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File:IPLab6TB6.jpg|This is a high-power (oil immersion) photomicrograph of granuloma stained with an acid-fast stain. Mycobacterium tuberculosis bacilli stain red.
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== Study Questions ==
* <spoiler text="What is the Ghon complex?">In primary pulmonary TB you get (1) parenchymal subpleural lesions, often just above or just below the interlobar fissure, and (2) enlarged caseous lymph nodes draining the parenchymal focus (usually the hilar lymph nodes).</spoiler>
* <spoiler text="What factors are responsible for the virulence of M. tuberculosis?">M. tuberculosis has no known exotoxins, endotoxins or histolytic factors. Its pathogenicity is due to the fact that it resists phagocytic killing and sets up a delayed hypersensitivity reaction. Virulent M. tuberculosis organisms have cord factor, sulfatides, LAM, heat shock protein and they activate complement.</spoiler>
* <spoiler text="What is the sequence of events after primary exposure to M. tuberculosis?">The initial infection with M. tuberculosis leads to a T cell-mediated immune response that controls 95% of infections. Alveolar macrophages phagocytose the organisms and then transport them to the hilar lymph nodes. Macrophages cannot kill the mycobacteria so the organisms multiply, lyse the host cell, infect other macrophages, and sometimes disseminate via the blood to other parts of the lung and elsewhere in the body.
After a few weeks, T cell-mediated immunity develops and leads to activation of macrophages so they can kill intracellular mycobacteria via reactive nitrogen intermediates. This process leads to formation of epithelioid cell granulomas and clearance of the mycobacteria. Also, CD8+ suppresser T cells kill macrophages that are infected with mycobacteria, resulting in the formation of caseating granulomas. These processes during the primary infection with M. tuberculosis result in a calcified scar in the lung parenchyma and in the hilar lymph node. This combination is called the Ghon complex.
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{{IPLab 6}}
[[Category: IPLab:Lab 6]]
