WBR0276

Author	[[PageAuthor::Ogheneochuko Ajari, MB.BS, MS [1] (Reviewed by Alison Leibowitz)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pathology
Sub Category	SubCategory::Pulmonology, SubCategory::General Principles
Prompt	[[Prompt::A 34-year-old male presents to the physician’s office with a 3-month history of cough, night sweats, and weight loss. Physical examination, a chest X ray, and Sputum AFB confirm Mycobacterium tuberculosis. Which of the following would be a step in the formation of a tuberculous granuloma in this patient?]]
Answer A	AnswerA::The tubercle bacillus undergoes necrosis by alveolar macrophages
Answer A Explanation	AnswerAExp::The tubercle bacillus undergoes phagocytosis, but not necrosis, by alveolar macrophages
Answer B	AnswerB::The tubercle bacillus undergoes phagocytosis by alveolar macrophages
Answer B Explanation	AnswerBExp::See explanation
Answer C	AnswerC::Macrophages release IL-4 and IL-2
Answer C Explanation	AnswerCExp::IL-12, not IL-4, stimulates the formation of the TH1 cells and then IL-1, not IL-2, activates the TH1 cells and leads to fever.
Answer D	AnswerD::Enzymes from killed tubercle bacillus lead to caseous necrosis
Answer D Explanation	AnswerDExp::Lipids, not enzymes, from the killed bacillus lead to caseous necrosis.
Answer E	AnswerE::Activated neutrophils fuse to become multinucleated giant cells
Answer E Explanation	AnswerEExp::Activated macrophages, not neutrophils, fuse to become multinucleated giant cells.
Right Answer	RightAnswer::B
Explanation	[[Explanation::Tuberculous granuloma formation is a specialized form of chronic inflammation which is either caused by infections such as Tuberculosis or systemic fungal infections or by non-infectious causes such as Sarcoidosis or Crohn’s disease. The sequence of tuberculous granuloma formation: Tubercle bacillus Mycobacterium tuberculosis undergoes phagocytosis by alveolar macrophages (processing of bacterial antigen). Macrophages present the antigen to CD4 T cells in association with class II antigen sites. Macrophages release IL-12 which stimulates the formation of TH1 class cells and IL-1, which causes fever, and activates TH1 cells. TH1 cells release IL-2, gamma interferon, and migration inhibitory factors. Lipids from killed tubercle bacillus result in caseous necrosis. Activated macrophages fuse and become multinucleated giant cells. Educational Objective: Tuberculous granuloma formation is a specialized form of chronic inflammation which is either caused by infections such as Tuberculosis or systemic fungal infections or by non-infectious causes such as Sarcoidosis or Crohn’s disease. References: Goljan Rapid Review 2nd edition Pg 32]]
Approved	Approved::Yes
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