MONONUCLEAR CELL IN HUMAN-BLOOD WHICH MEDIATES ANTIBODY-DEPENDENT CELLULAR CYTOTOXICITY TO VIRUS-INFECTED TARGET-CELLS .2. IDENTIFICATION AS A K CELL

Abstract

Studies were done to determine whether the mononuclear cell in human blood which mediates antibody-dependent cellular cytotoxicity (ADCC) to herpes simplex virus (HSV)-infected target [human Chang liver] cells has surface Fc receptors which participate in the reaction. The F(ab'')2 fragment of human Ig[immunoglobulin]G antibody was inactive in ADCC and in complement-mediated cytolysis, but retained the capacity to neutralize infectious virus, to agglutinate erythrocytes coated with viral antigens and to bind to the surface of virus-infected cells. Treatment of sensitized virus-infected target cells with Staphylococcus protein A, which has affinity for the Fc epitope of IgG, strongly reduced their susceptibility to lysis by ADCC in a dose-dependent relationship. The Fc portion of IgG antibody to the virus is apparently necessary for cytotoxicity. Treatment of blood mononuclear cells with heat-aggregated .gamma.-globulin or HSV immune complexes inhibited effector cell activity. The presence of 3rd party cellular immune complexes strongly inhibited ADCC. Adsorption of mononuclear cells to plastic surfaces coated with soluble 3rd party immune complexes resulted in a significant reduction in effector cell activity. The ADCC effector cell possesses surface Fc receptors which are utilized in the ADCC reaction. The presence of Fc receptors on the surface of the effector cell indicates that it is a K cell rather than a null cell.