Microbes do not leave for tomorrow what they can do today. In a new study in mice, U.S. researchers have found that, during the first years of life, microorganisms carefully train the immune system.
“This work shows the critical importance of exposure to germs during early life stages to develop the immune system,” said SINC Dennis L. Kasper, a researcher at Harvard Medical School (Boston, USA) and one of the authors.
The research, published in the journal Science, reinforces the ‘hygiene hypothesis’, a term that relates the increase in inflammatory diseases such as asthma with reduced exposure to microbes during early life. The experiments tested the immune system of two groups of mice. A population was free of bacteria and the other lived in normal environments with microbes.
Animals in the first days of life had not come into contact with microbes were more susceptible to the induction of colitis (colon inflammation) and allergic asthma. Tests showed that germ-free mice had more of natural killer cells (NKT) in the colon and lungs because the bacteria had not contributed to the regulation of the amount and function of these cells the immune system.
In Kasper’s words, “the NKT cell hyperactivity” exaggerated CXCL16 receptor expression, which has a close relationship with inflammation hence the increased sensitivity asthma. Furthermore, contact of adult mice and microbes prevented colitis and asthma to keep the level of NKT cells. However, adult exposure to these microorganisms could not reverse the disease or inflammation.
Although no direct relationship has been demonstrated, Kasper insists that human epidemiological studies are suggesting that inadequate exposure to microbes during the first years of life “are decisive for sensitivity to allergies and other autoimmune diseases in life adult.”