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Wednesday, 6 February, 2002, 23:58 GMT
Sex 'primes woman for sperm'
Women 'get used' to men's sperm
Women 'get used' to men's sperm
Regular sex with the same man may prime a woman's immune system not to reject his sperm when they try to conceive, scientists suggest.

The theory could partly explain why humans have sex even when they aren't trying for a baby.

Even a year before conception, exposure to sperm, either through intercourse or other sex acts, can have protective effects against problems ranging from infertility to miscarriages and high blood pressure during pregnancy.

Researchers from the University of Adelaide in South Australia say previous studies have suggested it could also guard against the life-threatening condition pre-eclampsia - where the mother's body rejects the placenta.

Eventually when the woman conceives, her [immune] cells will say, 'we know that guy, he's been around a long time, we'll allow the pregnancy to continue'.

Gustaaf Dekker, University of Adelaide
All these problems could to be linked to a failure of the mother's immune system to accept the foetus and placenta which both contain "foreign" proteins from the father's genes.

If the placenta, which supplies oxygen and nutrients from the mother's blood to the foetus, is damaged it can result in a baby that is underweight or stillborn.


The process of accepting foreign cells is called immune modulation.

After intercourse, a woman's immune system sends cells to the cervix to collect the father's foreign proteins to take back to the lymph nodes so that other immune cells can recognise them.

The Adelaide team suggests semen contains an agent which prompts the woman's immune system to accept it.

Sometimes, this process fails and women can have a severe immune response, which could be as serious as anaphylactic shock.

The agent is transforming growth factor TGF-beta.

Studies in mice showed TGF-beta switches what would usually be a hostile reaction to "foreign" sperm from the immune cells into a friendly one.

Gustaaf Dekker, one of the Adelaide researchers, said: "If there's repeated exposure to that signal then eventually when the woman conceives, her [immune] cells will say, 'we know that guy, he's been around a long time, we'll allow the pregnancy to continue.'"

He added: "We see patients that have two miscarriages, then they finally manage to get through their miscarriage period, and they have pre-eclampsia, or the placenta detaches and they have a stillbirth at 24 weeks."

Future treatment hopes

Dr Dekker also examined the impact of other sex acts on the immune system while working at the Free University of Amsterdam.

He looked at 41 pregnant women with pre-eclampsia and 44 without and found 82% of those without pre-eclampsia practised other sex acts compared with only 44% of those with the disorder.

But other doctors suggest the first group were likely to be having more sex overall.

The Adelaide team are now looking to see if men who have fathered pregnancies which have ended in miscarriages or pre-eclampsia had low TGF-beta levels in their semen.

If the theory is confirmed, women who suffer repeated miscarriages or IVF failures could be given TGF-beta along with the father's foreign proteins, possibly in a vaginal gel during intercourse

The Adelaide team even suggest understanding how a woman's immune system tolerates a foetus for nine months could lead the way to advances in the treatment of autoimmune diseases such as lupus and multiple sclerosis.

But Dr Gulam Bahadur, a consultant clinical scientist in the department of obstetrics and gynaecology at the Royal Free and University College Medical School, told BBC News Online: "The content is interesting and makes attractive reading.

"But from the scientific viewpoint one has to err on the side of caution in interpreting the many diverse and speculative points, simply because there are insufficient controls or appropriately thought out studies."

The research is published in New Scientist.

See also:

24 Oct 01 | Health
Gene key to sperm power
28 Feb 00 | Health
Sperm boost may aid fertility
02 Jul 01 | Fertility conference 2001
DIY sperm test kit developed
27 Nov 01 | Health
Unprotected sex risks young lives
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