Question

Leukocyte migration through endothelium is induced by -

• A. Selectin
• B. N CAM
• C. C CAM
• D. PECAM

Hint:

Transmigration (diapedesis) is mediated by PECAM-1 (CD31).

Answer 1

The Correct Option is D

Step 1: Name the step. Migration of leukocytes across the endothelial wall into tissue is called transmigration or diapedesis, and it occurs mainly in postcapillary venules.

Step 2: Identify the molecule. The key adhesion molecule that mediates transmigration is CD31, also called PECAM-1 (platelet endothelial cell adhesion molecule-1). It belongs to the immunoglobulin superfamily and is present on both leukocytes and endothelial cell junctions, allowing the leukocyte to squeeze between cells. So option d, PECAM, is correct.

Step 3: Place it in the cascade. The full leukocyte recruitment cascade is rolling (selectins), firm adhesion (integrins binding ICAM/VCAM), and finally transmigration (PECAM-1). PECAM acts at the last, transmigration step.

Step 4: Why the others are wrong. Selectins mediate the earlier rolling phase, not transmigration. N-CAM is a neural cell adhesion molecule and C-CAM is not the transmigration mediator. Therefore PECAM is the answer.