TNF and psoriasis: In addition, S100A8 and S100A9 were induced in lesional skin compared to non-lesional and control samples and differences of expression of S100A8 and S100A9 contributed toward the variance in first and second principle components from PCA comparable to genes known to be relevant in the pathogenesis of psoriasis like IL-17A, IL-23A, IL-1A, or TNF.