The crosstalk of monocyte-neutrophil in hair follicles regulates neutrophil transepidermal migration in contact dermatitis

This study investigates the mechanisms of neutrophil transepidermal migration (NTEM) in contact dermatitis using a murine model. Researchers used trichromatic-fluorescence-labeled chimeric mice to visualize NTEM and the interaction between neutrophils and monocytes. They found that neutrophils preferentially migrate through hair follicles, where they interact with dermal monocytes. The study identifies MMP-9 as essential for NTEM, with dermal monocytes being a crucial source of TNF-α and CXCL2, which promote MMP-9 expression in neutrophils. Depletion of dermal monocytes significantly reduces MMP-9 expression and inhibits NTEM, highlighting hair follicles as key sites for monocyte-modulated NTEM in inflammatory skin disorders.