Question

What does diapedesis refer to?

• A. Attachment of neutrophils to blood vessel
• B. Escape of neutrophils from capillaries through the capillary endothelium
• C. Stimulation of cytokine secretion by inflammatory cells
• D. Response of mediator cells to cytokine secretion

Hint:

Diapedesis is the physical step where neutrophils cross the capillary endothelium into tissue, after adhesion.

Answer 1

The Correct Option is B

Diapedesis is one specific step in how a neutrophil gets from the blood into inflamed tissue, so each option needs to be checked against where it sits in that journey.

1. Attachment of neutrophils to blood vessel: This describes adhesion, an earlier step where integrins on the neutrophil bind ICAM-1 on the endothelium. It happens before diapedesis, not during it.
2. Escape of neutrophils from capillaries through the capillary endothelium: This is exactly diapedesis, the neutrophil squeezing between endothelial cells and moving out of the vessel into the tissue.
3. Stimulation of cytokine secretion by inflammatory cells: This is chemical signalling that helps recruit and activate cells, not the physical crossing of the vessel wall.
4. Response of mediator cells to cytokine secretion: Again a signalling event, describing how cells react to chemical messengers, not a physical movement across the endothelium.

Only the second option describes the actual physical event of a neutrophil leaving the capillary lumen and entering the tissue, which is the definition of diapedesis.

Let's summarize:

• Diapedesis follows adhesion in the leukocyte extravasation sequence.
• It is the physical transmigration of the neutrophil across the endothelium, not a signalling event.

The correct answer is escape of neutrophils from the capillary across the endothelium.