Parasitic trick helps fetus avoid attack
- Parasitic trick helps fetus avoid attack
* 03 November 2007
* NewScientist.com news service
* Andy Coghlan
IF YOU think comparing a fetus to a parasite is unkind, think again.
The puzzle as to why a pregnant woman's immune system doesn't attack
the fetus and placenta - both of which contain genetic material from
the father - may finally have been cracked.
It seems the placenta produces hitherto unknown hormones containing
the same molecule some parasitic worms use to avoid detection by the
immune system. As well as helping the fetus avoid immune attack, the
hormones may also summon extra blood and nutrients to the aid of an
“The placenta produces hormones containing the same molecule that
some parasitic worms use to avoid the immune system”
The discovery of this possible chemical control system could herald
new ways to prevent recurrent miscarriages and pre-eclampsia, a
condition which can lead to convulsions, coma and death in pregnant
women. It also sheds some light on why rheumatoid arthritis, an
autoimmune disease, eases when women become pregnant.
The placental hormones have avoided detection until now because they
are virtually identical to neurotransmitter chemicals that convey
signals in the brain and nervous system. But adding a molecule called
phosphocholine changes their function completely.
"When the penny finally dropped, it was very exciting," says Philip
Lowry of the University of Reading, UK. Analysing fresh placental
tissue from women and from female rats, his team found phosphocholine
attached to the neurotransmitter neurokinin B and to the precursor of
another neurotransmitter called hemokinin (Journal of Molecular
Endocrinology, DOI: 10.1677/JME-07-0007).
Other researchers warn that extensive work is needed to establish
exactly what the phosphocholine-linked hormones do. "It isn't shown
in this study that these molecules have any functions whatsoever,"
notes Anne Croy of Queen's University in Kingston, Ontario, Canada,
who studies miscarriages.
Based on parasites' successful use of phosphocholine as a "cloaking
device", Lowry thinks its main function in pregnant women is to hide
the placenta and the fetus from the immune system. His previous
research, which links pre-eclampsia to neurokinins, suggests that
high levels of the placental version of neurokinin B might have an
additional function - acting as a distress signal for an underfed or
struggling fetus. By obtaining extra blood and nutrients for the
fetus, Lowry says, the hormone might somehow trigger pre-eclampsia -
the precise cause of which is unknown. Ultimately, Lowry hopes to use
drugs based on phosphocholine as a new way to prevent miscarriages,
which may result from an overactive immune system. The finding may
also enable more benign immunosuppressant drugs to be developed for
rheumatoid arthritis, he says.
From issue 2628 of New Scientist magazine, 03 November 2007, page 16