Characterization of infiltrating T cells in human scalp explants from alopecia areata to SCID nude mice: possible role of the disappearance of CD8+ T lymphocytes in the process of hair regrowth.

T cells may play a role in the pathogenesis of alopecia areata (AA). We attempted to elucidate the linkage between infiltrating T cells and hair regrowth processes by grafting scalp skin from the affected region of patients with AA onto severe combined immune deficiency (SCID) nude mice. When the AA scalp was grafted into the mice, the grafts were accepted, and normal hair regrowth was observed. Before grafting, CD4+ and CD8+ T cells had infiltrated into the peribulb area. After grafting, the telogen hair shifted to anagen hair, and the CD4+ and CD8+ T cell infiltrates in the bulb area decreased in all cases. CD8+ T cells had almost disappeared from all portions of the follicles. It has been suggested that CD8+ T cells play a crucial role in the pathogenesis of AA. The absence of CD8+ T lymphocytes that responded to follicular autoantigens may induce hair regrowth in the grafted skin. In addition, the CD4+ human T cells that had infiltrated or still remained in the upper-middle portions including the bulge area accompanied the HLA-DR expression after grafting. Infiltrating or surviving T cell phenotypes and locations changed during the hair cycle in the grafts. These results indicate that the location of infiltrated T cells and their phenotypes may participate not only in hair loss but also in regrowth of hair in AA.