Caseating granulomas are the histological hallmark of tuberculosis. The central caseous necrosis in tuberculosis granulomas is a form of coagulative necrosis with a distinctive 'cheese-like' gross appearance. The caseous necrosis results from which unique mechanism?
- A Bacterial lipopolysaccharide directly activating complement cascade causing membrane attack complex-mediated lysis
- B Eosinophilic abscess formation with tissue digestion by eosinophil major basic protein
- C Liquefactive necrosis secondary to neutrophil degranulation around the bacillus
- D CD4+ Th1-mediated delayed hypersensitivity reaction causing macrophage death through perforin/granzyme and TNF, combined with lipid-rich mycobacterial cell wall components ✓
Explanation
Caseous necrosis in tuberculosis results from the interaction of Th1-mediated delayed-type hypersensitivity (DTH) with the unique lipid-rich cell wall of M. tuberculosis. Sensitised CD4+ Th1 cells release IFN-γ, activating macrophages, and secrete TNF, which together cause macrophage necrosis; the abundant complex lipids (mycolic acids, cord factor) in the bacillary cell wall and surrounding tissues impede normal proteolytic digestion, creating the characteristic opaque, cheese-like consistency. This combination of tissue necrosis with incomplete digestion due to lipid accumulation is unique to mycobacterial granulomas.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.