The skin is the largest organ of the human body and the first line of defense against harmful microorganisms in the environment. However, it is also home to trillions of microbes that are beneficial to the host individual. In a study published in Nature, scientists found that specific bacteria on mammalian skin influence the host immune response.
To better understand this relationship, researchers chose Staphylococcus epidermidis, a bacterium commonly found on human skin, to see how the bacterium shaped the immune response. Using mice, the researchers found that the presence of S. epidermidis on mice skin caused an increase in CD8 β+ T cells, cells that are involved in immune response. The application of other common skin bacteria to mice resulted in the increase of different T cell populations. The scientists next investigated how the skin cells detected the presence of S. epidermidis. The results suggested that a specific type of dendritic cell – located not on the exterior epidermal layer of skin cell, but within the dermal, second layer of the skin – is the cause of the unique CD8 β+ T cell response.
While mechanisms are still unclear, it is possible that S. epidermidis produce specific proteins that can trigger an immune response within the human skin when exposed to skin pathogens. What is clear from this study is that different bacteria living on the skin can elicit different immune responses. This suggests a commensal or possibly mutualistic relationship between skin cells and certain bacteria. Further investigation and knowledge of this relationship could lead to better understanding of the immune system and how the human microbiome participates in immunity as well as how this can be translated into therapy.