The ABO Blood Group

The ABO blood group system is based on the presence of specific antigens or agglutinogens on the red blood cells, or RBCs, and antibodies or agglutinins in the blood plasma.

The RBC membranes have two genetically determined glycolipid antigens, A and B.

Those individuals with either A or B antigens are assigned blood groups A or B, respectively.

Individuals who carry both A and B antigens are assigned blood group AB.

In contrast, individuals who lack both antigens form the O blood group.

The blood plasma contains antibody molecules, which cannot cause agglutination or clumping while interacting with self-RBC antigens.

So, an individual with blood group A has anti-B antibodies in their plasma. In contrast, anti-A antibodies are present in the plasma of an individual with blood group B.

Since the AB blood group has both A and B antigens, these individuals lack both anti-A and anti-B antibodies in the plasma.

Lastly, individuals in the O blood group have both antibodies in their plasma.