Bone marrow alterations in IFN-γ transgenic mice. (A) Tibial bone marrow of a 3-month-old transgenic mouse showing granulomatous lesions (arrows) stained with H&E. The focal lesions were composed of clusters of histiocytes/macrophages (original magnification × 300; Bouin's fixed and paraffin-embedded section). (B) A rib of an 8-month-old transgenic mouse showing a cartilaginous mass in the marrow cavity attached to the cortical bone. Chondrocytes in the mass are degenerative. The mass is covered with a thin osseous layer. (Original magnification × 75; H&E; Bouin's fixed and paraffin-embedded section.)