This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General anatomy, Subject name: Anatomy
Cell surface molecules involved in peripheral tolerance 
Select and explain. 
A. B7 and CD28, B. CD40 and CD40L, C. CD 34 and CD51, D. B7 and CD3
A: B7 and CD28
Answer: A: B7 and CD28 
Explanation: Ref Robbins 7/e p225 , Harrison 16/e p1907, Robbins 9/e p213 B7 is a type of peripheral membrane protein found on activated antigen presenting cells that, when paired with either a CD28 or CD152 surface protein on a T cell, can produce a costimulatory signal