Antithetical Antigens
Definition
Pairs of antigens where carrying one typically excludes the other on the same protein: C and c, E and e in the Rh system; M and N on glycophorin A; S and s on glycophorin B. A person can be homozygous (CC or cc) or heterozygous (Cc).
- Rh system pairs
- C and c, E and e
- MNS system pairs
- M and N on glycophorin A, S and s on glycophorin B
- Genotype options
- Homozygous (CC, cc) or heterozygous (Cc)
- Forensic relevance
- Adds discriminating power beyond ABO in blood typing
Common questions
Why can't a person carry both antigens of an antithetical pair strongly?+
The two antigens are alternate products of the same gene locus, so a person's genotype determines which one or which combination of both they express, and testing for both members of the pair narrows the possible genotype more than testing for either alone.
How does typing antithetical antigens help when ABO alone is inconclusive?+
Because Rh and MNS antigen combinations are inherited independently of ABO, adding results for pairs like C/c or M/N increases the number of distinguishable blood group profiles, which can help differentiate stains from different individuals who happen to share the same ABO group.
Related terms
- Antigen Degradation Rate
- The rate at which an antigen becomes undetectable on a dried stain, driven by protein denaturation, microbial protease activity, UV exposure, and...
- Discriminating Power
- The statistical ability of a typing system to distinguish one individual from another in a given population. Expressed as the probability that...
- Glycophorin
- A family of heavily sialylated red-cell glycoproteins. Glycophorin A carries M and N antigens; glycophorin B carries S and s antigens. Both...
- MNS System
- A blood group system comprising M and N antigens on glycophorin A (GYPA) and S and s antigens on glycophorin B (GYPB)....
- Rh System
- A blood group system defined by antigens on two proteins encoded by the RHD and RHCE genes on chromosome 1. The clinically...