Interleukin-27 receptor alpha is also known as WSX 1, TCCR and IL 27 R alpha. IL-27 R alpha belongs to the typeⅠ,group 2 cytokine receptor family . Mature IL 27 R alpha is a type I transmembrane glycoprotein which is consist of a 484 amino acid aa extracellular region, a 21 aa transmembrane segment and a 99 aa cytoplasmic domain. Human IL-27 R alpha extracellular region show 63% aa sequence identity with those of mouse IL 27 R alpha extracellular domain. It is highly expressed in lymphoid tissues such as spleen, lymph nodes and peripheral blood leukocytes. The function of human IL-27 R alpha is to act as the receptor of human IL-27 and to involve in the regulation of Th1-type immune responses. In addition, IL-27 R alpha is reported to complex with CNTFR alpha and gp130 form a human in receptor on neurons, and to complex with gp130 and IL-6 R to form a receptor for a p28:CLF heterodimeric cytokine on lymphocytes.