Selectins

Selectins are cell surface glycoproteins that bind carbohydrate ligands and participate in transient cell-cell adhesion.

All selectins comprise an N-terminal lectin domain and an epidermal growth factor or EGF domain that regulate binding specificity and strength.

However, the number of sequence-conserved-repeats or SCR domains can vary from two to nine repeats depending on the type of selectin.

The short L-selectins expressed on immune cells like lymphocytes help them migrate into lymph nodes by binding ligands on the endothelial cells.

The larger P-selectins are primarily expressed on platelets. They aid in aggregating platelets and immune cells at the site of injury.

A third type, called E-selectins, is temporally expressed along with P-selectins on endothelial cells during an immune response.

These selectins form weak, transient interactions with free-flowing leukocytes and slow them down.

The leukocytes then roll along the endothelial surface, where other cell adhesion molecules help recruit them to the appropriate tissue microenvironments — a process called leukocyte homing.