This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Misc. (W.B.C), Subject name: Pathology
Leukocyte common antigen is: 
Select and explain. 
A. CD 45, B. CD 20, C. CD 19, D. CD 41
A: CD 45
Answer: A: CD 45 
Explanation: Ans. (a) CD 45(Ref: Robbins 9th/pg 590; 8th/pg 600; Wintrobe's 12th/pg 2522)CD 45Found in all hematopoietic cells except erythrocytes.CD45 plays an essential role in lymphocyte activation.Peripheral blood naive T cells are CD45RA, whereas memory (activated) T cells are CD45RO+