirme d the microscopic observations. These results indicate that the treatm ent of indigocarmine stained structures with alkaline solutions of str ong reducing agents converts the bound dye into its reduced and highly fluorescent leuco derivative.