IL-6, IL-11, leukemia inhibitory factor (LIF), oncostatin M (OSM), cardiotrophin-1 (CT-1), ciliary neurotrophic factor (CNTF), and cardiotrophin-like cytokine (CLC) belong to the IL-6 family of cytokines. Inclusion in the IL-6 family is based on a helical cytokine structure and receptor subunit makeup. Members of the IL-6 family of cytokines activate the signal transducing receptor protein, glycoprotein 130 (gp130). As they share a common signal transducer, IL-6 family cytokines display both unique and overlapping biologic activities on multiple hematopoietic lineages. In addition, the IL-6 family also includes IL-31. The receptor heterodimer for IL-31 consists of a unique gp130-like receptor chain IL-31RA, and the receptor subunit oncastatin M receptor (OSMR) beta that is shared with OSM. IL-6 family binding to the gp130 alpha subunit induces homodimerization and subsequent activation of Janus kinases (JAK), followed by activation of signal transducers and activators of transcription (STAT1 and STAT3).