Data from: Macrophages contribute to the cyclic activation of adult hair follicle stem cells

Skin epithelial stem cells operate within a complex signaling milieu that
orchestrates their lifetime regenerative properties. The question of
whether and how immune cells impact on these stem cells within their niche
is not well understood. Here we show that skin-resident macrophages
decrease in number because of apoptosis before the onset of epithelial
hair follicle stem cell activation during the murine hair cycle. This
process is linked to distinct gene expression, including Wnt
transcription. Interestingly, by mimicking this event through the
selective induction of macrophage apoptosis in early telogen, we identify
a novel involvement of macrophages in stem cell activation in vivo.
Importantly, the macrophage-specific pharmacological inhibition of Wnt
production delays hair follicle growth. Thus, perifollicular macrophages
contribute to the activation of skin epithelial stem cells as a novel,
additional cue that regulates their regenerative activity. This finding
may have translational implications for skin repair, inflammatory skin
diseases and cancer.