Activation of murine macrophages (M phi) requires the collaboration of sign
als derived from the immune system and the environment. In this study, we e
ngineered a murine M phi cell line to become activated in response to an en
vironmental signal, hypoxia, as the sole stimulus. Hypoxia is a condition o
f low oxygen tension, occurring in several pathological tissues, which acts
in synergy with IFN-gamma to induce full M phi activation. We transfected
the ANA-1 murine M phi cell line with a construct containing the IFN-gamma
gene controlled by a synthetic promoter inducible by hypoxia (HRE3x-Tk), an
d we characterized the cellular and molecular biology of the engineered M p
hi under normoxia or hypoxia. Engineered M phi in normoxia expressed basal
levels of IFN-gamma mRNA and protein that were strongly augmented by shifti
ng the cells to hypoxia. Furthermore, they responded to the synthesized IFN
-gamma with induction of IFN-responsive factor-1 and 2'-5'-oligoadenylate s
ynthase expression. Under normoxic conditions, the engineered M phi had a s
ignificant constitutive level of la Ags and Fc receptors. Hypoxia induced f
urther augmentation of Ia and Fe expression. Finally, hypoxia induced induc
ible NO synthase expression, and subsequent reoxygenation led to the produc
tion of NO. In conclusion, the engineered M phi, which produce IFN-gamma in
an inducible manner, express new biochemical and functional properties in
response to low oxygen environment as the sole stimulus, thereby circumvent
ing the need for costimulation by other immune system-derived signals.