This photomicrograph shows immune cells surrounding hair follicles enriched in beneficial bacteria (red).
In order to determine whether and to what extent commensal skin bacteria cooperate with immune cells to protect the body against harmful infections, researchers cultured S. epidermidis (bacteria normally residing in human skin) on mice bred in a germ-free environment. They then exposed the mice to a parasite, Leishmania major. They observed that the presence of S. epidermidis triggered immune cells in the mouse skin to secrete a cell-signaling molecule that boosts T cells’ response to fight against L. major.
The improvement in T cells’ response due to colonization of the bacterium S. epidermidis was a significant finding in germ-free mice, since before the colonization, the mice had unresponsive T cells. … These findings may lead to the development of new vaccines that work in tandem with exposure to benign local bacteria. Ultimately, it is clear that staying microbe-free does not help our bodies fight against infection; it seems to do just the opposite.
Image courtesy of Lily Koo and Juraj Kabat, Biological Imaging Facility, RTB, NIAID