Pathophysiology of GVHD. Injury to host epithelia and endothelium generates injury signals that recruit donor T cells. In this inflammatory milieu, the donor T cells recognize minor histocompatibility antigens, resulting in activation and proliferation. The T cells then cause further injury through both specific and nonspecific mechanisms. This process is amplified by endotoxin. The clinical manifestations of this process are seen in GVHD. PMN, polymorphonuclear leukocyte; NK, natural killer.