Human killer cells and natural killer cells: distinct subpopulations of Fc receptor-bearing lymphocytes.

Unstimulated human peripheral blood lymphocytes were depleted of K cells, which mediate antibody-dependent cellular cytotoxicity (ADCC) without removing NK cells, which mediate natural killing (NK). K cell depletion was achieved by buoyant centrifugation removal of lymphocytes that bound to glutaraldehyde-treated P815-AB cells at high lymphocyte-to-target ratios. Likewise, NK cells were removed with glutaraldehyde-treated K562 cells without removing K cells. Furthermore, both cytotoxic cell populations were observed directly in one agarose single-cell cytotoxic assay (ASCA) using P815-AB and K562 cells simultaneously as target cells. Moreover, the percentage of total cytotoxic cells was equal to the sum of the percentage of K and NK cells observed in separate ASCA. Collectively, these results indicate that K cells and NK cells are distinct subsets of FcR-bearing lymphocytes. One subset, K cells, has more avid Fc receptors (fcR) than NK cells and are 'activated' via thier FcR to kill antibody-coated target cells. The second subset, NK cells, have less avid FcR and are not 'activated' through their FcR to kill antibody-coated target cells.