A cytology smear from a resolving viral infection shows cells with condensed nuclear chromatin and intact plasma membranes. Which surface change allows macrophages to recognize and phagocytose these apoptotic cells without triggering inflammation?

• A Expression of CD95 (Fas) ligand on the cell surface
• B Loss of membrane cholesterol with increased fluidity
• C Exposure of phosphatidylserine on the outer leaflet of the plasma membrane ✓
• D Release of high mobility group box 1 protein bound to the membrane

Explanation

During apoptosis, the enzyme scramblase flips phosphatidylserine from the inner to the outer leaflet of the plasma membrane. Externalized phosphatidylserine is the eat-me signal recognized by macrophage receptors, permitting quiet phagocytosis without inflammation. HMGB1 is released by necrotic cells and acts as a DAMP that promotes inflammation, which is exactly what apoptosis avoids. Fas is a death receptor on the dying cell, not a recognition signal for phagocytes.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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