Beneficial bacteria on the skin of lab mice work with
the animals' immune systems to defend against disease-causing microbes and
accelerate wound healing, according to new research. Researchers say untangling
similar mechanisms in humans may improve approaches to managing skin wounds and
treating other damaged tissues.
Like humans and other mammals, mice are inhabited by
large, diverse microbial populations collectively called the microbiome. While
the microbiome is believed to have many beneficial functions across several
organ systems, little is known about how the immune system responds to these
harmless bacteria.
To investigate, NIAID scientists led by Yasmine
Belkaid, Ph.D., chief of the Mucosal Immunology Section of NIAID's Laboratory
of Parasitic Diseases, observed the reaction of mouse immune cells to Staphylococcus
epidermidis, a bacterium regularly found on human skin that does not normally
cause disease. To their surprise, immune cells recognized S. epidermidis using
evolutionarily ancient molecules called non-classical MHC molecules, which led
to the production of unusual T cells with genes associated with tissue healing
and antimicrobial defense. In contrast, immune cells recognize disease-causing
bacteria with classical MHC molecules, which lead to the production of T cells
that stoke inflammation.
Researchers then took skin biopsies from two groups of
mice -- one group that had been colonized by S. epidermidis and another that
had not. Over five days, the group that had been exposed to the beneficial
bacteria experienced more tissue repair at the wound site and less evidence of
inflammation. Dr. Belkaid's team plans to next probe whether non-classical MHC
molecules recognize friendly microbes on the skin of other mammals, including
humans, and similarly benefit tissue repair. Eventually, mimicking the
processes initiated by the microbiome may allow clinicians to accelerate wound
healing and prevent dangerous infections, the researchers note.
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