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
Most important antigen initiating graft rejection 
Select and explain. 
A. MHC - molecule, B. Polysaccharide, C. DHA, D. HLA - Antigen
D: HLA - Antigen
Answer: D: HLA - Antigen 
Explanation: the most important consequence of direct recognition is the activation of CD8+ T cells 
which recognise class I MHC molecules in the graft.Host CD4+ helper T cell may be triggered into proliferation and cytokine production by recognition of donor
class II MHC molecules  and drive an inflammatory response