This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Rejection of Transplants, Subject name: Pathology
Antigen involved in post transplant rejection? 
Select and explain. 
A. HL A-Antigen, B. Nuclear antigen, C. Polysaccharide, D. DHA
A: HL A-Antigen
Answer: A: HL A-Antigen 
Explanation: Ans. is 'a' i.e., HLA - antigen o For rejection of graft, there must be some antigen that is recognized as foreign and the most important antigen is HLA antigen of grafted tissue.