7 Glycocalyx composition and function in immune cell recruitment

What is the glycocalyx?

A carbohydrate rich pericellular matrix surrounding cell membranes

Where is the glycocalyx found?

On virtually all cells including endothelial immune epithelial and bacterial cells

Why is the glycocalyx considered evolutionarily ancient?

It appeared early in evolution including in marine single celled organisms

What is the thickness range of the endothelial glycocalyx?

Approximately 200 nm to 3 microns depending on context

What is the primary role of the endothelial glycocalyx in immune cell recruitment?

To act as a barrier inhibiting interaction between leukocytes and endothelium

Why does the glycocalyx pose a problem for leukocyte recruitment?

It protrudes further than endothelial adhesion molecules

Where are most immune cells produced?

In the bone marrow

Which immune cells are considered long lived?

Macrophages

Why is immune cell recruitment beneficial?

It allows immune cells to reach sites of infection

Why is immune cell recruitment harmful when uncontrolled?

It drives chronic inflammation such as rheumatoid arthritis

What are the main steps of leukocyte recruitment?

Rolling, chemokine signalling, integrin activation, firm adhesion, and extravasation

What happens during extravasation?

Leukocytes cross the endothelium usually between endothelial cells

What imaging techniques demonstrate the presence of the glycocalyx?

Electron microscopy, intravital imaging, and lectin staining

What happens to the glycocalyx after enzymatic digestion of glycans?

It becomes thinner and more disrupted

What do lectins bind to in glycocalyx imaging?

Specific glycan structures

How does glycocalyx structure differ between arteries and veins in the brain?

Arteries show distinct lectin peaks while veins often do not

What does heterogeneity of the glycocalyx mean?

Its structure varies by vessel type tissue and physiological state

What is a major component of the endothelial glycocalyx?

Proteoglycans

Which glycosaminoglycan is especially important in the endothelial glycocalyx?

Heparan sulfate

What role does hyaluronan play in the glycocalyx?

It contributes to structure and hydration

How is the glycocalyx remodeled during inflammation?

By enzymatic shedding and structural reorganisation

Which enzyme cleaves heparan sulfate?

Heparanase

What enzymes degrade proteoglycan core proteins?

Metalloproteinases

Which inflammatory cytokine is key in glycocalyx remodeling?

TNF

What is meant by patchy glycocalyx remodeling?

Localised thinning that allows immune cell interaction

Why must glycocalyx remodeling be local rather than systemic?

To restrict immune recruitment to specific sites

What experimental tool is used to mimic inflammation in vivo?

fMLP

What happens to lectin coated beads after fMLP injection?

Their interaction with vasculature decreases

What does decreased lectin bead binding indicate?

Shedding of glycocalyx glycans

What happens to leukocyte adhesion when the glycocalyx is degraded?

Leukocyte adhesion increases

How does pertussis toxin affect fMLP induced effects?

It reverses them by blocking GPCR signalling

What happens when heparan sulfate is enzymatically removed?

Adhesion molecule accessibility increases

Why is the glycocalyx not purely anti migratory?

Some glycans are required for immune cell recruitment

What other functions does the endothelial glycocalyx have?

Regulating vascular permeability and protecting from shear stress

How does the glycocalyx relate to the Starling principle?

It contributes to vascular filtration control

What role does the glycocalyx play in mechanosignalling?

It senses shear stress and triggers endothelial responses

What happens to the glycocalyx during sepsis?

It becomes degraded and thinned

What experimental molecule is used to model sepsis?

LPS

What effect does LPS have on glycocalyx thickness?

It causes a reduction in thickness

What happens in mice lacking TNF signalling after LPS exposure?

Glycocalyx thickness is preserved

What does this demonstrate?

TNF signalling is required for glycocalyx degradation

How does glycocalyx degradation affect neutrophil adhesion?

It increases adhesion to endothelium

What drug can reduce glycocalyx degradation effects?

Heparin

Why does heparin reduce leukocyte adhesion?

It inhibits enzymes involved in glycocalyx shedding

What happens in heparanase deficient mice during inflammation?

Leukocyte adhesion is reduced

Which diseases are associated with glycocalyx damage?

Sepsis, ARDS, viral infections, and COVID

Why are serum glycocalyx components measured in disease?

To indicate glycocalyx shedding

What cell types also possess a glycocalyx?

Immune cells themselves

Which immune cells show high heparan sulfate expression?

Neutrophils and monocytes

What happens to immune cell glycocalyx during inflammation?

It is shed or remodeled

How was immune cell glycocalyx studied experimentally?

Using flow cytometry

What did psoriasis models reveal about glycocalyx shedding?

Heparan sulfate was shed from immune cells not endothelium

Why might immune cells remodel their own glycocalyx?

To facilitate adhesion and migration

What happens when immune cell heparan sulfate is enzymatically removed?

Their adhesion to endothelium increases

Why must leukocyte recruitment consider two glycocalyces?

Both endothelial and immune cell glycocalyces regulate interaction

Where else is the glycocalyx critically important?

Epithelial surfaces kidney glomerulus and tumours

What role does the glycocalyx play in cancer?

It protects tumour cells and limits immune infiltration

How might glycocalyx structure affect metastasis?

By regulating tumour cell extravasation

What is the overall conclusion of the lecture?

The glycocalyx is a dynamic regulator of immune cell recruitment and disease