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. 2018 Feb 6;7(1):19. doi: 10.3390/pathogens7010019

Figure 2.

Figure 2

Bronchial obstruction and intracellular accumulation of MTB antigens in developing post-primary TB. The tree-in-bud sign on high resolution CT scan (A) is characteristic of developing post-primary TB. It is formed by obstructed bronchioles (tree) and alveoli filled with foamy macrophages (buds). Bronchial obstruction (arrow in B) is found in 100% of cases of TB (H&E, 40 magnification). Immunohistochemistry (IHC) stain with rabbit polyclonal antibody against whole killed MTB (C,D) shows MTB antigens to be intracellular in alveolar macrophages in viable lung tissue. MTB are seldom found in such lesions by either IHC or AFB staining suggesting that very few MTB secrete antigens that are stored for a prolonged period in these cells prior to induction of caseous pneumonia. (C 700×, D 100× magnification).