WASHINGTON Women being urged to breast-feed their babies got another reason last week -- researchers said they found breast milk stimulates the immune system in a way not seen before.

They said breast milk is rich in a kind of protein called soluble CD14, which in turn stimulates the development of B cells. B cells are immune cells made in the bone marrow and key to the production of antibodies.

"We have known for 100 years of the benefits of breast feeding," Dr. Michael Julius of the University of Toronto and the Toronto Hospital, who led the study, said in a telephone interview.

"Over the last decades the scientific basis for this conventional wisdom has increased due to our identification of many of the elements of breast milk that mediate all these good things. In addition to being full of nutrients, in addition to being full of growth factors, it is full of things that protect the newborn."

For instance, doctors knew that nursing mothers could pass on antibodies to their babies. Antibodies are the protein flags of the immune system -- they identify and home in on invaders such as bacteria and viruses, flagging them for immune cells to attack.

The key to their success is their diversity. The more different kinds of antibodies the body has, the higher the number of enemies it can fight off.

Researchers had known about soluble CD14 but all its functions were not apparent, Julius said.

"This is the first demonstration of this biological activity of the molecule and the fact that it is so extraordinarily enriched in mammary secretions," he said.

"Because it is able to directly activate B cells, it provides active protection to the baby. We imagine it functions to kick-start the baby's immune system."

The researchers, who included teams at the University of Western Ontario, Osaka University, and Gemma Biotechnology Inc. in Toronto, did their tests on mice.

Writing in last week's issue of the proceedings of the National Academy of Sciences, they said CD14 caused the B cells from the mice to differentiate -- to grow into different types.

Later tests showed that milk and colostrum -- the first rich secretions from a mother's milk glands -- was rich in CD14. This was true of both cows and people, they found.

Advocates of breast-feeding say breast-fed babies are more intelligent and healthier than babies fed bottled milk. Scientific studies tend to support this, although the differences between breast and bottle-fed babies are subtle.

(Reuter)