Alloantigeenid

Alloantigeenid are antigens that differ between individuals of the same species and can provoke an immune response in a recipient exposed to them. They arise from genetic polymorphisms that cause variable expression of surface proteins, such as human leukocyte antigen (HLA) and other blood group determinants. Exposure occurs most notably through transplantation, transfusion, or pregnancy.

Major alloantigeenid include HLA antigens (MHC class I and II) and ABO blood group antigens. Minor histocompatibility antigens are other polymorphic peptides that can elicit responses, particularly in the context of allogeneic bone marrow transplantation. These alloantigeenid may be recognized by T cells and, in some cases, by antibodies, leading to alloimmune reactions.

In transplantation, mismatched alloantigeenid are a primary cause of graft rejection. Donor-derived alloantigeenid presented by recipient antigen-presenting cells stimulate T cells and can drive B-cell production of alloantibodies. Hyperacute rejection can occur with ABO incompatibility, while acute and chronic rejections are driven by HLA and minor antigen mismatches. In hematopoietic stem cell transplantation, donor T cells reacting to host alloantigeenid can cause graft-versus-host disease.

Sensitization to alloantigeenid can result from prior transfusions, pregnancies, or transplants, leading to preformed alloantibodies. Compatibility testing includes HLA typing and crossmatching to detect these antibodies, along with ensuring ABO compatibility. Detection methods often involve serology and advanced typing techniques such as flow cytometry or molecular haplotyping.

Understanding alloantigeenid is essential for transplantation planning, transfusion safety, and pregnancy management in sensitized individuals. Strategies to mitigate responses include careful donor–recipient matching, immunosuppressive therapy, and desensitization procedures when appropriate.