Scanning Electron Microscopy of Human

I t is now generally accepted that two distinct classes of lymphocytes are present in different species including man--thymus-derived (T) cells and bone marrow or bursalderived (B) cells (1, 2). Although similar in appearance these two cell types have been demonstrated to have widely different functions. They can be distinguished electrophoretically by their different mobility (3, 4), serologically by the presence or absence of specific surface antigen markers (5-7), and by their different in vitro reactivity to various lectins (8, 9). B cells are readily recognized by surface immunoglobulin staining (10), the presence of Fc receptors detected by uptake of aggregated 3'globulin (11), and by a complement receptor (12). Recently it has been demonstrated that T cells in the human have the specific property of forming rosettes with sheep red blood cells. This simple procedure is finding wide application for the recognition of T cells (13, 14). Electron microscope observations, utilizing ferritin (15), virus, or peroxidase markers (16, 17), and autoradiography (18) have been used to identify certain of the surface components of B and T cells. However, the distinction between B and T-derived cells has depended so far primarily on these immunologic methods, since by routine light and transmission electron microscopy, these two types of lymphocytes have not been clearly distinguished (14, 19-21).