Childhood Exposure to Germs Can Bolster Immune System
A new study suggests that getting a little dirty might be good for your health. The research found that adult mice raised in a germ-free lab environment were more likely than normal lab mice to develop allergies, asthma and other serious autoimmune disorders, in which normally defensive immune system cells turn against the body’s tissues and organs.
There are more than 80 autoimmune disorders, including common allergies such as hay fever; rheumatoid arthritis, which attacks the joints; Crohn’s disease, an inflammatory bowel condition; and juvenile diabetes.
Richard Blumberg, a professor at Harvard Medical School and chief of gastroenterology at Brigham and Women’s Hospital in Massachusetts, says medical researchers in 1989 sought to explain these varied autoimmune disorders with what they called the “hygiene hypothesis."
“The hypothesis has stated or suggested that early-life exposure to microbes is a very important determinant of later life sensitivity to allergic and so-called autoimmune diseases, such as hay fever, asthma, inflammatory bowel disease and others," said Blumberg.
The hygiene hypothesis proposed that all the washing and scrubbing people were doing with the increasingly popular anti-bacterial soaps and lotions could be making them sick by altering their immune systems. But this theory had not been tested, until now.
Blumberg and colleagues have found the first biological evidence that childhood exposure to germs keeps the adult immune system in check, preventing the development of some autoimmune diseases. They compared a group of mice raised in a typical environment filled with bacteria, to a group of mice raised in a sterile environment.
The researchers discovered that inflammation in the lungs and colon of the adult germ-free mice was being caused by over-active killer T cells. These cells normally fight infection, but in these mice they were targeting healthy tissue - an autoimmune condition seen in asthma and ulcerative colitis.
But Blumberg says the normal mice whose immune systems had been “educated” by exposure to a microbe-rich enviornment did not have the same inflammatory response.
“What was really most remarkable to us was the fact that once the education event provided by the microbes occurred in early life, it was durable and lasted throughout the life of the animal," he said. "And if that educational event provided by microbes was not given, it was impossible to educate the animal later in life.”
Blumberg's team concluded that there is a critical window of opportunity early in life for microbial exposures to provide lifelong protection against the development of autoimmune disorders.
The incidence of these disorders is rising worldwide, but mostly in wealthier, industrialized countries. Blumberg suggests this might be due to the way routine childhood illnesses are treated there.
“I think one obvious question, for example, that’s raised by these studies is the early life use of antibiotics and whether we need to be more careful in their prescribing," said Blumberg.
Rob Dunn thinks he knows the answer to that question. He's a professor of ecology and evolutionary biology at North Carolina State University in Raleigh. He points out that not too many years ago, it was common for children in the United States to be infected with harmless intestinal parasites, such as hookworms and whipworms. He says these parasitic infections played a positive role in preventing autoimmune disease.
Dunn notes that medical researchers are only now beginning to understand a possible connection between beneficial parasites and illness in humans. He says the latest findings do NOT mean, however, that people should stop washing.
“Wash your hands but don’t do it with anti-microbial soap," said Dunn. "Let your kids play in a reasonable amount of dirt and get outside and get exposed to a diversity of things!”
The study by Richard Blumberg and colleagues, demonstrating how early exposure to germs strengthens the body's immune system, is published in the journal Science.
Source: Voice of America
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