General characteristics of blood types
Medicine and biology are currently aware of over three hundred different antigen-antibody systems. However, only two of them have the greatest practical and clinical significance:
- The AB0 system.
- The Rhesus system.
The antigenic properties of blood are determined by the structural diversity of glycoproteins — specifically, oligosaccharides. Several classifications exist, but AB0 and the Rhesus factor remain fundamental, dividing people into Rhesus-positive and Rhesus-negative.
Etiology of incompatibility: AB0 and Rhesus systems
The main cause of immunological conflicts is incompatibility between mother and fetus regarding the Rhesus factor or the AB0 system. Other antigen systems are involved extremely rarely.
- Rhesus conflict: develops when the mother has Rhesus-negative blood (Rh-) and the developing fetus has Rhesus-positive blood (Rh+).
- AB0 incompatibility: occurs when the mother has blood type 0 (I), while the fetus is diagnosed with type A (II) — observed in 65% of cases, or type B (III) — in 35% of cases.
It is worth noting that AB0 incompatibility is registered more frequently than Rhesus conflict, but it mostly proceeds in a mild form, which is why it often remains undiagnosed.
Dual incompatibility and clinical guidelines
A special case is dual incompatibility. This is a clinical situation in which the mother has blood group O and Rh-negative — 0(I) Rh(-), while the fetus has inherited group A or B with Rh-positive — A(II) Rh(+) or B(III) Rh(+).
Under such circumstances, hemolytic disease of the newborn (HDN) manifests primarily through the AB0 system (due to antigens A or B), rather than the Rhesus factor.
According to clinical guidelines (Level of Evidence — 5, Level of Recommendation — C), determining the main blood types according to the AB0 system and detecting the D antigen of the Rhesus system is mandatory. The clinical rationale for this is preparation for a possible blood transfusion in the event of hemorrhage.
Antigens are oligosaccharides (O-oligo-saccharides). AB0 and Rhesus are the main pair for transfusion and conflicts.
Class and exam questions
How many antigen-antibody systems are currently known in total?
Currently, science knows of more than 300 antigen-antibody systems.
Which two systems have the greatest clinical significance?
The AB0 system and the Rhesus system are of substantial practical importance.
Why does AB0 incompatibility occur and how does it manifest?
It occurs if the mother has blood type 0(I) and the fetus has A(II) (in 65% of cases) or B(III) (in 35% of cases). It is more common than Rhesus conflict, but is predominantly mild in nature.
What determines the antigenic properties of blood at the molecular level?
Antigenic properties are determined by the structural diversity of oligosaccharides (glycoproteins).
What else to study on this topic
- Detailed analysis of over 300 antigen-antibody systems
- Mechanisms of development of hemolytic disease of the newborn in dual incompatibility
- Biochemical structure of blood oligosaccharides and glycoproteins
- Rules for performing blood transfusions taking into account the AB0 system
- Criteria for evaluating levels of recommendation (Level C) and levels of evidence (Level 5)
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