Review Question - QID 106654

Integrin molecules are involved in the adhesion of leukocytes to endothelial cells.

Neutrophil accumulation in the area of an infection or injury is important in the immune system's defense against infection. Extravasation is the process by which neutrophils exit blood vessels across the vessel wall to enter tissues. Extravasation relies on the interplay between neutrophils and endothelial cells, which have been activated by cytokines released during local tissue damage.

Reust discusses leukocyte adhesion deficiency (LAD) in children. LAD is a disorder affecting phagocytic cells. Several molecular defects in integrin molecules or in the ligands for endothelial selectins can cause LAD. The disorder usually presents within the first few weeks after birth. Delayed separation of the umbilical cord (> 4 weeks) is a classic finding, as are recurrent bacterial infections and the absence of pus formation.

Newton et al. discuss the process of extravasation. Tissue damage results in the release of cytokines, which activate the endothelium, thereby increasing the expression of selectins. Selectins on the endothelium loosely interact with neutrophils to initiate margination and rolling. Subsequent interaction between integrins (such as LFA-1) on neutrophils with ICAM-1 on endothelial cells mediates adhesion. Subsequently, neutrophils transmigrate between endothelial cells.

Illustration A is a schematic of the steps involved in neutrophil extravasation. Illustration B is a histologic image showing transmigration of neutrophils across the endothelial surface of a blood vessel.

Incorrect answers:
Answer 1: ICAM is involved in adhesion.
Answer 2: LFA-1 is involved in adhesion, not margination.
Answers 4,5: E-selectin is involved in margination and rolling.