Hi 

Just wondering if only one does of proph D given to  Partial D woman, wouldn't it   consumed by partial D woman?  How will it help to prevent Rh D immunisation in this pregnancy. ?

I am by no means an expert on the topic, but I think that since Rhogam is human-derived and therefore polyspecific, it seems as though there is a possibility that the product contains antibodies to multiple D epitopes and would therefore be able to bind to whatever antigen is present on the fetal RBCs that Mom lacks.  

 

Im not familiar with all of the brands of RhIg though, I don't know if that is true for the others.

I agree entirely with you Heather, although I do know that some people do give a double dose.  I've never quite understood the thinking behind this double dose because, as you say, the antibody to the epitopes the mother lacks would still be in her circulation in the amounts and concentrations that would be expected from a single dose.

Isn't the thought that the antibody would not be in mom's circulation because it is all bound onto her own Rh pos RBCs?  I wonder if the Fc portion of the antibody works quite effectively attached to mom's RBCs to dampen the immune response just as it would if attached to the baby's RBCs.  I can't say I am an expert on what they think the mechanism of RhIG is these days.

No Mabel, as Heather says, polyclonal anti-D is a whole soup of anti-D specificifities that will be able to bind to all the thirty or so different epitopes that are expressed when the normal D antigen is present.

When a partial D is present, some of those epitopes will be missing (not expressed) on the red cell, and the anti-D specificities that are directed against those missing epitopes will remain free - and, thus, will be able to bind onto the foetal red cells, if they express a normal D antigen.

If you like, think of it as alphabet soup.  You eat all the bits of alphabet from A to, oh, I don't know, let's say T, as you are a red cell expressing a Partial D antigen, but you do not eat (express) epitopes U to Z.  Along come some red cells from your baby, and your baby is a red cell expressing ALL of the normal D epitopes, Your baby will then be able to eat (be sensitised by) the letters U to Z in the soup (assuming it is on solids, of course)!!!!!!!!!!!  The immune system will be able to recognise a red cell that has eaten letters U to Z and will destroy these red cells IN the RES.