Squeaky clean mice show that skin bacteria help shape immunity

Los Angeles Times

The psychedelic image above is a super-close-up view of the skin -- and the brightly colored blobs are immune cells. What’s it about? Read on.

Evidence is mounting that the bacteria that live on our bodies affect our health, for good or ill. It’s a hot area of research, much of it centered on the gut -- and no wonder, for this is the spot where the richest bacterial communities are found. The bugs that dwell there seem to help our immune systems develop along the right lines, among other things. (They can also contribute to disease.)

Compared with the gut, the skin is a sparse Sargasso Sea when it comes to microbial numbers, though it still houses plenty of bacteria. These populations are less studied than the gut.


And as the colorful image above shows, there are plenty of immune cells on the skin, helping to protect our hides from pathogens.

Now a new paper shows that bacteria residing on the skin help shape the skin’s immunity.

The authors of the paper, published online in Science Express, found that mice raised in a germ-free environment (with no bugs on their skin or in their guts or anywhere) had abnormalities in how T cells of the immune system behave on skin.

When the bacterium Staphylococcus epidermidis, which normally lives on skin, is added back to the squeaky-clean creatures’ hides, the mice’s immune responses are restored to normal.

Furthermore, when the germ-free mice are infected with a single-celled parasite called Leishmania major, the T cells didn’t produce chemicals important in mounting a response against the parasite. The skin also developed less inflammation and smaller lesions, which may sound like a good thing -- but then again, the inflammatory response is important for fighting infections.

Adding back the staph bacterium helped protect against the parasite, the scientists found.

Inflammation, of course, is part of bothersome conditions of the skin such as psoriasis. The scientists suggest that a downside of these normal skin residents is that they can help promote these conditions.