Nov. 23, 2009 -- Bacteria normally found on the skin's
surface may play a key role in preventing inflammation and disease.
A new study shows that bacteria living on the skin's surface, including
staphylococcal types that typically induce inflammation below the skin,
actually prevent excessive inflammation after injury to the skin.
"It provides a molecular basis to understand the 'hygiene hypothesis' and
has uncovered elements of the wound repair response that were previously
unknown," researcher Richard Gallo, MD, PhD, professor of medicine and
pediatrics at the University of California, San Diego, says in a news release.
"This may help us devise new therapeutic approaches for inflammatory skin
The "hygiene hypothesis" emerged in the late 1980s to explain why allergies like hay fever and eczema
were less common in children from large families who were exposed to more
infectious agents. The theory suggests that a lack of early childhood exposure
to infectious agents and microorganisms changes how the immune system reacts to
In the study, published in Nature Medicine, researchers looked at the
role of bacteria found on the surface of the skin in maintaining healthy
skin using human and mice cell cultures in the lab.
The results showed activation of a Toll-like receptor 3 (TLR3) was necessary
to stimulate normal inflammation after skin injury.
Researchers also found a previously unknown mechanism by which a product of
staphylococci bacteria inhibits skin inflammation. The by-product, known as
staphylococcal lipoteichoic acid (LTA), acts on the main type of cells found in
the outer layer of the skin called keratinocytes via TLR3.
"Keratinocytes require TLR3 to mount a normal inflammatory response to
injury, and this response is kept from becoming too aggressive by
staphylococcal LTA," says Gallo. "To our knowledge, these findings show for the
first time that the skin epithelium requires TLR3 for normal inflammation after
wounding and that the microflora helps to modulate this response."
Researchers say the results emphasize the potential benefit of maintaining
the balance of bacteria found in healthy skin and the potential negative
consequences of altering this balance with the use of topical and systemic