In type AB blood, A antigens and B antigens are present on the red blood cells, according to the National Center for Biotechnology Information. The serum portion of AB blood does not contain any blood antibodies.
There are four blood types found in humans: A, B, AB and O. Blood type depends on which antigens are present on the red blood cells and the antibodies in the blood serum, explains the National Center for Biotechnology Information. Blood serum contains antibodies for the antigens that are not present on the red blood cells, so type A blood has red blood cells with A antigens and serum containing anti-B antibodies, while type B blood has red blood cells with B antigens and serum with anti-A antibodies. Blood type AB red cells have both A and B antigens with no blood antibodies in the serum, and O blood has neither A nor B antigens on the red blood cells but contains both anti-A and anti-B serum antibodies.