WBR0276

Author	[[PageAuthor::Ogheneochuko Ajari, MB.BS, MS [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pathology
Sub Category	SubCategory::Pulmonology, SubCategory::General Principles
Prompt	[[Prompt::A 34- year old man presents to the physician’s office with a 3-month history of cough, night sweats and weight loss. Past medical history is unremarkable. Physical examination, chest X ray and Sputum AFB confirms Mycobacterium tuberculosis. Which one of the following would be a step in the sequence of formation of a tuberculous granuloma in this patient?]]
Answer A	AnswerA::The tubercle bacillus undergoes necrosis by alveolar macrophages
Answer A Explanation	AnswerAExp::Incorrect. The tubercle bacillus undergoes phagocytosis and not necrosis by alveolar macrophages
Answer B	AnswerB::The tubercle bacillus undergoes phagocytosis by alveolar macrophages
Answer B Explanation	AnswerBExp::Correct- See explanation
Answer C	AnswerC::Macrophages release IL-4 and IL 2
Answer C Explanation	AnswerCExp::Incorrect. IL-12 and not IL 4 stimulate the formation of the TH1 cells and then IL 1 and not IL 2 activates the TH1 cells and causes fever
Answer D	AnswerD::Enzymes from killed tubercle bacillus lead to caseous necrosis
Answer D Explanation	AnswerDExp::Incorrect. Lipids and 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::Incorrect. Activated macrophages fuse, not neutrophils 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 and systemic fungal infections or non-infectious such as Sarcoidosis and Crohn’s disease. The sequence of steps includes: The tubercle bacillus Mycobacterium tuberculosis undergoes phagocytosis by alveolar macrophages (processing of bacterial antigen) Macrophages present 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 factor Lipids from killed tubercle bacillus lead to caseous necrosis Activated macrophages fuse and become multinucleated giant cells Reference: Goljan Rapid Review 2nd edition Pg 32 Educational Objective: References: ]]
Approved	Approved::Yes
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