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The study focused on two common toxins: PCBs, an industrial chemical; and DDT, used in pesticides. These so-called "persistent" pollutants are not easily broken down and remain a health threat years after being banned.
PCBs were banned in the United States in 1979. DDT is banned in the United States, but is still used in some countries to control malaria-carrying mosquitoes, the study authors, from the University of Rochester in New York, said in a university news release.
The researchers analyzed blood samples and immune responses from 516 pairs of mothers and infants in an area of Slovakia heavily contaminated with environmental toxins. Each baby received the tuberculosis vaccine in their first four days of life, and their immune system (antibody) response to the vaccine was assessed six months later.
Harmful chemicals were detected in more than 99 percent of the blood samples. But infants with the highest levels of PCBs and other chemicals had the lowest antibody response to the TB vaccine, the investigators found.
Those with the highest levels of PCBs had 37 percent fewer antibodies against TB than those with the lowest PCB levels. Exposure to DDT also was tied to reduced TB-antibody levels. And infants with exposure to both chemicals had the lowest levels of TB antibodies, the findings showed.
In addition, like many chemicals, PCBs and DDT cross the placenta and are passed from mother to child through breast-feeding, the authors said in the study published online Dec. 9 in the journal Environmental Health Perspectives.
The findings have much broader significance than how exposure to these two chemicals affects TB vaccine responses, according to the researchers.
"There are thousands of pollutants similar to PCBs and DDT with unknown health implications," study leader Todd Jusko, assistant professor in the departments of environmental medicine and public health services, said in the news release. "Our work provides a foundation for how these types of chemicals affect the developing immune system in infants around the world."
It's long been known that TB vaccine response varies between people, but the reasons are unclear. The effect of chemical pollutants on an infant's developing immune system is often overlooked as a possible cause, the researchers said.
But, while the study found an association between exposure to chemicals and reduced response to TB vaccines, it did not prove cause-and-effect.
-- Robert Preidt
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