T helper 17 cell/regulatory T‐cell imbalance in hidradenitis suppurativa/acne inversa: the link to hair follicle dissection, obesity, smoking and autoimmune comorbidities

T helper 17 cell/regulatory T‐cell imbalance in hidradenitis suppurativa/acne inversa: the link to hair follicle dissection, obesity, smoking and autoimmune comorbidities

British Journal of Dermatology, June 2018

29573406

B.C. Melnik, S.M. John, W. Chen, G. Plewig

Disintegration of the infundibula of terminal hair follicles (HF) in intertriginous skin areas exhibits the histological hallmark of hidradenitis suppurativa (HS)/acne inversa, featuring a dissecting terminal hair folliculitis. Elevated serum levels of interleukin 17 and local increase in the ratio of proinflammatory Th17 cells and antiinflammatory regulatory T cells (Tregs) have been reported. Perifollicular Tregs play a key role for HF stem cell homeostasis and infundibular integrity. In this review, we evaluate the Th17/Treg ratio in HS, its aggravating conditions and associated comorbidities. Furthermore, we intended to clarify whether drugs with reported beneficial effects in HS readjust the deviated Th17/Treg axis. PubMed-listed, peer-reviewed original research articles characterizing Th17/Treg regulation in hidradentitis suppurativa/acne inversa and associated comorbidities have been selected. This review presents HS as a disease exhibiting an increased Th17/Treg ratio. Perifollicular deficiencies in Treg numbers or function may disturb HF stem cell homeostasis initiating infundibular dissection of terminal HFs and perifollicular inflammation. The Th17/Treg imbalance is aggravated by obesity, smoking as well as decreased Notch signalling. In addition, HS-associated autoimmune diseases exhibit a disturbed Th17/Treg axis resulting in a Th17-dominant state. All drugs that have beneficial effects in the treatment of HS normalise the Th17/Treg ratio. HS immunopathogenesis is closely related to deviations of the Th17/ Treg balance, which may negatively affect Treg-controlled HF stem cell homeostasis and infundibular integrity. Pharmacological intervention should not only attenuate Th17/IL-17 signalling but should improve Treg function to stabilize HF stem cell homeostasis and infundibular integrity This article is protected by copyright. All rights reserved.