A 35-year-old HIV-positive man with a CD4 count of 70 cells/μL presents with fever, night sweats, and bilateral upper lobe infiltrates with cavitation on chest X-ray. Sputum culture grows acid-fast bacilli. The predominant mechanism of tissue destruction in pulmonary tuberculosis is:

• A Direct cytotoxicity by mycobacterial exotoxins
• B Antibody-dependent complement-mediated lysis
• C Type IV delayed-type hypersensitivity mediated by sensitized CD4+ T cells ✓
• D Neutrophil extracellular trap formation

Explanation

Tuberculosis tissue injury is primarily immunopathological, driven by CD4+ Th1 T-cell–mediated delayed-type hypersensitivity (Type IV reaction). Macrophages activated by IFN-γ from sensitized T cells form granulomas, and central caseation necrosis results from the local cytokine milieu combined with tissue ischemia. In immunocompromised patients like those with HIV, the T-cell response is blunted, leading to atypical presentations with less cavitation and more dissemination.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.