Scanning electron microscopy of human leukocytes. A comparison of air dried and critical point dried cells

The present report concerns the comparison of air drying and critical point drying procedures in the preparation of human blood cells for scanning electron microscopy. Normal and leukemic cells obtained from human buffy coats and cultured human leukemic cells grown in suspension culture were studied. Cells were collected by an aspiration filtration technique onto a silver membrane, fixed with glutaraldehyde and osmium tetroxide and never exposed to air at any stage of this procedure or during the subsequent fixation and dehydration. Half the membrane was air dried and the remaining portion dried in carbon dioxide by the critical point drying method, after further dehydration through a graded series of amyl acetate. Comparison of these procedures showed that critical point drying was superior to air drying and enabled one to characterize normal leukocytes and recognize different types of circulating lymphocytes on the basis of their surface architecture. Air drying caused considerable loss of surface detail and did not permit characterization of the different cell types. Multiple microvilli were only evident on the surface of some normal and leukemic lymphocytes and cultured lymphoid cells after critical point drying.