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Epithelialized Tunnels: Source of Inflammation in HS

A study published in the Journal of Allergy and Clinical Immunology found that hidradenitis suppurativa (HS) tunnels are a source of inflammation, often causing significant burden in patients with the disease.

In order to determine whether HS tunnels are immunologically active in HS activity, the study used skin biopsy specimens obtained by using ultrasound guidance in untreated patients with HS and compared these samples to those of patients enrolled in an open-label study of brodalumab for moderate to severe HS.

Upon analysis, the immunohistochemistry of HS biopsy specimens demonstrated that the epithelialized HS tunnels show a similarity to the psoriasiform epidermal hyperplasia morphology of the overlying epidermis. This recapitulation displays molecular inflammation (ie, S100A7/psoriasin positivity) and features of epidermal skin, including loricrin, filaggrin, lipocalin-2, and Melan-A positive cells. According to the results, tunnels were associated with increased infiltration of T cells, dendritic cells, and neutrophils, as well as formation of neutrophil extracellular traps and increased expression of psoriasiform proinflammatory cytokines.

Further, the authors noted that unsupervised hierarchical clustering demonstrated a separation of HS samples based on the presence or absence of tunnels, finding “tunnels isolated by microdissection had higher levels of epithelium-derived inflammatory cytokines compared with the overlying epidermis and healthy controls.” Brodalumab decreased the size and draining of the tunnels.

The results of this study suggest that tunnels are a major source of inflammation in HS, and more research into effective therapies addressing this burdensome disease and its signs are needed. –Jessica Garlewicz


Navrazhina K, Frew JW, Gilleaudeau P, Sullivan-Whalen M, Garcet S, Krueger JG. Epithelialized tunnels are a source of inflammation in hidradenitis suppurativa. J Allergy Clin Immunol. Published online February 3, 2021. doi:10.1016/j.jaci.2020.12.651

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