During the early phases of acute inflammation, leukocytes roll along the vascular endothelium before becoming firmly adherent. Which molecular pair mediates this initial rolling step?

• A Integrins (LFA-1, Mac-1) binding to ICAM-1 on endothelium
• B PECAM-1 (CD31) homotypic interactions at intercellular junctions
• C Selectins (E-selectin, P-selectin) on endothelium binding sialyl-Lewis X-modified ligands on leukocytes ✓
• D VLA-4 integrin binding to VCAM-1 on endothelium

Explanation

Rolling is mediated by selectins: E-selectin and P-selectin induced on activated endothelium bind sialyl-Lewis X-modified glycoproteins on leukocytes, creating weak, easily broken bonds. Integrin binding to ICAM-1 mediates the subsequent firm adhesion step, which is the tempting distractor. VCAM-1 with VLA-4 mainly supports lymphocyte and monocyte adhesion, and PECAM-1 mediates transmigration through endothelial junctions, not rolling.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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