Skin Microbes and the Immune Response

NIH | MARCH 11, 2015

Skin is a barrier that serves as one of the body’s first lines of defense against harmful microbes. Specialized immune cells within skin tissue help to fight invading organisms. Yet the skin hosts diverse communities of beneficial bacteria, collectively known as the skin microbiota. These microbes that naturally colonize the skin are referred to as commensals.

Scanning electron microscope image of Staphylococcus epidermidis. Image credit: Janice Carr. Content Providers: CDC/ Segrid McAllister (PD)

The scientists applied Staphylococcus epidermidis, one of the most common species of bacteria on human skin, to the skin of laboratory mice. The bacteria remained on the skin and triggered an immune response in the skin. This led to production of cell-signaling molecules that help combat harmful microbes.

The team found that colonizing the skin of mice with S. epidermidis specifically increased the number of CD8+ T immune cells. These cells produce the immune signaling molecule IL-17A. These responses weren’t associated with inflammation.

Mice colonized with S. epidermidis were protected against later infection with a disease-causing fungus. Depleting CD8+ T cells or neutralizing IL-17A removed this protective effect. Thus, S. epidermidis triggered distinct aspects of the immune system and enhanced immune responses against pathogens without causing inflammation.

IL-17A is known to play a role in various skin disorders, including psoriasis, that typically affect certain skin sites on the body.

This work suggests how variation in microbial communities at different skin sites could contribute to these disorders.

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