To prevent degradation by intracellular RNases, tissues were embedded soon after excision in RNA stabilizing reagent RNAlater provided from QIAGEN worldwide companies according to the manufacturer's instructions to be stored at -70°C before sample processing. Frozen tissues were not allowed to thaw during handling to be ready for Interleukin-18 expression and the response to treatment in patients with psoriasis quantitative PCR determination of IL-18. Each biopsy was weighed before processing. Biopsies weighed up to 20 mg. Efficient disruption and homogenization of the starting material was performed using a rotor-stator homogenizer.