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
Antigen involved in post transplant rejection - 
Select and explain. 
A. HLA - Antigen, B. Nuclear antigen, C. Polysaccharide, D. DHA
A: HLA - Antigen
Answer: A: HLA - Antigen 
Explanation: Ans. is 'a' i.e., HLA - antigen For rejection of graft, there must be some antigen that is recognized as foreign and the most impoant antigen is HLA antigen of grafted tissue.