Image for Study links wildfire smoke exposure to reduced immune system function

10-day episode of wildfire smoke in 2008 offers unexpected research opportunity

Sacramento — An ARB-funded study at the California National Primate Research Center showed for the first time that exposure to high levels of fine particle pollution at infancy adversely influences development of the branch of the immune system that combats infectious disease, and adversely affects the development of lung function.

The study was the product of unusually high levels of fine particle pollution in Northern California as the result of about 2,000 wildfires in June 2008. Over a period of 10 days levels of PM2.5 (the terminology for inhalable particles smaller than 2.5 microns) at the UC Davis campus were recorded at 50 to 60 micrograms per cubic meter. Some readings reached as high as nearly 80 micrograms per cubic meter, well over the federal standard of 35 micrograms per cubic meter.

The study was designed to investigate the effects of air pollution on infants, taking advantage of a rare case of scientific serendipity: as it happens, the high levels of particle pollution coincided with the end of the season when rhesus monkey babies are typically born at the federally funded Primate Center. The rhesus macaque monkeys, including a significant number of monkeys between 1 and 3 months old, live full time in outdoor field cages at the facility, and were exposed to the elevated levels of air pollution 24 hours a day as a result of the fires.

The following year, no days came close to exceeding the federal standard, allowing investigators to compare lung function and levels of immune system activation of the 2008 smoke-exposed monkeys to those born in the same months in 2009 when there were no wildfires.

All animals were studied when they were 3 years old (young adulthood). No animals were harmed, and the research involved only blood samples and lung function tests.

The ARB-funded research project, “Persistent Immune Effects of Wildfire PM Exposure During Childhood Development,” was led by Dr. Lisa Miller, CNPRC respiratory diseases unit leader.

Significant findings include:

• Several parameters of immune system function that help protect the body from bacterial infection were found to be reduced in the animals exposed as infants to the wildfire PM2.5, compared to animals born the following year.

• This is the first time fine particle pollution has been shown to influence the branch of the immune system that combats infectious disease.

• Unexpectedly, investigators found a link between reduced immune system function and abnormalities in lung function, particularly in female animals.

The results suggest that, as a result of the adverse impact on the immune system, the exposed monkeys are more susceptible to infectious disease. The results also suggest that infancy is a period during which high PM2.5 exposures may adversely influence development of the innate immune system, and adversely affect development of lung function. Infancy may be associated with increased vulnerability to high levels of air pollution exposure because of the rapid lung and immune system development that occurs during the early months of life.

Researchers intend to continue their research on the two groups of monkeys throughout their lives to see if the adverse immune and lung function impacts persist.

While several studies suggest short-term exposure to wildfire emissions (over a few days) can worsen symptoms of asthma and other lung diseases, no studies to date have investigated whether there are long-term health consequences to such exposures.

Numerous scientific studies have previously linked exposure to PM2.5, which can be deeply inhaled into the airways and lungs, to a variety of problems, including premature death, especially in people with pre-existing heart disease. PM is also found in smog.

The California Air Resources Board has implemented a number of emissions control regulations that have dramatically reduced PM2.5 levels statewide. While the PM2.5 levels measured in summer 2008 are much higher than levels typically seen today, those levels were common in the past, prior to the state implementing emissions control regulations.

For more information about the ARB-funded research project, go to