Sialyl-Lewis X is linked to  __________.
Selectin
ICAM
CD31
VCAM
The two major families of molecules involved in leukocyte adhesion and migration are the selectins and integrins  
These  molecules  are  expressed  on leukocytes and endothelial cells.
Selectins mediate the initial weak interactions between leukocytes  and  endothelium.