Acute GVHD is caused by?

Ans. is 'b' i.e., T lymphocyteGraft versus host (gvh) diseasesGraft versus host disease occurs in any situation in which immunologically competent cells or their precursors are transplanted into immunologically crippled patients and the transferred cells recognize alloantigens in the host.Graft versus host disease occurs most commonly in the setting of allogenic bone marrow transplantation but may also follow transplantation of solid organs rich in lymphoid cells (e.g. the liver) or transfusion of unirradiated blood.Recipients of bone marrow transplants are immunodeficient because of either their primary disease or prior treatment of the disease with drugs or irradiation.When such recipients receive normal bone marrow cells from allogenic donors, the immunocompetent, T cells present in the donor marrow recognizes the recipient's HLA antigen as foreign antigen and react against them. Both CD4+ and CD8+T cells recognize and attack host tissues.In clinical practice GVH can be so severe that bone marrow transplants are done only between HLA matched donor and recipient.