IL-27 and the IL-27 receptor complex. Heterodimeric IL-27 is the association between a helical protein, IL-27p28, and a soluble cytokine receptor-like component, EBI3. Through engagement of its cognate receptor, (IL-27R: GP130/WSX-1), IL-27 can activate a heterogeneous Jak/STAT signaling cascade. In order to emphasize structural similarities, IL-27 is depicted with fellow IL-6/IL-12 family cytokines and the conserved WSXWS motif is represented by a dark band within cytokine binding domains. To indicate functional parallels, the relative ability to activate STAT transcription factors is reflected by differences in font size. However, in this figure, the physical size of cytokine/receptor pairings or their components does not have physiological relevance. IL, interleukin; Jak, Janus kinase; STAT, signal transducer and activator of transcription.