By Megan Brown, American Academy of Allergy, Asthma & Immunology – 11/6/2013
Outside air pollutants are a known trigger of asthma, the most common chronic disease in children according to the World Health Organization, but whether these pollutants actually cause new cases of asthma is still being investigated. Research from the 2013 Annual Meeting of the American Academy of Allergy, Asthma & Immunology (AAAAI) looked
at the effects of polycyclic aromatic hydrocarbons (PAHs) on a sample of children and found that increased exposure to these chemicals in air pollution were associated with certain immune system effects and asthma diagnosis.
“We already know that immunoglobulin E (IgE) plays a role in asthma development and
increased IgE levels result when asthmatics are exposed to triggers like pollutants,” explained senior study author and asthma specialist Kari Nadeau, MD, PhD, FAAAAI. “There is also growing evidence that regulatory T cells, which are a specific kind of cell that modulates the immune system, play an important role in inhibiting allergic sensitization and IgE production after exposure to an allergen. Regulatory T cell numbers are reduced in patients with asthma.”
PAHs are a type of chemical found naturally in the environment although they can also be manmade. They are created when substances such as coal, oil and gas are burned but not completely combusted. A person can be exposed to PAHs through a variety of ways, including vehicle exhaust fumes, wildfires, wood-burning stoves, fossil fuel combustion, barbecued meats and cigarette smoke.
To assess the effects of PAH exposure on the immune system and the occurrence of new asthma cases, asthma specialists and researchers from Stanford University and the University of California, Berkeley studied a sample of children from Fresno, which is known for its high levels of PAH in outside air pollutants.
A total of 332 children between the ages of 10 and 18 were given questionnaires and a lung
function test called spirometry. Statistical analysis was used to calculate PAH exposure levels. For 153 children within the sample, total IgE levels were determined and regulatory T cells separated from blood samples.
From their data, the researchers did see that higher levels of PAH exposure were linked to
increased total IgE levels. Significantly weakened regulatory T cell function was also observed in those children who had been exposed to higher amounts of PAH.
Another interesting discovery was an apparent association between PAH exposure accumulated over the last three months analyzed and the diagnosis of asthma. An asthma diagnosis also appeared to be correlated with total IgE levels. “Further research needs to be done, but what we can hypothesize from our pediatric sample is that exposure to high PAH quantities may be having an effect at the molecular level, possibly leading to new cases of asthma,” concluded asthma specialist Dr. Nadeau.
The AAAAI represents allergists, asthma specialists, clinical immunologists, allied health
professionals and others with a special interest in the research and treatment of allergic disease. Established in 1943, the AAAAI has more than 6,700 members in the United States, Canada and 60 other countries.
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