The interleukin-27 receptor is a type I cytokine receptor for interleukin-27. It is a heterodimer composed of the interleukin 27 receptor, alpha subunit, and glycoprotein 130. WSX-1/IL-27R, a class I cytokine receptor that is homologous to the β2 chain of the IL-12R in both sequence and structure, is highly expressed by resting/naive CD4+ T cells and CD8+ T cells. WSX-1/IL-27R belongs to the IL-6/IL-12 family of cytokines and induced proliferation of naive CD4(+) T cells and the generation of a Th1-type adaptive immune response. WSX-1/IL-27R functions as a receptor for IL27. IL-27 not only contributes to the development of an adaptive immune response through its action on CD4(+) T cells, it also directly acts on cells of the innate immune system. WSX-1/IL-27R requires IL6ST/gp130 to mediate signal transduction in response to IL27. This signaling system acts through STAT3 and STAT1. It is involved in the regulation of Th1-type immune responses. IL-27R also appears to be involved in innate defense mechanisms. IL27RA is essential for transcriptional activation of STAT1 and for augmenting the induction of T-bet expression during initiation of Th1 cell differentiation.