Alopecia areata is characterized by expansion of circulating Th2/Tc2/Th22, within the skin‐homing and systemic T‐cell populations

Background Characterizing blood profile of alopecia areata (AA) is important not only for treatment advancements, but also for possibly identifying peripheral biomarkers that will eliminate the need for scalp biopsies. We aimed to compare frequencies of skin homing (CLA+) vs systemic (CLA−) “polar” CD4+ and CD8+ and activated T‐cell subsets in AA vs atopic dermatitis (AD) and control blood. Methods Flow cytometry was used to measure IFN‐γ, IL‐13, IL‐9, IL‐17, and IL‐22 cytokines in CD4+ and CD8+ T cells. Inducible co‐stimulator molecule (ICOS) and HLA‐DR were used to define mid‐ and long‐term T‐cell activation. We compared peripheral blood from 32 moderate‐to‐severe AA adults with 43 moderate‐to‐severe AD patients and 30 age‐matched controls. Results AA patients had increased CLA+/CLA− Th2 (P