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Author Topic: Why don't maternal IgGs attack foetal tissues?  (Read 2651 times)

Offline chris

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Why don't maternal IgGs attack foetal tissues?
« on: 17/11/2013 14:54:59 »
From about 29 weeks gestation, the placenta transfers maternal antibody into the foetal circulation to provide passive protection after the baby is born and before the infant's own immune reponse matures.

We know that the IgGs can attack red blood cells if the mother has been sensitised to the rhesus (D) antigen during a previous pregnancy. So why don't the other maternal IgGs attack other targets on the foetal tissue, which is, after all, half genetically distinct from the mother?



 

Offline RD

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Re: Why don't maternal IgGs attack foetal tissues?
« Reply #1 on: 17/11/2013 15:34:11 »
Apparently because the mother's immune system has not been exposed to the fetal cells ...

Quote from: wikipedia.org/Immune_tolerance_in_pregnancy
... the placenta does allow maternal IgG antibodies to pass to the fetus to protect it against infections. However, these antibodies do not target fetal cells, unless any fetal material has escaped across the placenta where it can come in contact with maternal B cells and make those B cells start to produce antibodies against fetal targets. The mother does produce antibodies against foreign ABO blood types, where the fetal blood cells are possible targets, but these preformed antibodies are usually of the IgM type, and therefore usually do not cross the placenta.
http://en.wikipedia.org/wiki/Immune_tolerance_in_pregnancy#Placental_mechanisms
 

Offline distimpson

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Re: Why don't maternal IgGs attack foetal tissues?
« Reply #2 on: 17/11/2013 17:20:34 »
Apparently because the mother's immune system has not been exposed to the fetal cells ...

There are a few fetal cells in mom, we were pretty excited to learn this way back when and thought of a blood test to replace amniocentesis. Haven't kept up with the research but I don't believe anything panned out. It's a very small number, perhaps not enough to give an immune response?
Clin Genet. 2001 Feb;59(2):74-9.
Fetal cells in maternal blood.http://www.ncbi.nlm.nih.gov/pubmed/11260204 "Fetal lymphocytes, trophoblasts, and nucleated red blood cells have each been separated from maternal blood by methods such as flow cytometry, magnetic cell sorting, and charge flow separation."

This article gives a little analysis: http://www.sciencedaily.com/releases/2012/06/120606155802.htm "Researchers suspect that fetal cells in a mother's blood stream help her immune system tolerate and not attack the fetus."
 

Offline Lmnre

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Re: Why don't maternal IgGs attack foetal tissues?
« Reply #3 on: 17/11/2013 22:00:04 »
Regarding the mother's immune system contact with non-mother cells, what about it attacking the placenta itself? Certainly it comes into contact with the placenta, right?

The placenta is a very invasive organ, and in an extreme placentation called placenta percreta, it can grow through the uterine wall and into the rectum or bladder, which is obviously life-threatening, and yet the mother's immune system apparently allows it. 
 

Offline RD

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Re: Why don't maternal IgGs attack foetal tissues?
« Reply #4 on: 18/11/2013 01:57:57 »
Regarding the mother's immune system contact with non-mother cells, what about it attacking the placenta itself? Certainly it comes into contact with the placenta, right?

Placenta manufactures a substance which called phosphocholine which suppresses the immune response ... http://news.bbc.co.uk/1/hi/health/7081298.stm
 

Offline CliffordK

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Re: Why don't maternal IgGs attack foetal tissues?
« Reply #5 on: 18/11/2013 07:09:35 »
There can, however, be Rh Disease (incompatibility).

It is a specific case where the mother is Rh Negative, and the father is Rh Positive.  Usually the first Rh Positive child is fine, but the mother can become sensitized to the Rh antigen, and can have a reaction against the second, or later children.

RhoGam (Rho(D) Immune Globulin) is given to almost all Rh negative mothers with Rh positive infants in order to prevent sensitization, and has been effective at preventing the disease.  However, I do remember, perhaps 35 years ago, one of our neighbors had a third child with Rh incompatibility, and the infant required multiple blood transfusions immediately after birth.  Fortunately the child recovered.
 

Offline chris

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Re: Why don't maternal IgGs attack foetal tissues?
« Reply #6 on: 23/11/2013 10:41:45 »
Thanks for these answers, but they don't actually answer the question unfortunately!

The issue is that maternal antibody is transferred to the foetus during pregnancy; there must, because the baby is 50% genetically distinct from the mother, be antigens on the foetal cells that are paternal in origin. As such, it's likely that the mother must have some antibody, by chance, that will cross react with these epitopes. I can only assume that because only IgG antibody is transferred, the mother won't have clonally expanded any paternally-reacting antibodies (which will be IgM) owing to lack of exposure to those paternal antigen.

If, on the other hand, the woman had been previously exposed to paternal tissues in a transplantation experiment, then she might well have these antibodies and this could cause a problem for the baby...
 

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Re: Why don't maternal IgGs attack foetal tissues?
« Reply #6 on: 23/11/2013 10:41:45 »

 

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