Question

Explain how a white blood cell (leukocyte) uses protein-sugar interactions within a blood vessel to find the site of inflammation. Specify which proteins are involved in binding to which types of sugars during this process, and on which surface each of these ligands & receptors would be found

Answer 1

White blood cells or leucocytes are recruited to the site of inflammation by a series of overlapping steps known as the leukocyte adhesion cascade. It is initiated by the recognition of certain pathogen associated molecular patterns (PAMPs) and involves a number of sugar-protein interactions. The two major adhesion receptor families involved in this process are selectins and integrins. These adhesion molecules help in the rapid attachment of the leucocytes to the walls of the blood vessels.

Selectins include:

P-selectins which are expressed on the endothelial cells and platelets. They bind PSGL-1 as ligand.

E-selectins which are expressed on the endothelend cells after the P-selectins. They bind PSGL-1 and ESL-1 as ligands.

L-selectins which are expressed ob certain leucocytes constitutively. They bind to glyCAM-1, madCAM-1 and CD34 as ligands.

The integrins include:

LFA-1 which is present on the circulating leucocytes and binds with ICAM-1 and ICAM-2 on the endothelial cells.

Mac-1 which is present on the circulating leucocytes and binds with ICAM-1.

VLA-4 which is present on the leucocytes and endothelial cells and has a major role in chemotaxis. It binds to the vascular cell adhesion protein-1 or VCAM-1.