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Abstract
IL-10 is an important mediator of immunoregulation, which exerts potent immunosuppressive activity by downregulating monocytic cell and T cell activation. Recently, five novel human cytokines structurally related to IL-10 and designated IL-19, -20, -22, -24 and -26 have been identified through genomic methods. All are secreted α-helical proteins whose amino acid sequences show 20 – 30% identity to that of IL-10. Furthermore, all the known cell surface receptors utilised by these cytokines are heterodimers of transmembrane subunits that belong to the Class II cytokine receptor family and signal predominantly through Janus kinases (JAKs)–signal transducer and activator of transcription (STAT) pathways. Preliminary characterisation of the biological activities of these new IL-10 family members has demonstrated that they all lack the immunosuppressive activity of IL-10 but perform diverse roles in mediating inflammatory responses in a variety of tissues. In particular, IL-19, 20 and -22 may be involved in skin inflammation, such as psoriasis. Moreover, adenovirus expression of IL-24 has antitumour activity and is being evaluated for cancer gene therapy. The potential of these cytokines and their receptors as therapeutic targets for inflammatory or malignant diseases has prompted considerable interest in both academia and the biopharmaceutical industry. This article provides an updated overview of the molecular and functional properties of these molecules and discusses the associated patent literature.