ABOrelated

ABOrelated describes topics connected to the ABO blood group system, named after its discovery by Karl Landsteiner. The ABO system classifies human blood based on the presence or absence of A and B antigens on the surface of red blood cells and the corresponding antibodies in plasma. The four major phenotypes are A, B, AB, and O. The A and B antigens are produced by glycosyltransferase enzymes encoded by the ABO gene on chromosome 9. The H antigen is a common precursor; a functional A or B transferase converts H to A or B antigen, while an inactive allele yields type O.

Immunologically, most people have natural anti-A or anti-B antibodies, primarily IgM, which react with non-self A or B antigens. This system underpins transfusion and transplantation medicine; compatibility requires matching ABO type to avoid acute hemolytic reactions. In pregnancy, ABO incompatibility can cause mild neonatal jaundice, and rarely more severe disease, but it is generally less severe than Rh incompatibility.

ABO-related topics also include the expression of ABO antigens beyond red blood cells. Secretor status (FUT2 gene) determines whether soluble A or B antigens appear in body fluids and mucosal tissues, which can influence susceptibility to certain pathogens, and has implications for serology and transplantation.

Population genetics study ABO frequency variation among populations and explore associations with disease risk or infection susceptibility; however, many proposed links are observational and context-dependent. The term ABO-related also appears in forensic, paternity, and research contexts where ABO typing remains a practical tool.