P-selectin

Platelet selectin also known as (CD62P, GMP-140 and PADGEM) plays an important role. It is manufactured and stored in intracellular granules in vascular endothelial cells (in Weibel-Palade bodies) and in platelets in $\alpha$ granules. It's molecular weight is 140 Kd.

The main ligand for P-selectin is the carbohydrate derivative termed sialyated Lewis.

Stimulation of the endothelium by hypoxia, free radicals, peroxides, histamine and thrombin results in expression of P-selectin on the surface of the endothelial cells, see figure 4. Maximum levels of P-selectin are reached on the surface of the endothelial cell within 3-10 minutes and without further stimulation levels fall back to normal within 30 minutes to 3 hours depending on the stimulus for expression, thrombin/histamine fast and oxidants prolonged. Expression of P-selectin makes the venular endothelium sticky to leucocytes. This may result in rolling even in the absence of L-selectin.

Leucocyte rolling may be obliterated by the use of antibodies against P-selectin and in P-selectin ``knockout'' mice.

In the absence of P-selectin, L-selectin may induce rolling but in this case the rolling is much faster indication that L-selectin is less efficient at inducing rolling than P-selectin. However L-selectin is required for the normal inflammatory response.