Final answer:
Hyperacute transplant rejection is caused by host antibodies that activate the complement system, leading to the destruction of the transplanted organ. In type II hypersensitivity reactions, such as hemolytic transfusion reactions, the binding of antibodies to the mismatched cells also activates the complement cascade, resulting in cell destruction.
Step-by-step explanation:
Hyperacute transplant rejection is caused by host antibodies against the donor organ, which activate the complement system. The complement system is a group of proteins that play a role in the immune response. When activated, it can cause cell damage and inflammation.
In the case of hyperacute transplant rejection, the host antibodies recognize the donor organ as foreign and bind to it. This binding triggers the complement system, leading to the destruction of the transplanted organ through the activation of immune cells and inflammatory responses.
For example, in a type II hypersensitivity reaction, such as a hemolytic transfusion reaction, if a person with type B blood receives a transfusion of type A blood, the recipient's anti-A antibodies will bind to and agglutinate the transfused red blood cells (RBCs). This binding also activates the complement cascade, leading to the destruction of the mismatched RBCs.