Question

Human blood types A, B and O are associated with the carbohydrate antigens A, B and H respectively. A and B antigens are caused by an alteration of H antigen. Normally everyone can synthesize H antigen (a cell surface carbohydrate found on red blood cells and other cell types). Some people make A and/or B transferase(s) which converts the H antigen to an A and/or B antigen respectively. The H antigen is produced by a specific fucosyltransferase encoded by the FUT1 gene. The A and/or B transferase(s) are encoded by the gene ABO glycosyltransferase. If you have the A allele you add an "A" sugar molecule to the original H molecule (H antigen) which converts it into the A antigen (Type A blood), if you have the B allele you add a "B" sugar (B antigen; Type B blood), if you are a heterozygote (A and B allele) you add the "A" sugar to some H molecules and the "B" sugar to others (A and B antigen; Type AB blood). People with the O allele cannot make a functional transferase and therefore the H antigen remains unaltered (stays H antigen; Type O blood). Very rarely individuals are born with a homozygous mutation in FUT1 that prevents them from producing H antigen. If they cannot produce H antigen then regardless of genotype at ABO glycosyltransferase they cannot produce A and/or B antigen either. In other words, they lack H, A and B antigens. This is called the Bombay phenotype. The quickest and easiest way to test someone's blood type is to mix a few drops of their blood with anti-A or anti-B antibodies and observe the reaction. If the blood reacts to the anti-A antibodies then the blood contained A antigen (Type A), if it reacts with the anti-B antibodies then it contained B antigen (Type B) and if it reacts with both then the blood contained A and B antigens (Type AB). If the blood did not react with either anti-A or anti-B antibodies then it did not contain A or B antigens (Type O). You can check out this Blood Typing Game if you want to see some examples of, and explore these, tests. You are running a blood donation clinic and you are testing a donor's blood type. You have a testing plate with three wells in front of you. All the wells have some clear liquid in them. One well contains anti-A antibody, one well has anti-B antibody and one is a control well. The control well does not have antibody of any type in it. You prick the donor's finger and squeeze out a few drops of blood into each well. If the antibody in the well reacts with the blood (antibody binds antigen on the blood) the blood will agglutinate (clump). Though neither you nor the donor know it, the donor has the Bombay phenotype. Would you expect to see agglutination/reaction in the following (answer yes/no)? • anti-A antibody well • anti-B antibody well • control well Based on your test results alone what blood type would you say the donor has? Since you have no way of knowing the donor has the Bombay phenotype, what type of ABO antibodies (anti-A, anti-B, anti-H) would you expect someone with this blood type to produce? (note: this is different then asking what their blood reacted with, this isn't the antigen on the surface of the blood, this is the antibody they produce; you may want to revisit the previous question or check out this page from Canadian Blood Services) Blood typing using the agglutination reaction above tests for the presence of antigen on the blood cell surface. If instead you were to test for the ABO antibodies a person makes what would you find in a donor with the Bombay phenotype (note: in the question above you did not know they had the Bombay phenotype, this time you do)? (In other words, would you expect to see anti-H, anti-A and/or anti-B antibodies in an individual with the Bombay phenotype?) Do the antibodies present in your donor with the Bombay phenotype match those expected from the blood typing result using the agglutination test? Why or why not?

Answer 1

1. There will be no agglutination either in the anti- A antibody well, the anti - B antibody well nor the control well.

2. Based on this test we may be forced to assume that the donor had Blood type O.

3. We will assume that since it is O blood type that it will contain both anti - A and anti - B antibodies.

4. When testing for antibodies in a person with Bombay phenotype we would find A, B and H antibodies.

5. The anitbodies present in the donor with Bombay phenotype, will it match those expected from the blood typing result using the agglutination test? No it will not match because the normal agglutination test will not show the presence of H antibody.

Only if we do a specific test for H antigen can we detect the Bombay blood group otherwise it will only be read as Blood type O.