Selectins are vascular adhesion molecules that mediate physiological responses such as inflammation, immunity and hemostasis. The selectins are a family of three C-type lectins expressed by bone-marrow-derived cells and endothelial cells. These vascular cell adhesion molecules are identified as L-selectin expressed on leukocytes, E-selectin expressed on endothelial cells ad P-selectin expressed on platelet and endothelial cells. All three selectins have a similar structure consisting of an amino-terminal lectin domain, one EGF-like domain, several consensus repeats, a single transmembrane domains and a carboxy-terminal cytoplasmic domain. The main physiological function of all selectins is to mediate leukocyte recruitment to sites of inflammation or to lymphoid tissues. 
P-selectin is found in secretory granules of platelets (α-granules) and endothelial cells (Weibel-Palade bodies) and upon activation is present on the surface of platelets and endothelial cells. E-selectin expression on activated endothelial cells requires de novo transcription, thus occurs several hours after stimulation and persists for a longer time period as observed in chronic inflammation. L-selectin is expressed by all myeloid-derived cells, naïve T cells, and some memory T cells. Selectins promote tumor cell-endothelial interaction and the recruitment of leukocytes. a: Platelet binding to tumor cells and to the endothelium promote tumor cell adhesion. The intracellular signaling in leukocytes is initiated through selectin-binding to PSGL-1 on leukocytes resulting in 1: activation of MAPK and src kinase pathways; 2: activation of integrins; 3: activation of NF-κB pathways and secretion of cytokines (e.g. CCL2, IL-8 or TNF-α; 4: shedding of cell surface L-selectin.

References

1.Lubor Borsig. Glycobiology. 2018 Aug 31; 28(9): 648–655.