SummaryBackground 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-1b 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 À CD14

Sunlight influences the physiology of the human skin in beneficial as well as harmful ways, as has been shown for UV light. However, little is known about the effects of other wavelengths of solar irradiation. In this study we irradiated human keratinocytes and skin-derived endothelial cells with light-emitting-diode devices of distinct wavelengths to study the effects on cell physiology. We found that light at wavelengths of 632-940 nm has no effect, but irradiation with blue light at 412-426 nm exerts toxic effects at high fluences. Light at 453 nm is nontoxic up to a fluence of 500 J/cm(2). At nontoxic fluences, blue light reduces proliferation dose dependently by up to 50%, which is attributable to differentiation induction as shown by an increase of differentiation markers. Experiments with BSA demonstrate that blue-light irradiation up to 453 nm photolytically generates nitric oxide (NO) from nitrosated proteins, which is known to initiate differentiation in skin cells. Our data provide evidence for a molecular mechanism by which blue light may be effective in treating hyperproliferative skin conditions by reducing proliferation due to the induction of differentiation. We observed a photolytic release of NO from nitrosated proteins, indicating that they are light acceptors and signal transducers up to a wavelength of 453 nm.

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Background: Blue light irradiation reduces the proliferation of keratinocytes and modulates T-cell immune response in vitro and has been shown to reduce the severity of psoriasis vulgaris (Pv) in two clinical trials. Objective: Evaluation of safety and efficacy of long-term UV-free blue light treatment at home for mild Pv. Methods: Forty-seven patients with mild Pv were randomized for receiving high-intensity blue light treatment (HI: 453 nm LED, 200 mW/cm², n = 24) and low-intensity treatment (LI: 453 nm LED, 100 mW/cm², n = 23) of one Pv plaque for 12 weeks. A contralateral control plaque remained untreated. Results: Patient compliance and satisfaction were high. The primary endpoint, change from baseline (CfB) of the Local Psoriasis Severity Index, revealed a significant improvement of the target compared to the control plaques (ΔCfB for the HI group: -0.92 ± 1.10, p = 0.0005; for the LI group: -0.74 ± 1.18, p = 0.0064). Conclusion: UV-free blue light home treatment is safe and improves Pv plaques.