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
[{'content': 'Sialyl-Lewis X is linked to  __________. \nSelect and explain. \nA. Selectin, B. ICAM, C. CD31, D. VCAM', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The two major families of molecules involved in leukocyte adhesion and migration are the selectins and integrins\xa0\xa0\nThese\xa0 molecules\xa0 are\xa0 expressed\xa0 on leukocytes and endothelial cells.\nSelectins mediate the initial weak interactions between leukocytes\xa0 and\xa0 endothelium.', 'role': 'assistant'}]