Germs on the Skin Play a Protective Role
Although germs are all-around they do not make you sick. They are abundantly present on the largest organ of the body, the skin and within the body as well. They are abundant, diverse and constant, but inflammation is undesirable. A new study produces sufficient evidence to support a radical concept, that germs on the skin are actually beneficial.
The skin is one the major sites of interaction with microbes in the environment. Although immune cells in the skin protect against harmful organisms, until now, it has not been known if the millions of naturally occurring commensal bacteria in the skin, collectively known as the skin microbiota, also have a beneficial role.
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The study that appears online July 26 in Science, had mouse models as their subjects.
The research held by the team from the National Institute of Health observed that the commensals contribute to protective immunity by interacting with the immune cells in the skin.
The investigators colonized germ-free mice with the human skin commensal 'Staphylococcus epidermidis'. The team observed that colonizing the mice with this one species of good bacteria enabled an immune cell in the mouse skin to produce a cell-signaling molecule needed to protect against harmful microbes. The researchers subsequently infected both colonized and non-colonized germ-free mice with a parasite. Mice that were not colonized with the bacteria did not mount an effective immune response to the parasite; mice that were colonized did.
In a separate study they noticed that adding or eliminating beneficial bacteria in the gut did not affect the immune response of the skin. This shows that microbiota present in the skin, gut and lungs play different roles. And in order to maintain good health, the presence of all these several commensal communities is a must.
"The skin bacteria are really critical for controlling immune cells in the skin. They educate immune cells, tell them what to do," explained study author Shruti Naik, a doctoral candidate at the University of Pennsylvania and research fellow at the US National Institute of Allergy and Infectious Diseases. "The pathogen is stealthy, like a burglar. It doesn't want the immune system to detect it. The commensals stimulate the immune system, acting as an alarm saying, 'There is a bug here. You need to fight and ward off this bug.' It's becoming clear that bacteria that live with you are really important for human health. A lot of the focus of research is in understanding the importance of bacteria in the gut."
This study provides new insight into the protective role of skin commensals and demonstrates that skin health relies on the interaction of commensals and immune cells.
What remains unknown is whether skin disorders such as eczema and psoriasis may be caused due to the imbalance of skin commensals.
Justin Sonnenburg, an assistant professor of microbiology and immunology at the Stanford University School of Medicine concluded saying, "What's sure is that humans carry around lots and lots of microbes. Human bodies are home to 10 times as many microbial cells than human cells. The current research is "beautifully done" in showing a strong link between mice microbial skin communities and immune response."