Expression of Programmed Cell Death 1 Inversely Correlated With the Density of CD8+ T Cells Infiltrating Hair Follicles in Alopecia Areata

The study examined the relationship between the expression of programmed cell death 1 (PD-1), an inhibitory receptor that suppresses T cell activation, and the infiltration of CD8+T cells in hair follicles (HF) in alopecia areata (AA), an autoimmune disease. The research involved 45 biopsied skin samples from individuals with AA, with the expression of PD-1, CD3, and CD8 evaluated in 19 samples. The results showed that as the number of inflamed HF and the density of infiltrating CD3+T cells increased, the anagen/telogen ratio decreased. Furthermore, the expression of PD-1 was found to be inversely correlated with the density of infiltrating CD8+T cells, suggesting that the PD-1/PD-L1 axis negatively controls the infiltration of CD8+T cells in HF. This implies that enhancing the PD-1/PD-L1 axis could potentially improve AA by inhibiting the infiltration of CD8+T cells to HF.