A commensally regulated immune rheostat fine-tunes skin barrier fitness.

Langerhans cells in mouse epidermis produce prostaglandin E2 that restrains stem cell proliferation and maintains barrier integrity during homeostasis.

• Why it matters: Skin must coordinate stem cell renewal with barrier maintenance under environmental and microbial fluctuations, but the microbial-to-stem-cell control logic is unclear.
• What they did: In mice, the study mapped a microbial-immune-epithelial feedback circuit where LC prostaglandin E2 regulates stem cell proliferation and differentiation, and tested effects of pathway disruption.
• The result: Disrupting this pathway overactivates stem cells, impairs terminal differentiation, and weakens barrier function, implying commensal sensing can fine-tune adaptive epidermal homeostasis.

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