Children with asthma are more likely to wheeze as air pollution increases, even when concentrations are within National Ambient Air Quality standards, reports Jennifer Mann in a new study from UC Berkeley. And two subgroups of asthmatic children — those allergic to cats or fungal spores and young boys with mild, intermittent asthma — appear to be the most vulnerable to changes in air quality.
The study published in Environmental Health Perspectives also found that wheezing, a sign of asthma severity, was significantly associated with short-term exposures to nitrogen dioxide and PM10-2.5, which are inhalable, coarse air pollution particles composed of non-exhaust vehicle emissions such as tire rubber, brake fragments and dust. Coarse particles can have biological substances such as pollen, fungi and endotoxin on their surfaces.1,2
“Researchers have focused on the effects of particles in the fine fraction, which means 2.5 microns in diameter or smaller. But there have been fewer studies that have shown health effects of larger particles that are still respirable,” said lead author Jennifer Mann.
“There might be a relationship between the coarse particle findings and allergens that are contained in the coarse fraction of particles,” she notes. “Our research is supportive of previous studies that show fungal antigens make people more responsive to air pollution.”
Mann is a co-investigator with the Fresno Asthmatic Children’s Environment Study (FACES), an epidemiological investigation conducted by researchers at UC Berkeley and funded by the California Air Resources Board (ARB) and the National Institutes of Health (NIH). Starting in 2000, they enrolled approximately 300 asthmatic children from ages 6 to 11 years to examine the effects of air pollution on the health of their lungs.
FACES is led by Ira Tager, a professor of Epidemiology in the School of Public Health at UC Berkeley. Other co-investigators include Katharine Hammond, professor of Environmental Health Sciences (EHS) and John Balmes, director of COEH and professor of Medicine in the Division of Occupational and Environmental Medicine at UCSF and EHS at UC Berkeley.
Fresno has some of the highest levels of air pollution in the United States. During 2005-07, residents were exposed to annual average fine particulate matter concentrations that exceeded national standards by over 40%.The lifetime prevalence of asthma for children 5 to 17 years of age was almost 34% in 2005, nearly double the rate of 18% for the state of California.3
“The purpose of the study was to look at how the relationship of long-term exposures to air pollutants was associated with lung function growth and changes in asthma severity over time. But we were also interested in understanding how short-term changes in air pollution concentrations over the past few days to the past two weeks affected short-term changes in lung function and symptoms,” said Mann.
“We also hypothesized when FACES began that there would be certain subgroups of asthmatic children who would be especially responsive to air pollution, and indeed there were,” said Mann. “Our study will provide answers about vulnerable populations for the ARB’s next review of air quality standards.”
Co-authors on the article include Tager, Balmes, Hammond and Kathleen Mortimer, an adjunct professor of Epidemiology in the School of Public Health at UC Berkeley.
Ira Tager and colleagues recently published a separate study in the Journal of Allergy and Clinical Immunology that explains how air pollution impairs lung function by depressing regulatory T (Treg) cells, which are critically important in regulating immune responses involved in asthma.
They estimated children’s daily air pollution exposure to a group of chemicals called polycyclic aromatic hydrocarbons (PAHs), which are hypothesized to be one of the biologically plausible agents behind observed health effects. They compared these pollution levels to the function of regulatory T-cells in children with and without asthma living in Fresno, and a comparable group of children living in Palo Alto, California, where the air is cleaner.
“Living in a more polluted environment in Fresno was associated with much greater depression of regulatory T-cells and their function, and this depression was associated with immune responses that are enhanced with air pollution exposure,” said Tager. “The degree of suppression of these cells was associated with the severity of the asthma of these children and the decline in their lung function.”
The study presents strong evidence that impaired T-cell function is environmentally induced. Tager adds, “We were able to trace from the air pollution exposure, to the suppression of the function of a very important regulatory cell in the immune system, to phenotypic characteristics of the immune response to asthma, to phenotypic characteristics of the subjects themselves, and a specific alteration of the function of the gene that produces an important protein necessary for the function of Treg cells. As far as we know, we haven’t seen any studies that have made this complete picture.”
The authors note that T-cells may play a role in other autoimmune disorders, suggesting the implications of this study could extend beyond asthma.4 “T-cells are critically important to normal pregnancy,” says Tager. “Studying these cells might provide a unifying mechanism of how air pollution can both affect the risk of asthma and potentially other allergic diseases, and also have effects on birth outcomes.”
Kari Nadeau, an assistant professor in the Division of Immunology and Allergy at Stanford University, is lead author on the paper. COEH faculty Katharine Hammond and John Balmes are co-authors along with Tager.
The new Center for Environmental Public Health led by principal investigator Ira Tager was awarded a $1.5 million, 3-year formative grant from NIH to corroborate their findings in a larger study with research partners at Stanford University.
“The grant will help us understand how air pollution and bioaerosols in the San Joaquin Valley, California, are related to asthma, regulatory T-cell function and adverse birth outcomes: small for gestational age, term low birth weight and structural birth defects,” reports Tager.
NIH awards these grants to develop the infrastructure needed for a full Children’s Health Center. UC Berkeley has two other Children’s Health Centers — one led Brenda Eskenazi and another led by Pat Buffler.
1 The Health Effects of Coarse Particulate Matter, Air Resources Board of the California Environmental Protection Agency.
2 Mann JK, Balmes JR, Bruckner TA, Mortimer KM, Margolis HG, Pratt B, Hammond SK, Lurmann FW, Tager IB. Short-term effects of air pollution on wheeze in asthmatic children in Fresno, California Environ Health Perspect. 2010 Oct;118(10):1497-502.
3 Nadeau K, McDonald-Hyman C, Noth EM, Pratt B, Hammond SK, Balmes J, Tager I. Ambient air pollution impairs regulatory T-cell function in asthma. J Allergy Clin Immunol. 2010 Oct;126(4):845-852.
4 Press release by Sarah Yang, Media Relations at UC Berkeley
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