Ultrastructure of CD57+ cells isolated from human tonsils or blood.

The presence of CD4+, CD57+ T cells in the germinal centers has been reported by several authors. The CD57 antigen is also expressed by natural killer (NK) cells. We purified CD57+ cells from human tonsils and blood by microdissection, rosetting with sheep red blood cells and magnetic cell sorting (MACS) and examined the ultrastructural morphology of these cells. Clear differences were found in cell aspect: blood NK contained large granules which were not found in the tonsillar CD57+ cells. These latter appeared medium-sized and not fully activated. After immunolabeling, the tonsillar CD57+ cells were mainly found in the light zone of the germinal centers.