Phenotypic characteristics of human natural killer cells

Surface antigen analysis of human natural killer (NK) cells using anti-lymphocyte monoclonal antibodies identifies NK cells as a discrete cell type (average 15% of peripheral blood lymphocytes) distinct from T, B, and myelomonocytic cells. Virtually all NK cells bear low-affinity Fc receptors for IgG, as detected by antibody B73.1 and N901 antigen; 80-90% of NK cells express the E receptor (OKT11), the C3bi receptor (OKM1), and the T10 antigen; 30-50% are T8 (+), and 30-70% are Leu7 (+). This phenotype is maintained on NK cell-derived clones and on activated NK cells, which are induced to express interleukin 2 receptor (Tac antigen), transferrin receptor, HLA-DR, and several T cell activation antigens but not, like resting NK cells, antigens (T1, T3, T4) characteristic of T cells. On the contrary, NK cell-derived leukemias may express T1 or, more frequently, T3 antigens.