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
[{'content': 'True about GVHD is? \nSelect and explain. \nA. Occurs when host is immunocompetent, B. Most common organ involved is lung, C. Most common in renal transplant, D. Occurs when donor cells are immunocompetent', 'role': 'user'}, {'content': "Answer: D \nExplanation: Graft versus host (GVH) Disease:\n\nGraft versus host disease occurs in any situation in which immunologically competent cells or their\xa0precursors are transplanted into immunologically crippled patients and the transferred cells recognize\xa0alloantigens in the host.\nGraft versus host disease occurs most commonly in the setting of allogeneic bone marrow transplantation\xa0but may also follow transplantation of solid organs rich in lymphoid cells (e.g. the liver) or transfusion of\xa0un-irradiated blood.\nRecipients of bone marrow transplants are immunodeficient because of either their primary disease or prior treatment of the disease with drugs or irradiation.\nWhen such recipients receive normal bone marrow cells from allogeneic donors, the immunocompetent, T\xa0cells present in the donor marrow recognizes the recipient's HLA antigen as foreign antigen and react\xa0against them. Both CD4+ and CD8+T cells recognize and attack host tissues\nIn clinical practice, GVH can be so severe that bone marrow transplants are done only between HLA\xa0matched donor and recipient\nThere are three principal target tissues affected in GVHD : Skin, liver, and gut", 'role': 'assistant'}]