NOS2 and infection: Figure 4D shows co-localized staining of both Gr1+ and arginase-1 in NOS2 -/- mouse lung tissues after 45 days of infection. Co-localized staining of Gr1+ and arginase-1 demonstrates that Gr1+ cells (Figure 4D lower right panel, arrow, red) and arginase-1 staining (Figure 4D, arrow, brown) are clearly co-localized on the same cell.