DurgicalDurgical
EN
Open the app

Immunology · Cytokines and molecules

Adhesion molecules: selectins and integrins !

  • Molecule

Selectins and integrins are the brakes and anchors that let white blood cells stop on a vessel wall and leave the blood to reach an infection.

Updated 2026-11-01

What it is

To leave the blood, a leukocyte follows a cascade: selectins slow it into rolling, chemokines activate its integrins, and integrins bind endothelial ligands (ICAM-1, VCAM-1, MAdCAM-1) for firm arrest before it crawls and crosses the wall. Inflammatory cytokines such as TNF-α and IL-1 switch these endothelial molecules on. Inherited defects of the cascade cause leukocyte adhesion deficiencies, and blocking integrins is a treatment for multiple sclerosis and Crohn disease.

Step by step

  1. TNF-α and IL-1 activate the endothelium, which displays selectins.
  2. Selectins catch the leukocyte and make it roll along the wall.
  3. Chemokines on the endothelium switch the leukocyte's integrins to high affinity.
  4. Integrins bind ICAM-1 or VCAM-1 and the cell stops firmly.
  5. The leukocyte crawls and crosses the endothelium (diapedesis) towards the chemokine gradient.

Clinical notes

  • LAD I (autosomal recessive, ITGB2): umbilical stump separates at 3 weeks or later, omphalitis, severe gingivitis and periodontitis, skin infections without pus, slow wound healing.
  • LAD II: a fucose-transporter defect prevents selectin ligands from forming.
  • LAD III: kindlin-3 defect; integrins are present but do not activate, with LAD I-like infections plus bleeding.
  • Natalizumab blocks entry of leukocytes into brain and gut; JC virus antibody testing before and during treatment estimates the PML risk.

In the lab

  • Flow cytometry for CD18 (and CD11) on leukocytes confirms LAD I.
  • Very high neutrophil counts in blood, even without infection, are typical of LAD.

Test yourself

Think of the answer, then tap the question to see it.

Which molecules mediate the rolling step of leukocytes?

Selectins: P- and E-selectin on endothelium and L-selectin on leukocytes, binding mainly PSGL-1.

A baby has delayed umbilical cord separation, omphalitis and infections without pus. Which molecule is missing?

The β2 integrin subunit CD18 (ITGB2 gene): leukocyte adhesion deficiency type I.

Which serious infection is linked to natalizumab?

Progressive multifocal leukoencephalopathy caused by the JC virus.

Add to my cards (3)

← All of immunology

Educational content on the immune system; not a treatment or individual vaccination guide and no substitute for a health professional's advice. No doses are given.

Sources: Cell Adhesion Molecules and Their Roles and Regulation in the Immune and Tumor Microenvironment (Frontiers in Immunology, 2019); Leukocyte adhesion deficiency type 1 (MedlinePlus Genetics (U.S. National Library of Medicine), 2025); Natalizumab Injection: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2025).

Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake

Representative model, for educational purposes only.