TABLE 3.

iNOS and 2,3-IDO activities in primary murine lung cells from NOS2^−/− and NOS2^+/+ mice^a

Mice	Treatment	Nitrite (μM/ml)b
NOS2−/−	None	0.56
	l-NMMA	0.64
	IFN-γ + LPS	1.15
	IFN-γ + LPS + l-NMMA	1.05
NOS2+/+	None	0.64
	l-NMMA	0.67
	IFN-γ + LPS	46.8
	IFN-γ + LPS + l-NMMA	12.1

^a2,3-IDO activity was assessed by quantifying accumulated tryptophan catabolites in culture supernatants (6), and no activity was found. 

^biNOS activity was assessed by measuring nitrite accumulation using the Greiss reaction as described previously (33).