Blood-Group Substance
Definition
Soluble ABO antigens (A substance, B substance, H substance) present in the body fluids of secretors. Chemically distinct from the glycolipid-bound cell-surface antigens but carrying the same specificities.
- Chemical form
- Soluble ABO antigens (A, B, H substance)
- Found in
- Body fluids of ABO secretors (saliva, semen, sweat)
- Contrast with
- Cell-surface antigens, which are glycolipid-bound
- Forensic role
- Historic basis for ABO typing of non-blood body fluid stains
Common questions
Why can blood-group substance be typed from saliva or semen but not from a non-secretor's fluids?+
Only individuals with a functional secretor gene produce soluble ABO antigens that diffuse into body fluids beyond blood. In non-secretors, the ABO antigens remain confined to the glycolipid-bound cell-surface form on red cells, so their saliva or semen carries no typeable soluble substance.
Is blood-group substance testing still used in casework given modern DNA methods?+
It has been largely superseded by STR and other DNA profiling, which give far greater individualising power. ABO secretor typing survives mainly as historical case reference material or in resource-limited settings, and it is not treated as primary identification evidence in modern forensic practice.
Related terms
- FUT2 Gene
- The Fucosyltransferase 2 gene on chromosome 19q13, encoding the alpha-1,2-fucosyltransferase enzyme responsible for adding fucose to type-1 chain precursors in secretory tissues...
- Inhibition Index
- A quantitative measure of PCR inhibitor burden in a DNA extract, derived from the Ct shift of an internal positive control (IPC)...
- Non-Secretor
- An individual homozygous for non-functional FUT2 alleles who produces no H, A, or B antigen in saliva, semen, or other exocrine secretions,...
- Se Gene / Se428
- The original notation for the secretor locus (Se for secretor, se or FUT2*428A for the non-secretor null allele carrying a nonsense mutation...
- Secretor
- An individual whose ABO blood group antigens are expressed on red blood cells and also released into body fluids such as saliva,...