Figure 4.

Histological analysis of necrotic lesions induced in C57BL/6 mice infected with Mycobacterium avium 25291 for 4 (a–c) or 8 (d) months. Sections were stained with H&E (a) or for acid-fast bacteria (ZN) (b–d). (a) and (b) show the same lesion magnified 28×. (c) provides a higher power view to show the layering at the periphery of the tubercles with an external area of fibrosis, and intermediate layer of heavily infected macrophages and an inner core with necrotic material and neutrophils (magnification 160×). (d) shows a low-power view of a liver of an infected mouse revealing extensive areas of caseous necrosis and a mantle of mycobacteria under the capsule (magnification 5×).