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Henshaw


saralm88

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Human anti-He is, indeed, rare, but that is also to do with the fact that the He antigen is, itself, rare (so it is less likely to stimulate an antibody), and, or it appears "naturally", we are unlikely to detect it, as our screening cells are highly unlikely to be He+.  In addition, for want of a better way of putting it, although He is a "single" antigen, there are several genetic backgrounds to the He "antigen".

 

So, let's start from the basics.  Like M is the allelomorph to N, He is the allelomorph to 'N'.

 

What then is 'N'?

 

Well, the N antigen always used to be described as the first five amino acid residues (from the NH2 terminal of the molecule) on the Glycophorin A molecule, viz Leucine, Serine, Threonine, Threonine and Glutamic acid, but now is numbered as numbers 20 to 24 because the first 19 amino acid residues are now not known to be part of the mature molecule.

 

Similarly, the first five amino acid residues (now the 20th to the 24th) on  Glycophorin B molecule are normally also Leucine, Serine, Threonine, Threonine and Glutamic acid, and these make up the 'N' antigen.  Although I have said that there are several genetic backgrounds to the He antigen, essentially it is made up of Tryptophan, Serine, Threonine, Serine and Glycine moeity.

 

So, we have now established that the He antigen is very, very rare (according to the FactsBook, 3% in African Americans, up to 7% in Blacks in Natal, and not found in Caucasians), and so, unless the antigen is particularly immunogenic (which it obviously is not - otherwise anti-He would be more common in Blacks in Natal), then the chances of an individual producing an anti-He, and then being transfused with He+ blood is going to be a good deal rarer - which is why there is no real data concerning haemolytic transfusion reactions.

 

Obviously, if a woman produces anti-He as a result of pregnancy, and she gets pregnant by the same male partner again, then (given the frequency of the antigen) there is usually a 50% chance of the second or subsequent baby being He+, and then, of course, the antibody would have to be IgG1 and/or IgG3, would have to be of a titre of 32 or more (usually) and would have to react at 37oC, which would be even rarer, and this is why we also have no data on HDFN.

 

Sorry if this is a bit rambling, but I am also watching the New Zealand versus Georgia match in the rugby world cup whilst writing this!!!!!!!!!!!!!!!!!  I hope I haven't made too many mistakes.

 

:blahblah:  :blahblah:  :blahblah:  :blahblah:  :blahblah:

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