Alloantigen

Alloantigen

An alloantigen is an antigen that is present in some but not all individuals of the same species. These antigens are recognized as foreign by the immune system of individuals who do not possess them, leading to an immune response. Alloantigens are important in the context of blood transfusion, organ transplantation, and pregnancy.

Structure and Function

Alloantigens are typically proteins or glycoproteins found on the surface of cells. They are encoded by polymorphic genes, meaning that there are multiple alleles of these genes within a population. This genetic diversity results in the presence or absence of specific alloantigens in different individuals.

The most well-known alloantigens are the human leukocyte antigens (HLA) in humans, which are part of the major histocompatibility complex (MHC). These molecules play a crucial role in the immune system by presenting peptides to T cells.

Clinical Significance

Blood Transfusion

In the context of blood transfusion, alloantigens are responsible for blood group differences. The ABO blood group system and the Rh blood group system are the most clinically significant alloantigen systems. Mismatched blood transfusions can lead to hemolytic transfusion reactions, where the recipient's immune system attacks the transfused blood cells.

Organ Transplantation

Alloantigens are critical in organ transplantation, where the donor and recipient must be matched for HLA antigens to reduce the risk of graft rejection. The immune system of the recipient can recognize the donor's alloantigens as foreign, leading to an immune response against the transplanted organ.

Pregnancy

During pregnancy, the fetus expresses paternal alloantigens that are foreign to the mother. The maternal immune system can produce antibodies against these alloantigens, which can lead to conditions such as hemolytic disease of the newborn if the antibodies cross the placenta and attack fetal red blood cells.

Research and Applications

Research into alloantigens has led to advances in immunology and transplant medicine. Understanding the genetic basis of alloantigen diversity helps in developing better matching techniques for blood transfusions and organ transplants. Additionally, studying alloantigens can provide insights into autoimmune diseases and immune tolerance.

Also see

• Antigen
• Immunology
• Transplant rejection
• Blood group system
• Major histocompatibility complex