Endogenous peroxidase

activity was blocked by incubation for 5 min in peroxidase block, diluted in 0·03% hydrogen peroxide in 95% ethanol. Following three rinses with distilled water, 0·05% Tris-buffered saline (TBS) for 5 min and 1% bovine serum albumin (BSA) in TBS for 10 min, the sections were incubated for 60 min at room temperature with the primary antibodies (mouse anti-human) diluted in 1% BSA/TBS in the following dilutions: anti-CD4 (clone 4B12; 1:20) and anti-CD8 (clone 1A5; 1:20) obtained from Novocastra and anti-forkhead box P3 (FoxP3) antibody (clone 236 A/E7; 1:50), obtained from eBioscience (San Diego, CA, USA). After rinsing with TBS, a secondary antibody (EnVision+ XAV939 kit K4004; Dako, Carpinteria, Y 27632 CA, USA) labelled with horseradish peroxidase was applied for 30 min at room temperature. Enzymatic activity was revealed

by a 5–10-min incubation with 3, 3′-diaminobenzidine (DAB) + substrate-chromogen (EnVision+ kit K4007; Dako), which results in a brown-coloured precipitate at the antigen site. Counterstaining was performed with aqueous Mayer’s haematoxylin (Merck, Darmstadt, Germany). Negative controls were performed with omission of the primary antibody. The sections and antibodies were examined using an LSM 510 microscope (Carl Zeiss MicroImaging, Oberkochen, Germany). Biopsies taken from 17 individuals, seven patients with psoriasis, two of whom had a positive elicitation reaction and 10

healthy controls, five of whom had a positive elicitation reaction, were prepared for the microarray study. Before taking these skin biopsies the skin was frozen using a liquid nitrogen spray to inhibit RNA degradation. The skin biopsies were placed immediately in liquid nitrogen and transferred to a −80°C freezer. For RNA extraction, the frozen skin biopsies were ground in liquid nitrogen, transferred to lysis/binding buffer (Applied Biosystems, Rotterdam, the Netherlands) and homogenized with a rotor stator (Polytron PT3000; Kinematica AG, Buch TCL & Holm A/S, Herlev, Denmark). Total RNA was then extracted using the mirVanaTM isolation kit (Applied Biosystems) following the manufacturer’s specifications. RNA concentration was determined using a NanoDrop spectrophotometer (NanoDrop Technologies, Wilmington, DE, USA) and the RNA quality was assessed using an Agilent RNA 6000 nano kit on a 2100 Bioanalyzer (Agilent Technologies, Santa Clara, CA, USA). The RNA was stored at −80°C. The microarrays used for this study were Human Gene 1·0 ST arrays (Affymetrix Inc., Santa Clara, CA, USA) containing probe sets of approximately 26 000 genes. Generation of cDNA, biotin-labelled cRNA and GeneChip hybridization was performed by the RH Microarry Centre at Rigshospitalet (Copenhagen, Denmark).