Significant numbers of Gr1<sup>int</sup> CD11b<sup>+</sup> cells were also found in RAG2-/- and C3HeB/FeJ mice.

<p>The influx of Gr1<sup>int</sup>CD11b<sup>+</sup> cells was evaluated in immunocompromised RAG-/- (A), and immunocompetent C3HeB/FeJ mice (C) and NOS-/- (F). Again, large numbers of Gr1<sup>int</sup>CD11b<sup>+</sup> cells were observed in these three mouse strains and significant differences were observed in the Gr1<sup>+</sup> MFI (B, D, G). Similar to NOS2 -/- mice, arginase activity was also increased in C3HeB/FeJ undergoing lung necrosis (E). In contrast, C3H/HeOuJ did not have major arginase activity. Similar to NOS2 -/- mice, arginase activity was also increased in C3HeB/FeJ undergoing lung necrosis (E). Results are expressed as the mean values of mean fluorescence intensity (MFI) or arginase activity (± SEM, n=5) in the Lung. **Student t-test, p<0.001. </p>