ICOS and psoriasis: Although levels of inducible co-stimulator (ICOS) (T cell activation marker) and CD1a (expressed by DC and Langerhans cells) increased and PSORS1C2 (terminal differentiation) and CDH12 (cadherin marker) decreased only in AD, the quantification of innate immunity-related marker nitric oxide synthase 2/inducible nitric oxide synthase (NOS2/iNOS) in the tape strips of lesional skin by quantitative PCR was identified to be a potential good biomarker to differentiate AD and psoriasis accurately (19).