Immunohistochemistry of IFN-γ. Liver (A,C) and spleen (B,D) sections were obtained at day 7 after syngeneic BMT (A-B) and allogeneic BMT (C-D) and tested for IFN-γ protein by immunohistochemistry as described in “Materials and methods.” Abundant IFN-γ protein was detected with peroxidase staining as brown granules in the spleen (D) but not in the liver (C) after allogeneic BMT. IFN-γ staining was detected in neither liver nor spleen from syngeneic BMT (A-B). Methylgreen counterstain; original magnifications, × 400.