Figure 1.

A schematic detailing the psychopathology of alopecia areata. Autoimmune and apoptotic pathways are detailed; however, only approximate flows are shown, and detailed signaling processes are excluded for conciseness. The autoimmune pathway, the major pathway in alopecia areata development, is indicated by a thick line; ligands associated with the autoimmune pathway are shown in blue. The reason for which neurogenic inflammation stimulates hair follicles to enter the catagen phase early is unclear; therefore, this is indicated by a dotted line. The apoptotic pathway, the minor pathway in alopecia areata development, is indicated by a thin line; ligands associated with the apoptotic pathway are shown in green. The apoptotic pathway interacts with the autoimmune pathway by downregulating the expression of tropomyosin receptor kinase A and upregulating the expression of the p75 neurotrophin receptor, which also contributes to the early entry into the catagen phase; therefore, this is indicated by a line with an intermediate thickness. Abbreviations: CRH, corticotropin-releasing hormone; NGF, nerve growth factor; TNF-α, tumor necrosis factor-α; TrkA, tropomyosin receptor kinase A; p75NTR, p75 neurotrophin receptor; CD8+ T cell, cluster of differentiation 8+ T cell; IL-15, interleukin 15; IFN-γ, interferon-gamma; and MHC, major histocompatibility complex.