Cytotoxic T lymphocytes kill virus-infected target cells through engagement of a surface receptor that triggers the extrinsic pathway of apoptosis. Immediately after receptor trimerization, which sequence of molecular events follows?

• A FADD recruitment, caspase-8 activation, direct cleavage of executioner caspases ✓
• B Cytochrome c release, Apaf-1 binding, caspase-9 activation
• C RIPK1 autophosphorylation, MLKL phosphorylation, membrane rupture
• D BAX and BAK oligomerization, mitochondrial outer membrane permeabilization

Explanation

The extrinsic pathway begins when Fas ligand (or TNF) trimerizes its receptor, recruiting the adaptor protein FADD through death domains. FADD activates procaspase-8 within the death-inducing signaling complex (DISC), and caspase-8 directly cleaves and activates the executioner caspases without any mitochondrial involvement. Option B describes the intrinsic pathway, option C describes necroptosis, and option D describes mitochondrial permeabilization downstream of BH3-only proteins.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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