Kn. Dileepan et al., DIRECT ACTIVATION OF MURINE PERITONEAL-MACROPHAGES FOR NITRIC-OXIDE PRODUCTION AND TUMOR-CELL KILLING BY INTERFERON-GAMMA, Journal of interferon & cytokine research, 15(5), 1995, pp. 387-394
Interferon-gamma (IFN-gamma) is known to prime macrophages for tumor c
ell lysis and nitric oxide (NO) production as measured by enhanced sen
sitivity to lipopolysaccharide (LPS). In the present study, the abilit
y of IFN-gamma to directly activate peritoneal macrophages from C57BL/
6 and Balb/c mice for tumor cytotoxicity and NO production was evaluat
ed. Macrophage-mediated tumor cell killing was measured by an 18 h Cr-
51 release assay using P815 mastocytoma cells as targets. Concurrent N
O production was measured as nitrite in the supernatants of macrophage
cultures. Incubation of macrophages with IFN-gamma resulted in activa
tion of macrophages for tumor cell lysis. IFN-gamma alone also activat
ed macrophages for NO production under identical conditions. Addition
of LPS along with IFN-gamma resulted in synergism in the activation of
macrophages for both cytolysis and NO production. LPS contamination o
f the IFN-gamma preparation was absent as evidenced by the following c
riteria: (1) the IFN-gamma preparation as well as the reagents used we
re shown to be free of LPS contamination based on LAL endotoxin tests
(sensitivity 25 pg/ml), (2) the ability of IFN-gamma to activate macro
phages was not abrogated by prior treatment of the cytokine with polym
yxin B, whereas the effect of LPS was inhibited (70-100%) under simila
r conditions, (3) pretreatment of the IFN-gamma preparation with a spe
cific endotoxin neutralizing protein did not abrogate the ability of I
FN-gamma to induce macrophage activation, and (4) heat treatment of so
lutions containing IFN-gamma alone or IFN-gamma + LPS abolished only t
he effect of IFN-gamma, not that of LPS. A comparison of the IFN-gamma
responsiveness in the peritoneal macrophages from C57BL/6 and Balb/c
macrophages revealed that C57BL/6 macrophages are more responsive to I
FN-gamma. These results demonstrate that IFN-gamma alone is capable of
stimulating macrophages for tumor cell killing and NO production and
that the magnitude of IFN-gamma responsiveness varies with the strain
of mice studied.