FIG. 3.

Detail of the acellular rim delineating the calcified center of the primary granuloma. (A) High magnification of a primary lesion from lungs of an M. tuberculosis-infected guinea pig treated for 6 weeks with the combination therapy INH-RIF-PZA. The residual primary lung lesion is evidenced by central necrosis with incomplete dystrophic calcification (indicated by an “N”). Calcified necrotic debris is the granular basophilic material that forms a well-delineated margin from an acellular, rim (arrows) that blends with the fibrous capsule that contains predominantly lymphocytes and fewer macrophages. The lesion is well delineated from the normal lung parenchyma by a fibrous capsule. Magnification, ×200 (H&E stain). (B) Another high-magnification image of a primary lung lesion from an INH-RIF-PZA treated guinea pig infected with M. tuberculosis. The lesion shows extensive calcification and still has an acellular, rim (arrow) that blends with the fibrous capsule that contains predominantly lymphocytes and fewer macrophages. More normal lung parenchyma is seen at the section margins. Magnification, ×200 (H&E stain).