Scientists figure out why foetus is not rejected

June 10th, 2012 - 3:39 pm ICT by IANS  

Washington, June 10 (IANS) An important discovery seems to answer a question that has long perplexed scientists - why a mother’s immune system does not reject a developing foetus as foreign tissue.

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, leaving the developing foetus unharmed.

“Our manuscript addresses a fundamental question in the fields of transplantation immunology and reproductive biology, namely, how do the foetus and placenta, which express antigens that are disparate from the mother, avoid being rejected by the maternal immune system during pregnancy?” explained lead investigator Adrian Erlebacher.

“What we found was completely unexpected at every level,” added Erlebacher, associate professor of pathology and a member of the New York University Cancer Institute’s Langone Medical Centre, the journal Science reports.

A central feature of the body’s natural immune defense against transplanted foreign tissues and pathogens is the production of chemokines, according to a New York statement.
The chemokines recruit various kinds of immune cells, including activated T cells, which accumulate and attack the tissue or pathogen.

During pregnancy however, the foreign antigens of the developing foetus 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.

Several years ago, Erlebacher and his research team found that T cells, poised to attack the foetus as a foreign body, were somehow unable to perform their intended role.

They wondered whether there was a barrier preventing the T cells from reaching the foetus. They focused on decidua, the specialized structure that encases the foetus and placenta, and there, in a mouse model, they found new answers.

Researchers then discovered that the onset of pregnancy causes the genes responsible for recruiting immune cells to sites of inflammation to be turned off within the decidua. Consequently, T cells are not able to accumulate inside the decidua and therefore do not attack the foetus and placenta.

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