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NBME 21 Answers

nbme21/Block 3/Question#43

An undernourished 70-year-old man has fever, night ...


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submitted by nala_ula(38),

M. tuberculosis replicates in an unchecked fashion within the alveoli and alveolar macrophages due to virulence factors (cord factor) that prevent macrophage-mediated phagolysosome destruction. After a few weeks, macrophages infected display antigen on MHC II to stimulate T CD4+ cells which leads to an increase in interferon-y (Th1 cytokine) that active macrophages. Activated macrophages can also differentiate into epithelioid histiocytes and coalesce into multinucleated Langhans giant cells that wall off extracellular mycobacteria within granulomas.

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submitted by dr.xx(47),

In most individuals infected with M. tuberculosis, mononuclear cells in the blood release interferon-gamma when stimulated with antigens derived from M. tuberculosis.


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submitted by temmy(26),

how i remember it for all granulomas formed by...IFN gamma Maintained by TNF alpha

Gamma forms alpha maintains (sustains it). That is why infliximab and etarnacept( TNF alpha inhibitors) will break down the granuloma if used.