Alloimmune

Alloimmune

The term "alloimmune" refers to the immune response that occurs when the immune system of one individual reacts against antigens from another individual of the same species. This response is a critical concept in the fields of transplantation, blood transfusion, and pregnancy.

Overview

Alloimmunity, also known as isoimmunity, involves the immune system recognizing and responding to non-self antigens from the same species. This can lead to various clinical conditions, depending on the context in which the alloimmune response occurs.

Mechanisms

The alloimmune response is primarily mediated by the recognition of foreign antigens by T cells and B cells. These antigens are typically proteins or glycoproteins expressed on the surface of cells. The most common alloantigens include:

• Human Leukocyte Antigens (HLA): These are major histocompatibility complex (MHC) molecules that play a crucial role in the immune system's ability to distinguish self from non-self.
• ABO blood group antigens: These are carbohydrate antigens present on the surface of red blood cells.

Clinical Implications

Transplantation

In the context of organ or tissue transplantation, alloimmune responses can lead to graft rejection. This occurs when the recipient's immune system attacks the transplanted organ or tissue, recognizing it as foreign. There are different types of rejection, including:

• Hyperacute rejection: Occurs within minutes to hours after transplantation, often due to pre-existing antibodies against donor antigens.
• Acute rejection: Occurs days to weeks after transplantation, mediated by T cells.
• Chronic rejection: Develops over months to years, involving both cellular and humoral immune responses.

Blood Transfusion

Alloimmune reactions can also occur during blood transfusions if the donor and recipient blood types are not compatible. This can lead to hemolytic transfusion reactions, where the recipient's immune system destroys the transfused red blood cells.

Pregnancy

During pregnancy, alloimmune responses can occur when the mother is exposed to fetal antigens. This can lead to conditions such as hemolytic disease of the newborn (HDN), where maternal antibodies attack fetal red blood cells.

Management

Managing alloimmune responses involves:

• Immunosuppression: Medications such as cyclosporine, tacrolimus, and corticosteroids are used to suppress the immune response in transplant recipients.
• Blood typing and crossmatching: Ensuring compatibility between donor and recipient blood types to prevent transfusion reactions.
• Rh immunoglobulin: Administered to Rh-negative mothers to prevent HDN.

Research and Future Directions

Research in alloimmunity focuses on improving transplant outcomes, developing better immunosuppressive therapies, and understanding the mechanisms of alloimmune diseases. Advances in genomics and immunology continue to provide insights into alloimmune responses and potential therapeutic targets.

Also see

• Autoimmune disease
• Immunology
• Transplant rejection
• Blood transfusion
• Pregnancy complications