Scanning electron microscopy of normal human peripheral blood cells.

To investigate the surface morphology of peripheral blood cells, venous blood specimens drawn from 16 normal healthy subjects were studied with scanning electron microscopy. Blood cells were fixed with 2% glutaraldehyde and stained with Riu's A and B solutions. Red blood cells, platelets and specific types of leucocytes were identified and photographed through a light microscope. The cells were then fixed with OSO4, dehydrated, dried and metal-coated. Observation with a scanning electron microscope revealed that the erythrocytes were biconcave in shape with smooth surfaces. Adhesion to one another was in rouleaux formation. The surface morphology of the neutrophils was characterized by irregular and branching ridges. Prominent pits on the cell membranes were also noted. A few microvilli, similar to those seen in lymphocytes, were distributed sporadically on the surface. Lymphocytes were much smaller in size than neutrophils. Variable amounts of short upright microvilli, which probably represented the different functional status of the cells, were observed. The monocytes possessed folding cellular processes, while the eosinophils had a villous and granular appearance. Circulating platelets existed in two forms: the native form with discoid shape and the activated form with pseudopodia. The surface was smooth. It is concluded that most peripheral blood cells can be identified by their specific topographic characters. The information thus obtained by scanning electron microscopy can facilitate the cytodiagnosis of abnormal specimens such as sputum, pleural effusion and ascites.