Maternal exposure to air pollution during pregnancy may alter fetal immune development, according to a study from investigators at the University of California, Davis.
The study, published in Environmental Health by lead author Caroline Herr and COEH co-authors Irva Hertz-Picciotto and Kent Pinkerton, found significant associations between polycyclic aromatic hydrocarbons (PAHs), a component of particulate air pollution, and increases in T lymphocytes (CD3+ and CD4+), as well as decreases in B lymphocytes (CD19+) and natural killer (NK) cells in cord blood during early gestation. In contrast, PAH exposure during late gestation was significantly associated with decreases in CD3+ and CD4+, and increases in CD19+ and NK cells. The relationship between particulate matter less than 2.5 micrograms per cubic meter (PM2.5) and T lymphocytes displayed similar results, though findings were not consistently significant.1
T and B lymphocytes, which are part of the adaptive immune response system,2 begin to develop during the early weeks of fetal development.3 Exposure to high levels of air pollution during critical stages of gestation4 could possibly lead to a greater susceptibility to infection in early life, notes Pinkerton.
Researchers recruited 1,397 pregnant women from May 1994 to March 1999 residing in two districts of the Czech Republic: industrial Teplice in Northern Bohemia where air pollution levels are typically higher and Prachatice in Southern Bohemia, an area with light industry and better air quality.
"During the period these women were pregnant, ambient air was monitored in each of the two cities," explains Pinkerton. These air measurements were then matched to time periods of gestation for each participant, specifically, to each month of pregnancy.
"We found the impact to the lymphocyte population type and abundance had a strong correlation with the type of air quality during each period of gestation," said Pinkerton, suggesting it's plausible the changes were environmentally induced.
In a separate study, the investigators found that concentrations of PAHs and PM2.5 were associated with prenatal changes in cord serum Immunoglobulin (IgE) levels, and that the changes were linked to gestational windows of exposure. 5
The study analyzed IgE levels following 459 births from the same cohort of pregnant women in the Czech Republic. Scientists matched the IgE measurements to PAH and PM2.5 samples from Teplice and Prachatice and assigned them to participants for each gestational month.
Regression models used to estimate prevalence ratios of elevated IgE took into account factors that may influence the results, such as the district of residence, year of birth, maternal IgE and gestational season.
Higher PAHs and PM2.5 exposures during the first trimester, especially in the second month of gestation, resulted in a lower prevalence of elevated cord serum IgE. They also found exposures during mid-pregnancy were associated with a higher prevalence of elevated cord IgE. The associations were stronger among infants whose mothers had low IgE. 6
"This latter finding would appear to support the notion that those without a genetic predisposition to atopy may actually be more susceptible to influences from pollutants in ambient air," noted Hertz-Picciotto.
"The primary risk of elevated IgE levels is susceptibility to allergies or to developing an asthmatic like condition," says Pinkerton, who cautions its uncertain whether the changes they observed in the study could lead to these susceptibilities in childhood.7
Rakesh Ghosh, a postdoctoral fellow in Dr. Hertz-Picciottos laboratory commented: "Overall, these two studies suggest that during fetal life, development of the immune system is not necessarily protected by the placental barrier from environmental insults such as air pollutants."
Hertz-Picciotto adds, "What remains to be elucidated is whether alterations in the maturation of lymphocytes might have long-lasting impact on the ability to appropriately regulate responses to infection."
1,3,4 Herr CE, Dostal M, Ghosh R, Ashwood P, Lipsett M, Pinkerton KE, Sram R, Hertz-Picciotto I. Air pollution exposure during critical time periods in gestation and alterations in cord blood lymphocyte distribution: a cohort of livebirths. Environmental Health. 2010 Aug 2;9:46.
5-7 Herr CE, Ghosh R, Dostal M, Skokanova V, Ashwood P, Lipsett M, Joad, JP, Pinkerton KE, Yap PS, Frost JD, Sram R, Hertz-Picciotto I. Exposure to air pollution in critical prenatal time windows and IgE levels in newborns. Pediatr Allergy Immunol. 2011 Feb;22(1 Pt 1):75-84.
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