Activated cytotoxic T lymphocytes kill virus-infected target cells by engaging Fas on the target cell surface. Immediately downstream of Fas ligand binding, the adaptor protein FADD recruits and activates which initiator caspase?

• A Caspase-9
• B Caspase-3
• C Caspase-12
• D Caspase-8 ✓

Explanation

Trimerization of Fas by Fas ligand recruits FADD through death domain interactions, forming the death inducing signaling complex (DISC). FADD binds procaspase-8 via death effector domains, bringing multiple caspase-8 molecules together for autocatalytic activation. Active caspase-8 then directly cleaves executioner caspase-3, and also cleaves BID to engage the mitochondrial amplification loop. Caspase-9 is the initiator of the intrinsic apoptosome pathway.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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