Alopecia Areata in C3H/HeJ Mice Involves Leukocyte-Mediated Root Sheath Disruption in Advance of Overt Hair Loss

In this study, alopecia areata (AA) was induced in C3H/HeJ mice by grafting AA-affected skin, with a delay of 8-12 weeks before visible hair loss. Inflammation initially appeared around anagen-stage hair follicles near the graft site and later spread to distant sites, focusing on these follicles by 10-12 weeks. The inflammation was primarily composed of CD4+ and CD8+ cells, with CD8+ cells penetrating the follicles by 12 weeks. Electron microscopy revealed significant lymphocyte and macrophage infiltration in the root sheaths, leading to hair follicle dystrophy. The findings indicated that follicular inflammation and root sheath disruption occurred well before overt hair loss, with the severity of inflammation reaching a threshold before hair loss became visible.