IL17A and psoriasis: The pathogenic nature of abnormal Th17 signaling is underscored by the identification of psoriasis associated alleles within IL12B and IL23A [35] (encoding the two subunits of IL-23, a cytokine that drives the polarization of T lymphocytes towards the Th17 lineage), IL23R [33] (encoding the IL-23 receptor), TRAF3IP2 [34] (encoding an adaptor molecule driving NF-κB signal transduction downstream of IL-17) and NFKBIZ [41] (a target of IL-17 signaling in keratinocytes).