CONTACT-INDUCED CYTOTOXICITY BY LYMPHOID CELLS CONTAINING FOREIGN ISOANTIGENS.

In tissue culture, immune lymph node cells containing foreign histocompatibility antigens of the H-2 type exert marked cytotoxic effects on tumor cells incompatible with the H-2 antigen. An equally pronounced effect is obtained when normal allogeneic and semi-isologous lymphoid cells of F(1) hybrids are caused to aggregate around the target tumor cells by treating the cultures with either heat-inactivated rabbit antiserum to mouse cells or phytohemagglutinin. Isologous lymph node cells have no effect. Thus, aggregation of lymphoid cells and target cells is a necessary but insufficient requirement for cytotoxicity in vitro; in addition, close contact must be established between histoincompatible cells.