IL-23 is an important part of the inflammatory response against infection. It promotes upregulation of the matrix metalloprotease MMP9, increases angiogenesis and reduces CD8+ T-cell infiltration into tumours. IL-23 mediates its effects on both innate and adaptive arms of the immune system that express the IL-23 receptor. Th17 cells represent the most prominent T cell subset that responds to IL-23, although IL-23 has been implicated in inhibiting the development of regulatory T cell development in the intestine. Th17 cells produce IL-17, a proinflammatory cytokine that enhances T cell priming and stimulates the production of other proinflammatory molecules such as IL-1, IL-6, TNF-alpha, NOS-2, and chemokines resulting in inflammation.