Rejection is normally a result of humoral and cell-mediated reactions of the recipient to some kinds of antigens contained by the donor tissue. These antigens are known as major histocompatibility complex (MHC) molecules. This type of molecules is connected to a human leukocyte antigen (HLA) complex molecules in humans. "The recognition of these foreign MHC antigens initiates rejection, which occurs in two stages. During the first stage, known as sensitization, lymphocytes are alerted and respond to the foreign MHC molecules. Rapid proliferation occurs in this stage. In the second 'effector' stage, the graft is destroyed by several cellular and molecular mechanisms. Following pages represent breif explanations of these mechanisms"(Biomed, 2004, Par.1).
Hyperacute rejection emerges as a rule within the first 24 hours after operation. This reaction begins so rapidly that the tissue never becomes vascularized. It is characterized by skin rash, abnormal liver activity fever and large susceptibility to infections.Hyperacute rejection is affected by presence host antibodies that turn to antigens present in out blood,so usually hyperacute rejection can be avoided by screening for anti-graft antibodies.
Acute rejection normally starts within first two wee