Spontaneous cell-mediated cytotoxicity in humans. Distribution and characterization of the effector cell.

When lymphocytes from healthy donors were tested as effector cells, the cytotoxic activities observed in spontaneous and in antibody-dependent cell-mediated cytotoxicity were positively correlated. However, with lymphocyte preparations obtained from renal patients, a dissociation between the two activities was occasionally observed. Human natural killer cells are lymphocytes, with receptors for the Fc fragment of IgG molecules, but with no surface immunoglobulin. Their cytotoxicity is reduced by the presence of granulocytes or monocytes. After separation of rosetting and non-rosetting cells with AET- (2-aminoethylisothiouronium bromide hydrobromide) or neuraminidase-treated sheep erythrocytes, the majority of the activity was recovered in the non-rosetting fraction, but a portion of it was present consistently in the rosetting cell fraction. Cells in the latter fraction also displayed receptors for the Fc fragment of immunoglobulin G.