Alloreaktivität

Alloreactivity refers to the immune response directed against foreign antigens present on cells from a genetically different individual of the same species. This phenomenon is most prominently observed in the context of organ transplantation and blood transfusions. When donor tissue or blood is introduced into a recipient, the recipient's immune system recognizes the donor's cells as foreign due to differences in their major histocompatibility complex (MHC) molecules, also known as human leukocyte antigens (HLA) in humans.

These MHC molecules are highly polymorphic, meaning they have many different variations within a population. The immune system, particularly T lymphocytes, is exquisitely sensitive to these differences. Upon encountering foreign MHC molecules, T cells become activated, leading to an immune response that can result in the rejection of the transplanted organ or the destruction of transfused blood cells.

The intensity of alloreactivity can vary. Factors such as the degree of MHC mismatch between donor and recipient, the type of immune cell involved, and the presence of pre-existing antibodies can influence the outcome. Understanding alloreactivity is crucial for the success of transplantation. Strategies like tissue typing to match MHC alleles and the use of immunosuppressive drugs aim to mitigate these immune responses and prevent graft rejection. While primarily known for its detrimental effects in transplantation, alloreactivity also plays a role in certain immune conditions and experimental immunology.