A 63-year-old woman comes to the emergency department with fever and a cough. A new medical student rotating in the emergency department is sent to interview and examine the patient. The patient reports 3 months of fevers, night sweats, and a productive cough, and is subsequently placed in an isolation room. A chest x-ray demonstrates a right apical lung lesion. The medical student has never been exposed to Mycobacterium tuberculosis and reports that he was in close contact with the patient, who coughed frequently during their interaction. Which of the following would most likely happen during the first week after exposure?

Question

A 63-year-old woman comes to the emergency department with fever and a cough.  A new medical student rotating in the emergency department is sent to interview and examine the patient.  The patient reports 3 months of fevers, night sweats, and a productive cough, and is subsequently placed in an isolation room.  A chest x-ray demonstrates a right apical lung lesion.  The medical student has never been exposed to Mycobacterium tuberculosis and reports that he was in close contact with the patient, who coughed frequently during their interaction.  Which of the following would most likely happen during the first week after exposure?

Quizplus · Accepted Answer

11ec160b_38a4_3747_9249_736ecb81be6c_MD0001_00 Mycobacterium tuberculosis is a facultative intracellular, acid-fast bacillus that is transmitted via aerosolized droplet nuclei. The pathogen is inhaled into the lower lobe of the lung and replicates within the alveoli. Alveolar macrophages phagocytose the organism but are initially unable to eliminate it due to microbial virulence factors (eg, cord factor) that prevent phagolysosome fusion and acidification. This allows M tuberculosis to replicate in an unchecked fashion within the phagosome of alveolar macrophages for the first few weeks of the infection. After a few weeks, antigen-presenting cells in the draining lymphatic system display mycobacterial antigens and release interleukin-12, which stimulates naïve CD4 lymphocytes to differentiate into T helper type 1 (T_H1) cells. T_h1 cells release interferon-gamma (Choice B), which activates macrophages and causes them to: Form fully acidified phagolysosomes that are capable of destroying intracellular mycobacteria Differentiate into epithelioid cells and multinucleated Langhans giant cells that surround extracellular mycobacteria within granulomas (Choice A). These cells release digestive enzymes and generate reactive oxygen species, which helps limit mycobacterial proliferation but also cause caseating necrosis and (in some patients) cavitary lung lesions (Choice E). (Choice D) Although B lymphocytes form antibodies against M tuberculosis, antibodies play a minimal role in the elimination of facultative intracellular organisms (intracellular bacteria are shielded from immunoglobulins). Educational objective: Primary tuberculosis infection is marked by initial unchecked Mycobacterium tuberculosis replication within the alveolar space and alveolar macrophages. After a few weeks, CD4 lymphocytes are stimulated to release interferon-gamma, which activates macrophages and leads to control of the infection. __________ References: The tuberculous granuloma: an unsuccessful host defence mechanism providing a safety shelter for the bacteria? (http://www.ncbi.nlm.nih.gov/pubmed/22811737) Immunology of tuberculosis. (http://www.ncbi.nlm.nih.gov/pubmed/24804000)

A 63-Year-Old Woman Comes to the Emergency Department with Fever