Spleen cells from BALB/c mice bearing a syngeneic mammary
adenocarcinoma nonspecifically destroy xenogeneic targets following in vitro induction with mammary
tumor-associated
antigens. Studies were undertaken to characterize the effector cell population(s) mediating this "innocent bystander" cytotoxicity reaction. Fractionation experiments using phagocyte-depleted spleen cells revealed that the effector population was adherent to
nylon wool columns. Flow cytometric analysis of the
nylon-adherent cells revealed the presence of a minor population of Thy 1.2+ cells. Following treatment of the
nylon-adherent cells with anti-Thy 1.2 and
complement, the cytotoxic activity was abolished. Furthermore, when those cells expressing the
Thy 1.2 antigen were positively selected by cell sorting, they were able to mediate the cytotoxic reaction. In contrast,
nylon-adherent Thy 1.2-negative cells were unable to mediate the reaction following selection by cell sorting. Depletion studies with anti-Lyt 1 or anti-Lyt 2 and
complement also abolished this cytotoxic response. Additional studies demonstrated that
nylon-adherent spleen cells from mammary
tumor-bearing mice were not able to lyse natural killer cell-sensitive targets. These data suggest that the cells which effect
tumor antigen-induced "innocent bystander" cytotoxicity, or their activated precursors, are
nylon-adherent Thy 1.2+, Lyt 1+2+ T-cells.