Early in apoptosis, viable neighboring cells and macrophages recognize dying cells before they lyse because of a change on the outer leaflet of the plasma membrane. What is this change?

• A Deposition of C3b on the membrane
• B Loss of CD47 expression
• C Exposure of mannose residues
• D Externalization of phosphatidylserine ✓

Explanation

In healthy cells the membrane phospholipid phosphatidylserine is confined to the inner leaflet by flippase activity. Early in apoptosis, scramblase activation allows phosphatidylserine to flip to the outer leaflet, where it acts as an eat-me signal promoting phagocytosis by macrophages and adjacent cells, explaining why apoptosis proceeds without inflammation. Mannose exposure marks senescent erythrocytes for splenic clearance, and C3b deposition is an opsonization event of complement, not an apoptosis-specific signal.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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