antigensystem

An antigen system is an organized set of related antigens that share structural, genetic, or functional relationships and are used to classify immune-recognized markers on cells, pathogens, or molecules. The term is often applied in immunology and transfusion medicine to describe families of surface molecules that elicit antibody responses and are important in compatibility testing, disease susceptibility, and immune recognition.

Common examples include blood group antigen systems, such as ABO and Rh, which are defined by specific carbohydrate or protein determinants on red blood cells and have direct relevance to transfusion safety and hemolytic disease of the newborn. The human leukocyte antigen (HLA) system is another major antigen system; its highly polymorphic proteins present peptides to T cells and are central to organ transplantation compatibility and autoimmune disease associations. Pathogen antigen systems group related surface or secreted proteins that influence immunity, vaccine design, and antigenic variation.

Antigen systems are characterized genetically by loci that encode the antigenic molecules; polymorphisms at these loci create different antigenic variants (alleles). Detection methods include serological assays that use antibodies to identify antigens and molecular typing techniques that analyze underlying genes. Clinically, antigen systems guide transfusion matching, donor selection, and transplant planning, and they inform epidemiology and immunogenetics research. Their study integrates structural biology, genetics, and clinical immunology.