Selectins

Definition

Selectins are a family of cell adhesion molecules that play a crucial role in the process of cell-cell interactions, particularly in the immune response and inflammation. They are expressed on the surface of endothelial cells and leukocytes, mediating the initial steps of leukocyte rolling along blood vessel walls and subsequent adhesion to tissues during inflammatory responses.

5 Must Know Facts For Your Next Test

1. Selectins exist in three main types: E-selectin (expressed on endothelial cells), P-selectin (found on activated platelets and endothelial cells), and L-selectin (expressed on leukocytes).
2. Selectins bind to specific carbohydrate ligands on the surface of leukocytes, initiating rolling interactions that are critical for leukocyte recruitment during inflammation.
3. The engagement of selectins with their ligands leads to conformational changes that enhance the adhesive properties of integrins, allowing for stronger binding and extravasation of leukocytes into tissues.
4. Selectin-mediated rolling is a rapid and transient process, allowing leukocytes to efficiently survey the vascular endothelium for sites of injury or infection.
5. Dysregulation or abnormal expression of selectins can contribute to various diseases, including chronic inflammatory conditions and autoimmune disorders.

Review Questions

• How do selectins contribute to the process of leukocyte rolling and adhesion during inflammation?
  • Selectins mediate leukocyte rolling along the endothelium by binding to specific carbohydrate ligands on leukocytes. This interaction causes a slow rolling motion as leukocytes make transient contacts with the blood vessel walls. As this rolling continues, integrins on the leukocyte surface become activated, leading to firm adhesion and eventual transmigration into tissues where they can mount an immune response.
• Discuss the differences between E-selectin, P-selectin, and L-selectin in terms of their expression patterns and functional roles.
  • E-selectin is primarily expressed on activated endothelial cells in response to pro-inflammatory cytokines, while P-selectin is found on activated platelets and endothelial cells. L-selectin is expressed on circulating leukocytes. Each selectin plays a unique role: E-selectin is crucial for recruiting neutrophils during acute inflammation, P-selectin mediates platelet-leukocyte interactions, and L-selectin facilitates homing of lymphocytes to peripheral lymph nodes.
• Evaluate the implications of selectin dysregulation in disease processes such as chronic inflammation and autoimmune disorders.
  • Dysregulation of selectins can lead to either excessive or insufficient recruitment of leukocytes to sites of inflammation. In chronic inflammatory conditions, overexpression of selectins may result in sustained leukocyte infiltration, perpetuating tissue damage and pathology. Conversely, inadequate selectin function may impair immune responses in autoimmune disorders, where timely recruitment of immune cells is critical. Understanding these mechanisms could pave the way for targeted therapies that modulate selectin activity in various diseases.

Related terms

Integrins: Integrins are another class of cell adhesion molecules that facilitate cell-extracellular matrix interactions and are involved in signaling pathways that regulate cell behavior.

Leukocyte: Leukocytes, or white blood cells, are key components of the immune system, responsible for defending the body against infections and foreign substances.

Endothelial Cells: Endothelial cells line the interior surface of blood vessels and play a vital role in vascular biology, including regulating blood flow and maintaining barrier function.