Video Transcript
Consider this partially complete table of blood groups and the antigens and antibodies found within blood. Blood group: A, B, AB, and blank. Antigens: A, B, blank, and not applicable. Antibodies: anti-B; anti-A; not applicable; and anti-A, anti-B. What is the missing blood group? And what are the missing antigens?
Let’s start by reviewing some of the key terms in this question. Blood groups are determined by the antigens on an individual’s red blood cells. We may remember that an antigen is a substance that can trigger an immune response. And this includes the proteins on the surfaces of many cells. The antigens on cell surfaces, function in cell identification or in helping an individual’s immune system determine whether a cell belongs in the body or might be some outside potentially pathogenic or disease-causing cell.
In humans, red blood cells can have A antigens, B antigens, a combination of both A and B antigens, or neither of these antigens present on the surface of the cell. An individual that has only A antigen present on the surface of their red blood cells, we say belongs to blood group A. Those with only B antigens present on the surface of their red blood cells, we say belong to blood group B. Those with both A and B antigens present, we identify as belonging to blood group AB. And individuals that have neither of these antigens on the surface of their red blood cells, we identify as belonging to blood group O.
In general, an individual’s immune system will build antibodies against any antigens that are not self or do not originate in that individual’s own tissues. So likewise, individuals will build antibodies against the antigens that do not appear on their own red blood cells. So blood group A individuals will build antibodies against the B antigen, which we call anti-B antibodies. Likewise, blood group B individuals will build anti-A antibodies. Those with blood group AB have both A and B antigens on their own red blood cells, so these individuals will not build antibodies against either of these two antigens. Those in blood group O, on the other hand, have neither A nor B antigens on their own red blood cells. So they will build both anti-A and anti-B antibodies.
Let’s look at the chart we were provided with in this question. First, we’re asked about the missing blood group. The blood groups we just mentioned are A, B, AB, and O. And the blood groups in the chart are A, B, and AB. So the missing blood group is O. This also makes sense if we look at the rest of the chart, since we know that those with blood group O have neither A nor B antigens on their red blood cell surface. So we could say that there are no antigens or that the antigens are not applicable. We also know that since these individuals do not themselves produce the A or B antigens, that they will produce anti-A and anti-B antibodies.
Let’s look at the second question. What are the missing antigens? If we look at the chart, it lists that blood group A produces the A antigen, blood group B produces the B antigen, and then for blood group AB, we have a blank. Blood group AB individuals produce both the A and B antigen on the surface of their red blood cells. So the missing antigens for blood group AB are A and B. This also makes sense looking at the remaining column of the chart because only if an individual produces both A and B antigen will that individual not produce antibodies against either of those antigens.
