Early Exposure to Germs Shows Lasting Benefits

By HELEN THOMPSON | NATURE | MARCH 27, 2012

Exposure to germs in childhood is thought to help strengthen the immune system and protect children from developing allergies and asthma, but the pathways by which this occurs have been unclear. Now, researchers have identified a mechanism in mice that may explain the role of exposure to microbes in the development of asthma and ulcerative colitis, a common form of inflammatory bowel disease.

Dig in: eating dirt and playing in the mud are thought to confer protection from allergies and asthma.

In a study published online today in Science1, the researchers show that in mice, exposure to microbes in early life can reduce the body’s inventory of invariant natural killer T (iNKT) cells, which help to fight infection but can also turn on the body, causing a range of disorders such as asthma or inflammatory bowel disease.

The study supports the ‘hygiene hypothesis’, which contends that such auto-immune diseases are more common in the developed world where the prevalence of antibiotics and antibacterials reduce children’s exposure to microbes.

“We as a species are not exposed to the same germs that we were exposed to in the past,” says study co-author Dennis Kasper, a microbiologist at Harvard Medical School in Boston, Massachusetts.

The researchers induced two groups of mice — germ-free (GF) mice, which are raised in a sterile environment, and specific-pathogen-free mice raised under normal laboratory conditions — to develop forms of asthma or ulcerative colitis. GF mice had more iNKT cells in their lungs and developed more severe disease symptoms, indicating that exposure to microbes was somehow influencing iNKT cell levels and making the GF mice more susceptible to inflammatory diseases.

The study also found that a lack of exposure in early life could not be compensated for by introducing the GF mice to a broader range of microbes in adulthood.

In search of a mechanism to explain the influence of exposure to microbes, the researchers homed in on CXCL16, a signalling protein associated with inflammation and iNKT cells. Expression of CXCL16 was higher in the colon and lung tissue of GF mice than in normal mice, and blocking that expression reduced the numbers of iNKT cells and the amount of inflammation in those tissues.

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Non-profit sues the FDA for failing to regulate chemicals in Antimicrobials

A nonprofit environmental group has sued the U.S. Food and Drug Administration, claiming the agency failed to regulate toxic chemicals found in “antimicrobial” soap and other personal care products.

Reuters

The National Resources Defense Council alleges that two common ingredients, triclosan and triclocarban, can damage reproductive organs, sperm quality and the production of thyroid and sex hormones.

According to the suit, which also names U.S. Department of Health and Human Services Secretary Kathleen Sebelius as a defendant, recent bio-monitoring results found “residues of triclosan in 75 percent of Americans over the age of 6.”

The lawsuit was filed in U.S. District Court in Manhattan on Tuesday. Representatives of the FDA and the Department of Health and Human Services declined to comment, saying it was a matter of policy not to comment on lawsuits.

Plaintiffs contend that the FDA violated federal law in its delay over establishing safe conditions of use. More than 30 years ago, the agency first proposed to regulate such products for over-the-counter use, but they remain on the market and are unregulated, the group said.

“As a result of the FDA’s lengthy delay, consumers remain exposed to triclosan and triclocarban through a variety of over-the-counter drug products, such as antimicrobial hand soaps, that proliferate on the market,” the lawsuit stated.

The suit seeks an order requiring the FDA to finish its study on the conditions of use by a specific deadline.

No manufacturers or retailers were named as defendants or were cited in the lawsuit.

The FDA said in April it was reviewing the safety of triclosan. It noted there was no evidence it could be harmful to people and did not recommend changing consumer use of products that contain the agent.

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The popularity of antimicrobial products has grown in recent years and the products are increasingly found in homes and offices, where germs can easily be passed from person to person.

The lawsuit cites various recent studies that associate the chemicals with a host of health risks, from lower thyroid hormone levels to the disruption of testosterone production.

In 1978, according to the lawsuit, the FDA proposed to ban from interstate commerce both triclosan and triclocarban either six months or two years after publication of its final study, but no action was taken until 1994, when some ingredients were reclassified.

Healthcare antiseptics containing these chemicals remained on the market and increased in prevalence” since 1994, the lawsuit said.

The National Resources Defense Council said it had met with the FDA to try to hasten the study, to no avail.

Responding to a letter from U.S. Rep. Edward Markey of Massachusetts in February, the FDA said it could not give a specific timeline, but said it was “working diligently” to publish the proposed rule. It also cited a lack of long-term data regarding potential health effects from exposure to the toxins.

The case is National Resources Defense Council v. USDA et al, 10 CIV 5690.