If Rh- mother has Rh+ baby, the mother can become sensitized during first pregna
ID: 36073 • Letter: I
Question
If Rh- mother has Rh+ baby, the mother can become sensitized during first pregnancy and then if subsequent fetuses are also Rh+, there can be eryhtroblastosis foetalis.
I read that if mother is O- and baby is any +ve blood group other than O+ , then mother will not become sensitized during first pregnancy because a and b antibodies present in her blood will attack the antigen present on the fetus RBC and there will be no time for the mother to synthesize antibodies against Rh.
My Question : Can't the same logic be applied to all other blood groups? For example : A- mother and B+ baby.
Explanation / Answer
if mother is O-
That means:
group O in ABO system: anti-A and anti-B antibodies
group Rh- in Rh system: no D antigen and no ant-D antibodies unless previously senzitized
baby is any +ve blood group other than O+
ABO system: A, B or both antigens present
Rh system: D antigen present
So, the mother has anti-A and anti-B antibodies and her immune response will be directed towards the fetal RBCs containing A, B and D antigens. But, in theory, the immune system should also produce anti-D antibodies because of antigen presenting cells which will expose D antigens to T lymphocytes.
What is known is that if the mother already has anti-D antibodies, no other are secreted from fetal D antigens. This is how passive immunization vaccines work:
This is done so that the fetal Rhesus D positive erythrocytes are destroyed before her immune system can discover them. This is passive immunity and the effect of the immunity will wear off after about 4 to 6 weeks (or longer depending on injected dose) as the anti-Rh antibodies gradually decline to zero in the maternal blood [1].
But the mechanism is not clearly understood:
The most fascinating aspect of the story scientifically is that we still do not have a complete, mechanistic understanding of how this therapy works. The original hypothesis that Rh-immune globulin functions by clearing fetal Rh(D)-positive red blood cells from the maternal circulation, thereby hiding this foreign antigen from the maternal immune system, is inconsistent with the fact that passive immunization with Rh-immune globulin guides the fetal red blood cells directly to antigen presenting cells, the same cells responsible for initiating an immune response to foreign antigens