Interleukin-27 heterodimer (IL27) binds a heterodimeric receptor formed by Interleukin-27 subunit alpha (IL27RA) and Interleukin-6 receptor subunit beta (IL6ST, gp130). In the absence of IL27RA IL27 can bind IL6ST with low affinity. Dissociation rate constants for binding of IL27 to the heterodimeric receptor indicate a slow dissociation rate, resulting in very high binding affinity. Blocking both receptor chains completely blocks IL27 induced STAT1 and STAT3 phosphorylation and IL27 induced proliferation (Jia et al. 2016).