alloimmune

Alloimmune refers to an immune response directed against antigens from another individual of the same species who is genetically different. It involves alloantigens, which are antigenic differences that vary between individuals and can prompt immunity when exposure occurs. Common alloantigens include ABO and Rh blood group antigens, as well as human leukocyte antigens (HLA) and other histocompatibility determinants. Alloimmunization occurs when a person is exposed to foreign antigens through events such as blood transfusion, pregnancy with a fetus carrying paternal antigens, or solid organ or stem cell transplantation. The immune response can involve antibodies produced by B cells and T cell–mediated responses against donor antigens.

In transfusion medicine, alloantibodies can bind donor red cells and cause acute or delayed hemolytic transfusion reactions. In pregnancy, maternal alloantibodies against fetal red cell antigens can cross the placenta and cause hemolytic disease of the fetus and newborn. In solid organ transplantation, alloimmune responses contribute to graft rejection; in allogeneic hematopoietic stem cell transplantation, donor T cells can attack recipient tissues, a complication known as graft-versus-host disease.

Diagnosis typically relies on serologic and cellular assays to detect anti-donor antibodies and to determine antigen compatibility, such as crossmatching and panel reactive antibody testing. Prevention and management center on antigen matching, minimization of alloimmunization risk, leukoreduction of blood products when appropriate, and immunosuppressive strategies to control rejection or GVHD.