Dysregulated cytokine expression in lesional and nonlesional skin in hidradenitis suppurativa

Background There is a dearth of information on the precise pathogenesis of hidradenitis suppurativa (HS), but immune dysregulation is implicated. Objectives To determine the nature of the immune response in HS. Methods Skin biopsies - lesional, perilesional (2 cm away) and uninvolved (10 cm away) -were obtained from patients with HS and healthy controls. The expression of various cytokines was determined by enzyme-linked immunosorbent assay, flow cytometry and real-time polymerase chain reaction. Results The expression of the inflammatory cytokines interleukin (IL)-17, IL-1 beta and tumour necrosis factor-a was enhanced in lesional skin of patients with HS. In addition, IL17A and IL1B mRNA were enhanced in clinically normal perilesional skin. CD4(+) T cells produced IL-17 in HS, while CD11c(+) CD1a(-) CD14(+) cells were sources of IL-1 beta. Activated caspase-1 was detected in HS skin and was associated with enhanced expression of NLRP3 and IL18. Inhibition of caspase-1 decreased IL-1 beta and IL-18 production, suggesting that the caspase-1 pathway participates in IL-1 beta and IL-18 expression in HS. Abnormal cytokine expression was detected in perilesional and uninvolved skin, which may suggest that subclinical inflammation is present in HS skin prior to the formation of an active lesion. Conclusions This study demonstrates that CD4+ T cells produce IL-17 in HS and that the IL-17 pathway may be important in HS pathogenesis. CD11c(+) CD1a(-) CD14(+) cells are a source of IL-1 beta in HS, the production of which was shown to be mediated, in part, via a caspase-1-dependent pathway. These results suggest that IL-17 and the caspase-1-associated cytokines IL-1 beta and IL-18 may play a role in the pathogenesis of HS.