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': 'All are affected in Graft-Versus host reaction except: \nSelect and explain. \nA. Skin, B. Lung, C. G.I.T, D. Liver', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Graft versus host disease\n\nGraft versus host disease occurs in any situation in which immunologically competent cells or their precursors\xa0are transplanted into immunologically crippled patients and the transferred cells recognize alloantigen’s in the\xa0host.\nGraft versus host disease occurs most commonly in the setting of allogeneic bone marrow transplantation but\xa0may also follow transplantation of solid organs rich in lymphoid cells (e.g. the liver) or transfusion of\xa0uneradicated blood.\nRecipients of bone marrow transplants are immunodeficient because of either their primary disease or prior\xa0treatment of the disease with drugs or irradiation.\nWhen such recipients receive normal bone marrow cells from allogeneic donors, the immunocompetent, T cells\xa0present in the donor marrow recognize the recipient’s HLA antigen as a foreign antigen and react against them.\xa0Both 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 HIA matched\xa0donor and recipient\nAcute GVH disease occurs within days to weeks after allogeneic bone marrow transplantation.\nAlthough any organ may be affected\xa0the major clinical manifestation results from involvement of the immune\xa0system and epithelia of the skin, liver and intestines.\nInvolvement of the skin in GVH disease is manifested by a generalized rash leading to desquamation in severe\xa0cases.\nDestruction of small bile ducts gives rise to jaundice and mucosal ulceration of the gut results in bloody\xa0diarrhoea.\nImmunodeficiency\xa0is a frequent accompaniment of GVH disease the immunodeficiency\xa0may be a result of prior\xa0treatment, myeloablative preparation for the graft, a delay in repopulation of the recipient’s immune system and\xa0attack on host’s immune cells by grafted lymphocytes.\nAffected individuals are profoundly immunosuppressed and are easy prey to infections. Although many different\xa0types of organisms may infect patients, infection with cytomegalovirus is particularly important.', 'role': 'assistant'}]