Mechanism of Antibody-Dependent Natural Killer Cell-Mediated AK-5 Tumor Cell Death

The mechanism of antibody-dependent natural killer (NK) cell-mediated killing of a histiocytic tumor, AK-5, was studied. In vitro exposure of immune NK cells with antibody-primed AK-5 cells induced the formation of stable NK-AK-5 conjugates. The frequency of conjugate formation after 1 h coculture of immune NK cells was severalfold higher than that of normal cells. The occurrence of conjugate formation and the disintegration of conjugated targets only in the presence of anti-AK-5 antibody revealed the antibody dependence in recognition, conjugate formation, and triggering of lytic machinery leading to AK-5 cell death. Coculture of immune NK cells with AK-5 cells in the presence of anti-AK-5 antibody induced the expression of perforin mRNA as well as accumulation of protein in the NK cells and extensive fragmentation of AK-5 cell DNA, thereby indicating the involvement of necrosis and apoptosis in the AK-5 cell death. The antibody-dependent expression of perforin as well as DNA fragmentation indicated these events to be consequent to E-T conjugate formation. The observation of target cell DNA fragmentation revealed that the internal target disintegration is the first event which is followed by membrane damage leading to efficient tumor destruction by the host immune system.