[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Immunology](https://durgical.com/en/immunology/) › [Cytokines and molecules](https://durgical.com/en/immunology/#a-molecules) › Adhesion molecules: selectins and integrins

[Immunology](https://durgical.com/en/immunology/) · [Cytokines and molecules](https://durgical.com/en/immunology/#a-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

## Key points

- Rolling: P-selectin (minutes, from Weibel-Palade bodies) and E-selectin (hours) on endothelium; L-selectin on leukocytes; main ligand PSGL-1.
- Activation: chemokines switch integrins to high affinity (inside-out signalling).
- Firm arrest: LFA-1 (β2 integrin) binds ICAM-1; VLA-4 (α4β1) binds VCAM-1.
- LAD type I: β2 integrin (ITGB2, CD18) defect, delayed cord separation, infections without pus, leukocytosis.
- Natalizumab (anti-α4 integrin): multiple sclerosis and Crohn disease; risk of PML from JC virus.

## 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

- TNF-α and IL-1 activate the endothelium, which displays selectins.
- Selectins catch the leukocyte and make it roll along the wall.
- Chemokines on the endothelium switch the leukocyte's integrins to high affinity.
- Integrins bind ICAM-1 or VCAM-1 and the cell stops firmly.
- 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.

## Memory aid

Selectins are the brake, chemokines the switch, integrins the anchor: brake, switch, anchor, then out through the wall.

## 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.

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## Related

- [IL-8 and the chemokines](https://durgical.com/en/immunology/il-8-and-the-chemokines/)
- [TNF-α](https://durgical.com/en/immunology/tnf/)
- [Interleukin-1](https://durgical.com/en/immunology/interleukin-1/)
- [IL-4, IL-5 and IL-13 (the Th2 cytokines)](https://durgical.com/en/immunology/il-4-il-5-and-il-13/)
- [Neutrophil](https://durgical.com/en/immunology/neutrophil/)
- [Acute inflammation: vascular and cellular events](https://durgical.com/en/immunology/acute-inflammation-vascular-and-cellular-events/)
- [Phagocyte defects: CGD, LAD, Chédiak–Higashi](https://durgical.com/en/immunology/phagocyte-defects-cgd-lad-chediak-higashi/)

## Related conditions

- [Multiple sclerosis](https://durgical.com/en/conditions/multiple-sclerosis/)
- [Crohn disease](https://durgical.com/en/conditions/crohn-disease/)

[← All of immunology](https://durgical.com/en/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](https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2019.01078/full) (Frontiers in Immunology, 2019); [Leukocyte adhesion deficiency type 1](https://medlineplus.gov/genetics/condition/leukocyte-adhesion-deficiency-type-1/) (MedlinePlus Genetics (U.S. National Library of Medicine), 2025); [Natalizumab Injection: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a605006.html) (MedlinePlus (U.S. National Library of Medicine), 2025).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/immunology/adhesion-molecules-selectins-and-integrins/