Editors' ChoiceHost-Microbe Interactions

Microbes stimulate hair follicles

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Science Signaling  18 Apr 2017:
Vol. 10, Issue 475, eaan4459
DOI: 10.1126/scisignal.aan4459

Commensal microbes induce hair follicles to release a chemokine that recruits regulatory T cells into neonatal skin.

Commensal microbes are important for the proper development and function of the immune system, and regulatory T cells (Tregs) are critical for immune tolerance to commensals. Scharschmidt et al. found that Tregs accumulated in the skin of neonatal mice coincident with the maturation of hair follicles; however, Treg accumulation was reduced in germ-free mice and in mice lacking hair follicles. The presence of microbes stimulated the expression of Ccl20, which encodes a chemokine, in both neonatal mouse skin and human fetal skin explants. Expression of Ccr6, which encodes the receptor for CCL20, was greater in Tregs from mouse neonatal skin than in Tregs from the nearby skin-draining lymph nodes, and a higher proportion of the Tregs in neonatal skin were CCR6+ compared with other immune cells in the tissue. A subset of Tregs isolated from the thymus of neonatal mice was CCR6+, and in vitro experiments showed that CCL20 stimulated the migration of both Tregs isolated from neonatal skin and Tregs derived from neonatal thymocytes. This suggests that the Tregs that were recruited to the skin originated in the thymus. In contrast, the Tregs that mediate tolerance to commensals in the intestine are derived from naïve T cells that differentiate in the mesenteric lymph nodes (see Campbell and Koch). Whereas wild-type Tregs that were transplanted into neonatal mice migrated into both the skin and skin-draining lymph nodes, Ccr6–/– Tregs migrated only into the lymph nodes. Thus, commensal microbes promote the recruitment of Tregs into the skin through a mechanism that at least partially relies on the production of CCL20 by hair follicles.

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