- Host Hyperacute Rejection of donor organs occurs within minutes to hours following transplantation. This mechanism of transplant rejection requires the presence of pre-formed anti-donor antibody within the host.
- Hyperacute Rejection only occurs if the host possesses pre-formed anti-donor antibody. In such a scenario, pre-formed anti-donor antibodies rapidly bind antigens on donor tissue and result in activation of complement or directly recruit host macrophages and neutrophils via their Fc Region. More seriously, widespread activation of the coagulation cascade results in occlusive thrombosis of donor organ vasculature. Pre-formed antibodies must be the result of prior exposure to donor antigens which may occur in those who have previously received transfusions of blood possessing donor antigens or in women who have carried multiple pregnancies where the fetus possessed paternal antigens similar to that of the donor.
- Hyperacute Rejection usually becomes apparent within minutes after vascular anastomosis between host and donor organ. The donor organ rapidly loses color and becomes flaccid due to reduced perfusion from widespread occlusive thrombosis. Because stringent antigenic matching is performed between host and donor, hyperacute rejection occurs rarely today.