alloantigének

Alloantigének (alloantigens) are antigens that originate from another individual of the same species and are recognized as foreign by the immune system of a different individual. They arise from genetic polymorphism in tissue- and cell-surface molecules, most notably the human leukocyte antigen (HLA) system, as well as other polymorphic surface antigens such as ABO and Rh blood group antigens. Because of this variation, exposure to alloantigens through transfusion, transplantation, or pregnancy can elicit an alloimmune response.

The immune response involves both T and B cells. T cells can react via direct presentation of donor HLA peptides by donor cells or indirect presentation by recipient antigen-presenting cells. B cells can form alloantibodies against donor HLA and other alloantigens, leading to antibody-mediated rejection.

Clinical relevance: In organ or stem cell transplantation, donor and recipient ideally are matched for HLA alleles and ABO compatibility; crossmatching and panel reactive antibody testing assess risk of rejection. Even with HLA matching, minor histocompatibility antigens can trigger rejection or graft-versus-host disease if donor T cells recognize recipient alloantigens, especially in allogeneic bone marrow transplantation.

In transfusion medicine, alloantigen incompatibilities in ABO, Rh, and other blood group systems can cause hemolytic transfusion reactions. Alloantigen exposure during pregnancy can cause maternal alloimmunization, potentially affecting the fetus or newborn.

Detectability: HLA typing, serology, PCR-based methods, and crossmatch testing are used to identify incompatibilities.