IL23 is a heterodimeric cytokine consisting in two subunits : p40, shared with IL12 and a distinct one p19 (the IL23 subunit). Although IL12 activates naive T cells, the initial description of IL23 was the preferential action on memory T cells to increase IFNg production. In conjunction with IL6 and TGF-beta1, IL23 is necessary to maintain the Th1 lineage. IL23 plays an important role in the inflammatory response against infection, and is implicated in the development of cancerous tumors and auto immune diseases. Over expression of p19 correlates with inflammation in multiple organs and epithelial tissues including skin.