5th February 2024

Adhesion molecules

The interaction between a cell and its surroundings ( i.e. the extracellular matrix (ECM)) is heavily dependent on molecular interactions between the cell surface and extracellular molecules. This can be seen as either cell-cell interactions or cell-ECM component interactions.

These molecules are essential for basic physiological functions, including cell migration, cell growth, immunological processes, cell repair, embryogenesis and cell differentiation.

The important adhesion molecules covered in this topic include cadherins, immunoglobulin superfamily, selectins and integrins.

Cadherins

The cadherin superfamily consists of several molecules, including the desmogleins, desmocollins and cadherins. These molecules are dependent on calcium ions to enable their adhesive functions.

These molecules are essential in the embryological development of vertebrates by allowing accurate cell migration by differential expression of specific cadherin molecules. Cadherins are also crucial in maintaining normal cell structure and movement.

Immunoglobulin superfamily

This refers to a large family of cell surface proteins that contain an immunoglobulin domain. These molecules can mediate cell-cell adhesion without calcium ions.

These molecules are typically involved with cellular processes such as antigen presentation, white blood cell surface receptors and axonal development. Other Ig superfamily molecules act as integrin ligands ( e.g. ICAM).

Integrins

These are a group of transmembrane receptors that are heterodimers. These aid in the cell’s interaction with the ECM. These receptors typically bind to proteins in the ECM, including laminin, fibronectin and fibrinogen. However, some subsets will bind to immunoglobulins.

Some functions mediated by integrins include cell cycle regulation, apoptosis stimulation, cell cytoskeleton organisation, and cellular response to changes in the ECM. For example, the binding of WCC to antigens and platelet response to damaged blood vessels are mediated by integrins.

Certain genetic conditions like leukocyte adhesion deficiency are caused by deficiency of integrin subunits. In this condition, this prevents usual leukocyte expression of the β2 subunit, preventing extravasation of the leukocytes to sites of infection.

Selectin

Selectins are predominantly found on leukocytes, platelets and endothelial cells. These are expressed as part of the inflammatory response. This allows leukocytes to migrate to the site of inflammation and extravasate from blood vessels.