Children's Immune System
May Be Influenced in Womb
Excerpt By Melissa Schorr, Reuters Health

NEW YORK (Reuters Health) - The rigor of a child's immune system could be established before birth, say investigators who believe that the prenatal environment may play a role in whether or not an infant becomes more or less susceptible to asthma and allergies later in childhood.

Previous research has found that first-born children or those who have few siblings are more likely to have asthma and allergies than those with many siblings. Many researchers have suggested this may be due to the ``hygiene hypothesis'': children with many siblings are more exposed to germs early on and develop stronger immune systems, while children who are first-born or only children do not receive this benefit.

However, researchers suggest that the prenatal environment may also play a role in the infant's developing immune system. ''The question was: is this happening after birth, or is this happening before birth?'' Dr. Wilfried Karmaus, an associate professor or epidemiology at the Michigan State University in East Lansing, Michigan told Reuters Health.

Karmaus and colleagues hypothesized that a change in the mother's body between her first and later pregnancies can cause a shift in the womb that affects the child's immune system.

``There may be changes in the endocrine response in the first pregnancy different from second and third pregnancy,'' he explained.

For example, endocrine disruptors--such environment-contaminating chemicals like PCBs--may be higher during a woman's first pregnancy because the chemicals are released during breast-feeding and each subsequent pregnancy. The woman's vulnerability to infections during each pregnancy may also play a role, he suggested.

To explore that association, the researchers looked at nearly 1,000 infants born on the Isle of Wight in England between 1989 and 1990. They tested the infant's umbilical cord blood for levels of immunoglobulin E (IgE), an antibody linked to allergies.

In their report, published in the November 15th issue of the American Journal of Epidemiology, the researchers note that first-born children were twice as likely to have a higher concentration of IgE, with 16% of first-born children having a certain level of IgE compared with only 8% of third-born children.

The research team conducted a skin prick test--an allergy test--on the children at age 4 and found that those with higher levels of IgE did show a significant increase in allergic reactions. However, they did not find a direct correlation between birth order and skin allergic reactions.

``We have to move our explanation from postnatal to prenatal,'' Karmaus noted. ``The sibling effect may have its origin in utero.''

SOURCE: American Journal of Epidemiology 2001;154:909-915.

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