FIG. 5.

Lungs and mesenteric lymph nodes from guinea pigs showing the hypoxic regions in the primary granulomas 4 months after M. tuberculosis infection. (A) Residual primary lung lesion near a major airway with central necrosis surrounded by epithelioid macrophages that are stained by immunohistochemistry for pimonidazole adducts. The center of the lesion, likely hypoxic, fails to stain due to the lack of viable cells. Magnification, ×40 (hematoxylin counterstain). (B) Residual primary lung lesion with dystrophic calcification and secondary lesion resulting from hematogenous dissemination and inflammation Magnification, ×40 (H&E stain), both indicated by arrows. (C) Primary lung lesion with central necrosis surrounded by epithelioid macrophages that are stained by immunohistochemistry for pimonidazole adducts. Magnification, ×100 (hematoxylin counterstain). (D) Mediastinal lymph node where the normal architecture is replaced by mixed inflammation composed primarily of macrophages and with an extensive, central focus of lytic necrosis. Magnification, ×40 (H&E stain). (E) Mediastinal lymph node with the area of central necrosis surrounded by epithelioid macrophages that are stained by immunohistochemistry for pimonidazole adducts. The center of the lesion, likely hypoxic, fails to stain due to the lack of viable cells (necrosis). Magnification, ×40 (hematoxylin counterstain).