BCG infection of IFN-γ −/− causes profound changes in the spleen. (A) Spleens isolated from infected IFN-γ +/+ (top two spleens) or IFN-γ −/− (bottom two spleens) mice 5 weeks after IP administration of BCG show the change in size and color of the organs. Low power view of spleens sections from IFN-γ +/+ (B) or IFN-γ −/− (C) mice. Note that the overall structure of the red and white pulp is intact in IFN-γ +/+ mice, but the normal architecture of infected IFN-γ −/− is completely effaced (photographed using a 10X objective). Higher power views of the spleen show that the white pulp of infected IFN-γ −/− mice is extensively infiltrated by macrophages (E and G), while infected IFN-γ +/+ mice retain the normal arrangement and cellular makeup of the white pulp (D and F). Note that in (E), a small area of lymphocytes remains in the right-hand portion of the white pulp. Lymphocytes gradually disappeared from the spleen. Magnifications: (D) and (E) (20X objective); (F) and (G) (40X objective). The red pulp of infected IFN-γ −/− mice was infiltrated with extramedullary hematopoietic tissue (H). Note the presence of nucleated erythroid cells, cells of the granulocytic series, and megakaryocytes (40X objective). All sections were stained with hematoxylin and eosin (H&E).