Skin biopsies were collected from participants at baseline and after treatment with ustekinumab for 1,2,4 and 16 weeks. The mRNA expression of eight pre-defined IL-23 pathway related genes, namely beta 4 defensin (DEFB4), CXC motif chemokine 8 (CXCL8), Interleukins 17A, 17F, 20, 22, 23A (IL-17, IL-17F, IL-20, IL-22, IL-23A) and cyclic AMP dependent protein kinase (CAMP) was quantitated by qPCR, with the data normalized by the delta-delta Ct method. The expression score for each gene, showing the percentage difference from baseline, was calculated as follows : [(baseline - post baseline)/baseline] x 100. Composite gene expression scores were derived for each individual by summing the expression scores of the individual genes. Positive composite scores denote a reduction from baseline in gene expression.