What prevents maternal antibodies to act against fetus?

[nipun]

Please reply within an hour,

I need to know why the maternal antibodies dont act against fetal membranes/fetus or if they do ,what opposes them. The Trophoblast? and how ?
although fetus is separated from mother and there is rarely any blood mixing, still the fetal membranes are in direct contact with the mother.and what would happen if the antibodies somehow cross the barrier. will they act against the fetus then?

1 last question'
what in an antigen causes the antibody production. reply soon...thanks..

[Navin]

Due to my limited knowledge I am unsure why the antibodies do not attack the foetus. (maybe genetics or maybe hormones?)
However I know that some antibodies from the mother actually enters the foetus (yes, they pass through the barrier). The antibodies help to prevent the foetus form infection and the antibodies also continue to linger in the baby for a while after he/she is born.

[MrMistery]

first of all, only some classes of imunoglobulines can cross the placenta, not all.
Now, i saw a documentary on national geographic a while back, i think some hormones prevent this from happening. If i am wrong please correct me if i am wrong.

[Dr.Stein]

We should know that our immune system has an ability to recognize between self and nonself substances. Maternal antibodies will not attack fetus because they recognize it as self, thus generating immune tolerance. However if they (maternal antibodies) find appropriate antigen(s) against them, they will attack them. For instance in rhesus case.

The immunosurveillance system is the one who responsible with the invading antigens. This system including WBC and APC which helps to elliminate foreign substances to recognize between self and nonself substances, so the effector cells will not wrongly attack self cells, in this case fetus.

And yes, fetal membranes are important to filter maternal envirnoment (as a barrier) to provide a strong immune system against things that should not happen.

[victor]

We should know that our immune system has an ability to recognize between self and nonself substances.

it need a while till the mother's immune system will recognize the fetus as a self....within that period, estrogen will be secreted as an immunosuppresive agent against the mother's own immune system (usually for the specific one which is T-cell).

[Poison]

IgA can pass through placenta

[Dr.Stein]

We should know that our immune system has an ability to recognize between self and nonself substances.

it need a while till the mother's immune system will recognize the fetus as a self....within that period, estrogen will be secreted as an immunosuppresive agent against the mother's own immune system (usually for the specific one which is T-cell).

Yes, and it is how "the morning sickness" initiated

[MrMistery]

Estrogen? I would think that progesteron, since the secretion of progesteron is high in the first 3 months of pregnancy

[Dr.Stein]

Nah, it's estrogen. Estrogen is also secreted during pregnancy but the level is low, you know the feedback mechanism between estrogen and progesteron.. If the level of estrogen cannot be kept low, one of the result is abortus, because estrogen will lead uterine to contract.

In morning sickness case, the queasy feeling is the result of estrogen and immune system to reject the new stuff inside uterine, but then it leads to tolerance since immune system recognizes it as self that doesn't need to attack so that the baby is safe and the mom is better.

[victor]

Sometimes..I also have the morning sickness....sometimes I have it as a GI syndrome..

[MrMistery]

you might be pregnant victor

[Dr.Stein]

Aww Victor could be hermaphrodite