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Pollution's links to asthma, allergy: airborne PAH tied to disabled immune-regulating cells.

Bad actors in air pollution may contribute to asthma and allergy by subverting protective cells in the body that tone down immune reactions, researchers report. The pollution components also seem to rev up overactive immune warriors--already linked to allergies--that need no such prompting.

The airborne culprits are polycyclic aromatic hydrocarbons, or PAHs, the products of incomplete burning of fuel in diesel engines, furnaces, wood fires, wildfires and even barbecue grills. Past research has tied air pollution to asthma and allergy, but the link between PAHs and these immune problems is still unclear.

In the new study, researchers found that children exposed to high levels of PAHs had poorly functioning T-regulatory cells, or T-regs, which normally ratchet down immune-caused inflammation as needed.

"T-regs are peacekeeper cells," said Kari Nadeau, a physician and biochemist at Stanford University who presented the findings February 23. "But in asthma, T-regs are impaired."

The team also found that kids exposed to a lot of PAHs made excess amounts of an antibody called immunoglobulin E, or IgE. The IgE antibody normally helps the body fight parasites. But in developed countries, where parasitic infections are largely a thing of the past, IgE has become better known for its role in allergy. The body often cranks out IgE as part of a misguided immune reaction against noninfectious substances in the environment. IgE also shows up in asthma, which can be triggered by allergy.

To study the effect of air pollution on these immune players, Nadeau and her colleagues obtained blood tests, lung function readings and health information from 153 children with a median age of 14 in Fresno, Calif. The researchers sampled airborne PAHs to estimate exposure, and chose Fresno because of its relatively high air pollution levels.

Children with high exposure to PAHs, based on air sampling in and around their homes, made high amounts of IgE and had lower T-reg function than children exposed to low levels. High PAH exposure during the most recent three months was linked to 51 percent higher risk of being diagnosed with asthma.

"This is a very interesting and thought-provoking study," said Todd Rambasek, an allergist at ENT and Allergy Health Services in Lorain, Ohio. He said that other studies that had linked air pollution with asthma and allergy had failed to distinguish between PAHs and other pollutants that could contribute to the conditions, such as ozone or particulate matter.

Nadeau also reported that consistent PAH exposure coincided with changes in a gene called Foxp3.

As reported by Alexander Rudensky of Memorial Sloan-Kettering Cancer Center and colleagues in Nature in 2010, Foxp3 seems to be a master regulator of T-reg populations in the body. Unfortunately, Nadeau said, the changes observed in Foxp3 seem irreversible and widespread.

The asthma rate is 22 percent among children in Fresno, Nadeau said; the CDC estimates the rate for the United States as a whole is 9.5 percent. Up to 70 percent of people in Fresno have an allergy, she notes, more than double California's average lifetime risk of having an allergy.

The new study adds PAHs to a known pollution problem in the area: In 2012, the American Lung Association ranked Fresno fifth-worst among California cities for overall particulate pollution.
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Title Annotation:Health & Illness; polycyclic aromatic hydrocarbons
Author:Seppa, Nathan
Publication:Science News
Geographic Code:1USA
Date:Mar 23, 2013
Words:535
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