Mother's Immune System Does Not Reject Developing Fetus as Foreign Tissue...

Why Mother's
Immune System Does Not
Reject Developing Fetus as Foreign Tissue...

The researchers discovered that
... embryo implantation sets off a
process that ultimately turns off a
key pathway required for the
immune system to attack foreign
bodies. As a result, immune cells
are never recruited to the site of
implantation and therefore
cannot harm the developing fetus.

A central feature of the body's
natural immune defense against
transplanted foreign tissues and
pathogens is the production of
chemokines as a result of the local
inflammatory response. The
chemokines recruit various kinds
of immune cells, including
activated T cells, which accumulate
and attack the tissue or pathogen.
The chemokine-mediated
recruitment of activated T cells to
sites of inflammation is an
integral part of the immune
response.

During pregnancy however, the
foreign antigens of the developing
fetus and the placenta come into
direct contact with cells of the
maternal immune system, but fail
to evoke the typical tissue
rejection response seen with organ
transplants.

Specifically, they revealed that
the implantation of an embryo
changes the packaging of certain
chemokine genes in the nuclei of
the developing decidua's stromal
cells. The change in the DNA
packaging permanently
deactivates, or "silences," the
chemokine genes. Consequently,
the chemokines are not expressed
and T cells are not recruited to the
site of embryo implantation.

These findings give insight into
mechanisms of fetal-maternal
immune tolerance, as well as
reveal the epigenetic modification
of chemokine genes within tissue
stromal cells as a modality for
limiting the trafficking of
activated T cells.

This is a very exciting finding for
us because it gives a satisfying
explanation for why the fetus isn't
rejected during pregnancy, which
is a fundamental question for the
medical community with clear
implications for human
pregnancy.