IL-19 belongs to the IL-10 family of regulatory cytokines, which includes IL-10, IL-19, IL-20, IL-22, IL-24 and IL-26. Members of this family share partial homology in their amino acid sequences, but they are dissimilar in their biological functions. Preliminary data suggests that IL-19 is a proinflammatory cytokine, because it up-regulates IL-6 and TNF-alpha, and induces apoptosis through TNF-alpha. IL-19 signals through the type I IL-20R. Human and murine IL-19 share 71% amino acid sequence identity. Recombinant Human IL-19 is a 35.8 kDa homodimer of two 154 amino acid chains. In solution, IL-19 exists predominantly as a non-disulfide-linked dimer.