Serum thymus and activation‐regulated chemokine as disease activity and response biomarker in alopecia areata

Serum thymus and activation‐regulated chemokine/ CCL 17 (s TARC ) is known as a good indicator for atopic dermatitis severity. Herein, we investigate whether s TARC correlates with severity and therapeutic response for alopecia areata ( AA ) in our 121 patients. The s TARC mean of AA totalis and universalis was significantly higher than mild AA . Next, we compared s TARC of diffuse AA ( n  = 14) and severity‐controlled patchy AA ( n  = 32) and found that s TARC in diffuse AA (564.2 ± 400.0 pg/mL) was significantly higher than that of the patchy type (344.0 ± 239.8 pg/mL), suggesting a potential role of TARC in active progression of diffuse AA . Ten patients with diffuse AA were treated with i.v. corticosteroid pulse therapy. Then, we tested whether s TARC can predict prognosis after the pulse therapy and found that baseline s TARC in the poor responders (1025.5 ± 484.8 pg/mL) was significantly higher than that in the good responders (complete remission at 24 months after the pulse therapy, 347.8 ± 135.7 pg/mL), indicating s TARC as a response biomarker in the corticosteroid pulse therapy for diffuse AA . Finally, to investigate TARC production in the affected hair follicles, we performed immunohistochemical double staining of TARC and CD 68 using scalp skin specimens of diffuse AA with high titers of s TARC . The results showed their co‐localization in the infiltrating cells around the AA hair follicles, suggesting that TARC is mainly produced from CD 68 + histiocytes. In conclusion, s TARC is a disease activity and response biomarker in AA , providing new insight beyond the T ‐helper 1/2 paradigm to solve the immunological pathogenesis of AA .