THE PRESENCE OF LIPID DROPLETS AND THE ABSENCE OF STABLE SUDANOPHILIA IN OSMIUM-FIXED HUMAN LEUKOCYTES

In blood smears fixed in osmium vapor and stained with Sudan black B or oil red O, neutrophil and eosinophil leukocytes contain a regular number of sudanophilic granules and do not exhibit stable sudanophilia. Stable sudanophilia occurs following aldehyde fixation without the appearance of sudanophilic granules in white cells. The sudanophilia in granules was lysochromic since the granules could be reversibly decolorized by dye solvents. Cold acetone extracted the content of the granules following osmium tetroxide oxidation. Electron microscopically the granules had the appearance of typical lipid droplets. Human granulocytes thus contain a constant amount of free lipid deposits that are adequately preserved only by osmium tetroxide fixation. Osmium seems to prevent the occurrence of stable sudanophilia through inhibition of myeloperoxidase activity. The procedure may be useful to follow variations of lipid content in human leukocytes, as exemplified by the excess of lipid found in leukocytes, in synovial fluids of patients with rheumatoid arthritis.