The study was approved by the local ethics committee (journal number H-C-2007–0123) and all subjects included gave written informed consent before enrolment. All subjects were sensitized with DPCP in acetone on buttock skin. Petrolatum-backed 11-mm filter disks were soaked in 50 µl

of 0·0625% DPCP in acetone (25 µg/50 µl). Each filter disc was mounted inside a 12-mm aluminium Finn chamber® and taped to the skin (Scanpor®; Epitest Oy, Tuusula, Finland). The disks were left for 48 h. Challenges were carried out on the upper inner arm 3 weeks after sensitization, using four concentrations R788 of DPCP in acetone (0·39, 0·78, 1·56, 3·125 µg/15 µl) and one acetone control on 7-mm filter discs in 8-mm Finn chambers®. The discs were left for 6 h. The challenge sites were all marked with a surgical skin marker for evaluation 48 h later. Sensitization as well as challenge was performed on healthy skin. The elicitation

responses were assessed using a visual score, as suggested by Cooper and co-workers [10]: 1 = no reaction, 2 = mild, macular erythema, 3 = moderate erythema, occasionally with population, 4 = strong erythematous reaction (including vesicular changes) and 5 = extreme or spreading reaction (including bullous or ulcerative reaction). check details The sum increase in clinical score was calculated as the sum of values at the five challenge sites. Increase in dermal thickness, measured using the ultrasound technique, has been shown to correlate well with the strength of an elicitation reaction [11]. In addition to visual scoring, dermal thickness of each elicitation site was determined using a high-frequency ultrasound scanner (Dermascan, Cortex Technology,

Horsens, Denmark). Twelve-mm scanned images were recorded pre- and post-challenge. Five dermal thickness measurements were taken from each pre- and post-challenge scan at fixed distances of 2, 4, 6, 8 and 10 mm along the horizontal length PIK3C2G of the scanned image. A mean percentage increase in dermal thickness was calculated for each elicitation site. Two 4-mm punch biopsies were taken from each patient, one from the challenge area where the highest dose of DPCP (3·125 µg/15 µl) had been applied and one from the area where acetone had been applied. The biopsies were taken 48 h after challenge. Biopsies were taken from 29 individuals; 11 were used for immunohistochemistry and 17 were used for the microarray study. Biopsies taken from 11 individuals, six patients with psoriasis, two of whom had a positive elicitation reaction and five healthy controls, three of whom had a positive elicitation reaction, were prepared for immunohistochemistry. These skin biopsies were embedded in Tissue Tek octreotide (OCT) compound (Sakura Finetek, Zoeterwoude, the Netherlands), frozen instantly in liquid nitrogen and stored at −80°C until use.