Peripheral localization and distinct morphology of Gr1+ cells present in necrotic lungs.
Anti-Gr1 immunohistochemistry was performed to determine the location of Gr1+ cells surrounding necrotic lesions in the NOS2 -/- mice. As observed in low magnification (4x), anti-Gr1 labeling was predominantly localized in the periphery or rim of these structures (red, arrows, A). At higher magnification (100x), two distinct cellular morphologies could be observed for cells staining with anti-Gr1. In the left panel, neutrophils with multi-lobed nucleus could readily be seen. However, particularly in close apposition to the fibrotic capsule, cells were seen that had abundant and vacuolated cytoplasms as well as a unilobed nucleus, consistent with the morphology of MDSCs. Arginase activity was biochemically detected in the lungs of NOS2 -/- mice but minimally WT controls (B). As disease progressed in NOS2 -/-, more arginase activity could be detected compared to wild-type mice (B).Results are expressed as the mean values of arginase activity (± SEM, n=5) in the Lung. **Student t-test, p<0.01 and ***Student t-test, p<0.001. Anti-arginase-1 immunohistochemistry was performed to determine its expression by inflammatory cells in the lungs of NOS2-/- mice. Similar to the anti-Gr1 staining, at low magnification (4x), robust arginase-1 expression was detected in cells located in the rim of necrotic granulomas (C, left panel). At higher magnification (100x), arginase-1 expression was limited to highly vacuolated cells containing abundant cytoplasm (C, right panel). Panel D shows co-localized staining of both Gr1+ and arginase-1 in NOS2 -/- mouse lung tissues after 45 days of infection. At higher magnification (100x), co-localized staining of Gr1+ and arginase-1 demonstrates that Gr1+ cells (D lower right panel, arrow, red) and arginase-1 staining (D, arrow, brown) are clearly co-localized on the same cell.