This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunity, Subject name: Pathology
Allograft rejection is an example of? 
Select and explain. 
A. GVHD, B. Delayed types hypersensitivity, C. Immediate hypersensitivity, D. Acute rejection
B: Delayed types hypersensitivity
Answer: B: Delayed types hypersensitivity 
Explanation: Ans. (b) Delayed type hypersensitivity(Ref: Robbins 9th/pg 231-234; 8th/pg 221-229; Refer Ans 200)Types of Rejection Pathway:Direct pathway: CD4 and CD8-T cells of the transplant recipient recognize allogeneic (donor) MHC molecules on the surface of APCs in the graft.Indirect pathway: recipient CD4-T lymphocytes recognize MHC antigens of the graft donor after they are presented by the recipient's own APCs.As both the pathways are cell mediated, hence they are delayed hypersensitivity reactions.