Alloantigenii

Alloantigens are antigens that are found in some members of a species but not in others. They are therefore capable of inducing an immune response in an individual who is genetically different from the individual who possesses the alloantigen. The most well-known examples of alloantigens are those found on the surface of red blood cells, which are responsible for the ABO and Rh blood group systems. Mismatched blood transfusions can lead to a severe immune reaction due to these alloantigens, as the recipient's immune system recognizes the foreign antigens and attacks the transfused red blood cells.

Beyond red blood cells, alloantigens are also present on other cell types and tissues. For instance, human leukocyte antigens (HLAs) are highly polymorphic alloantigens found on the surface of most nucleated cells in the body. These HLAs play a crucial role in the immune system's ability to distinguish between self and non-self. When an organ transplant occurs, the recipient's immune system identifies the donor's HLAs as foreign, leading to graft rejection. Immunosuppressive drugs are often administered to dampen this immune response and prevent the recipient's body from rejecting the transplanted organ. The study of alloantigens is fundamental to understanding blood transfusion compatibility, organ transplantation success, and certain autoimmune diseases.