Which antibodies are found in the blood serum of people with type A blood?

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Close-up illustration of multiple human red blood cells with their characteristic disc shape, floating against a red background. — blood group The major component of human blood is the red blood cell.

People with type A blood have red blood cells that express A antigens on their surface. Consequently, their blood serum contains anti-B antibodies, which are designed to identify and combine with type B antigens.123

These naturally occurring antibodies are present in the plasma even without prior exposure to type B red cells. If a person with type A blood receives a blood transfusion containing type B red cells, these anti-B antibodies will attack the foreign cells, leading to a transfusion reaction.312