Hyperacute graft rejection is caused by Select one: A. type IV hypersensitivity. B. hyperactivated helper T cells. C. proliferation of smooth muscle cells. D. arteriosclerosis. E. pre-existing host antibodies.
The correct answer and explanation is:
The correct answer is E. pre-existing host antibodies.
Hyperacute graft rejection is an immediate and severe form of rejection that occurs within minutes to hours after transplantation. It is primarily caused by pre-existing host antibodies that react with antigens on the graft’s endothelial cells. These antibodies are usually specific to blood group antigens or human leukocyte antigens (HLA) that are present on the graft but not on the host’s own tissues.
The immune response in hyperacute rejection occurs rapidly. When the donor organ is transplanted, the pre-existing antibodies in the recipient’s bloodstream bind to the endothelial cells of the graft. This leads to the activation of the complement system and the formation of immune complexes, which in turn causes widespread endothelial damage. The endothelial cells become injured and undergo necrosis, resulting in thrombosis (clot formation) and occlusion of blood vessels in the transplanted organ. This can rapidly lead to the failure of the graft.
The reason for the presence of pre-existing antibodies can be due to a previous organ transplant, blood transfusion, or pregnancy, where the recipient may have been sensitized to foreign HLA or blood group antigens. In such cases, the body’s immune system has already developed antibodies against these antigens, which are then recognized as foreign when the organ is transplanted.
Hyperacute rejection is different from other forms of rejection, such as acute or chronic rejection, which are mediated by T cells. Hyperacute rejection is not associated with the activation of T cells or the proliferation of smooth muscle cells, and it does not involve arteriosclerosis, which is a condition that develops over time in chronic rejection. Therefore, pre-existing antibodies are the key factor in this immediate, life-threatening rejection process.