This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
Sialyl-Lewis X is linked to  __________. 
Select and explain. 
A. Selectin, B. ICAM, C. CD31, D. VCAM
A: Selectin
Answer: A: Selectin 
Explanation: 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.