During the course of a routine physical examination two months prior to admission, this 57-year-old white male was noted to have a lesion in the upper lobe of the right lung. Initially, he was treated for two weeks with ampicillin. He was then admitted to an outside hospital for further study. All studies including sputum studies for tubercle bacilli, bronchial washings, and bronchoscopy were negative and he was discharged. Review of systems revealed the presence of mild dyspnea on exertion, accompanied by a slightly productive cough. Of interest was the fact that the patient had been PPD positive for the past 4 to 5 years, but this had never been evaluated. On this hospital admission, physical and laboratory examinations were negative. Radiographic examination of the chest revealed a 2 x 2-cm density in the right lower lung field. Several small cavities were identified in this area on CT scan.

== Images ==

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 ==

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]]