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
P Selectins are associated with which of the following processes in leukocytes? 
Select and explain. 
A. Rolling, B. Adhesion, C. Margination, D. All of the above
A: Rolling
Answer: A: Rolling 
Explanation: The initial rolling interactions are mediated by a family of proteins called selectins. There are three types of selectins: one expressed on leukocytes (L-selectin), one on endothelium (E-selectin), and one in platelets and on endothelium (P-selectin). Ref: Robbins, 8th edition, Chapter 2.