Cytotoxic T lymphocytes kill virus-infected target cells by delivering preformed proteins through perforin pores. Which molecule delivered by CTLs directly cleaves and activates caspase-3 inside the target cell?

• A Granzyme B ✓
• B Fas ligand
• C Tumor necrosis factor alpha
• D Bim

Explanation

CTLs secrete perforin, which polymerizes into pores in the target cell membrane, and granzyme A, a serine protease that enters through these pores. Granzyme A can directly cleave and activate caspase-3 and can also trigger the mitochondrial pathway via Bid. Fas ligand and TNF-alpha act through surface death receptors rather than perforin pores, representing the second, contact-independent mechanism of CTL killing. Bim is a BH3-only pro-apoptotic protein, not a CTL product.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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