Activated murine peritoneal macrophage cytotoxicity against P815 tumor
cells has been shown to be mediated by the reactive nitrogen intermed
iates (RNI) produced by macrophages from L-arginine through nitric oxi
de (NO) synthase. Previous results from this laboratory indicated that
NO-dependent killing of P815 fulfilled the criteria for apoptotic dea
th. Work by others, in turn, demonstrated that the product of the bcl-
2 gene confers protection against various inducers of apoptosis, inclu
ding reactive oxygen intermediates. Experiments were performed to dete
rmine whether Bcl-2 could equally protect sensitive cells from RNI-dep
endent apoptosis within the context of a relevant biologic system such
as the delivery of such RNI by activated macrophages. Results demonst
rated that transfection of P815 cells with the human bcl-2 gene confer
s immunity from RNI-dependent, macrophage-mediated cytotoxicity. In co
ntrast with wild-type or mock-transfected P815 cells, which do not con
tain detectable Bcl-2, bcl-2-transfected cells showed minimal DNA frag
mentation and cell membrane failure when cocultured with activated mac
rophages. Additional findings indicate that Bcl-2 affords the transfec
ted cells almost complete resistance to the DNA-fragmenting effects of
chemically generated NO or H2O2, and partial protection from their cy
tolytic effects. These findings are consistent with the hypothesis tha
t tumor cells expressing bcl-2 may escape destruction by macrophage-de
pendent immune surveillance mechanisms.