Visualization of surface topology of human lymphoid cells by scanning electron microscopy

We have studied the surface characteristics of human lymphoid cells with the scanning electron microscope (SEM). We obtained thymic cells by mincing thymus and isolating peripheral blood lymphocytes from normal donors as well as patients with acute and chronic lymphocytic leukemia (ALL and CLL). Prior to SEM, we purified the lymphocytes in isoosmotic Ficoll-Hypaque gradients. In addition, we examined several lymphoid cell lines in permanent culture derived from normal persons, patients with infectious mononucleosis, as well as from patients with ALL. The surfaces of most thymic cells appear smooth with only a few short microvilli. A small number of thymic cells, on the other hand, are found to exhibit many more microvilli of uniform shape and length. We could further identify lymphocytes from normal donors as T- and B-types according to their rosetting spontaneously with sheep red blood cells (SRBC) resemble thymic cells in their surface topology. However, B-cells rosetting with amboceptor--and complement--treated SRBC show greater number of microvilli. The surface morphology of lymphocytes from leukemic patients appears more or less characteristic of the disease type. In contrast, the surfaces of cultured lymphoid cells show a diversified surface topology, often with large smooth areas, very long and very short microcilli, which may often cluster in groups. These data bear directly upon techniques of plasma membrane fractionation and we suspect that the topology differences correlate with their differentiation patterns.