Cytotoxic T lymphocytes kill virus-infected target cells by expressing Fas ligand, which engages Fas (CD95) on the target cell membrane. Which event immediately follows this ligand-receptor interaction in the target cell?
- A Formation of a death-inducing signaling complex with adaptor proteins and activation of caspase-8 ✓
- B Translocation of cytochrome c from mitochondria to the cytosol
- C Oligomerization of BAX and BAK in the mitochondrial outer membrane
- D Phosphorylation of MLKL leading to membrane rupture
Correct answer: A. Formation of a death-inducing signaling complex with adaptor proteins and activation of caspase-8
Explanation
The extrinsic pathway of apoptosis is initiated when Fas ligand binds Fas, recruiting the adaptor protein FADD to form the death-inducing signaling complex. This activates initiator caspase-8, which cleaves executioner caspases-3 and -7 directly. Cytochrome c release and BAX/BAK oligomerization belong to the intrinsic mitochondrial pathway, triggered by growth factor withdrawal or DNA damage, not by death receptors. MLKL phosphorylation defines necroptosis.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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