H Antigen
Definition
A fucose-containing oligosaccharide on red cell surfaces and secreted epithelial cells, produced by FUT1 (on red cells) and FUT2 (in secretions). It is the precursor substrate for ABO transferase enzymes. All ABO-active antigens are built on H antigen.
- Chemical nature
- Fucose-containing oligosaccharide
- Produced by
- FUT1 gene on red cells, FUT2 in secretions
- Role
- Precursor substrate for ABO transferase enzymes
- Field
- Forensic serology and blood group genetics
Common questions
What happens to a person who lacks functional H antigen?+
This rare condition, the Bombay phenotype, leaves no substrate for ABO transferases to act on, so the person types as O on routine ABO testing even if they carry A or B alleles genetically, and they can only safely receive blood from other Bombay-phenotype donors.
How does H antigen connect blood typing to genetic ABO testing?+
Because H antigen is the shared starting material, differences in the final ABO phenotype come entirely from which transferase enzyme, if any, a person's ABO alleles produce. This links the serological blood test directly to the underlying ABO genotype used in forensic and paternity casework.
Related terms
- ABO Transferase
- A glycosyltransferase enzyme encoded by the ABO gene on chromosome 9. The A allele encodes an enzyme that adds N-acetylgalactosamine to H...
- Agglutination
- Clumping of red cells that occurs when antibodies in serum bind to incompatible antigens on the cell surface, cross-linking cells into visible...
- Antigen
- A molecule recognised by the adaptive immune system through specific binding to an antibody or T-cell receptor. Defined by immunogenicity (capacity to...
- Bombay Phenotype (Oh)
- A rare phenotype in which individuals lack functional H antigen on red cells and in secretions due to mutations in FUT1 (and...
- Forensic Serology
- The branch of forensic science concerned with detecting and characterising biological fluids (blood, semen, saliva, vaginal secretions) as evidence in legal proceedings,...
- Forward Grouping (Cell Grouping)
- The direct test of red blood cells with known anti-A and anti-B reagent antibodies to determine which ABO antigens are present on...
- Glycosyltransferase
- The enzyme encoded by the ABO gene locus that attaches terminal sugar residues to the H antigen chain. Group A transferase adds...
- Isohemagglutinins
- The naturally occurring antibodies (anti-A and/or anti-B) present in serum from birth without prior transfusion or immunisation. Group A individuals carry anti-B;...
- Reverse Grouping (Serum Grouping)
- Testing a person's serum against known A1 and B reagent red cells to identify which antibodies are present. A healthy adult with...
- Secretor Status
- A genetic trait that determines whether a person expresses their ABO blood group antigens in secreted body fluids such as saliva, semen,...
Explained in these topics
- The ABO Blood Group System: Genetics and Serology
- ABO System: Biology and Forensic HistoryThe core fucosylated precursor oligosaccharide from which A and B antigens are biochemically constructed by glycosyltransferase enzymes. Group O individuals re...