Part of the receptor for interleukin 6. Binds to IL6 with low affinity, but does not transduce a signal. Signal activation necessitate an association with IL6ST. Activation leads to the regulation of the immune response, acute-phase reactions and hematopoiesis. The interaction with membrane-bound IL6R and IL6ST stimulates 'classic signaling', the restricted expression of the IL6R limits classic IL6 signaling to only a few tissues such as the liver and some cells of the immune system. Whereas the binding of IL6 and soluble IL6R to IL6ST stimulates 'trans-signaling'. Alternatively, 'cluster signaling' occurs when membrane-bound IL6:IL6R complexes on transmitter cells activate IL6ST receptors on neighboring receiver cells. Signaling via the membrane-bound IL6R is mostly regenerative and anti-inflammatory (Probable). Drives naive CD4(+) T cells to the Th17 lineage, through 'cluster signaling' by dendritic cells (PubMed:27893700). Soluble form of IL6 receptor (sIL6R) that acts as an agonist of IL6 activity (PubMed:11113088). The IL6:sIL6R complex (hyper-IL6) binds to IL6ST/gp130 on cell surfaces and induces signaling also on cells that do not express membrane-bound IL6R in a process called IL6 'trans-signaling'. sIL6R is causative for the pro-inflammatory properties of IL6 and an important player in the development of chronic inflammatory diseases (By similarity). In complex with IL6, is required for induction of VEGF production (By similarity). Plays a protective role during liver injury, being required for maintenance of tissue regeneration (PubMed:11113088). 'Trans-signaling' in central nervous system regulates energy and glucose homeostasis (PubMed:28402851). Classic and trans-signaling are both inhibited by tocilizumab, a humanized monoclonal antibody that blocks interleukin IL6R signaling. Component of a hexamer of two molecules each of IL6, IL6R and IL6ST; first binds to IL6 to associate with the signaling subunit IL6ST (PubMed:28265003). Interacts (via N-terminal ectodomain) with SORL1; this interaction may affect IL6-binding to IL6R, hence decrease IL6 'classic-signaling' (PubMed:28265003). Also interacts with SORL1; this interaction leads to soluble IL6R internalization. May form a trimeric complex with the soluble SORL1 ectodomain and circulating IL6 receptor; this interaction might stabilize circulating IL6, hence promote IL6 'trans-signaling'. Expressed by dendritic cells. Detected in the cerebrospinal fluid. Levels in the cerebrospinal fluid are increased in obese mice. The two fibronectin type-III-like domains contained in the C-terminal part form together a cytokine-binding domain. The WSXWS motif appears to be necessary for proper protein folding and thereby efficient intracellular transport and cell-surface receptor binding. A short soluble form is also released from the membrane by proteolysis (PubMed:26876177). The sIL6R is formed by limited proteolysis of membrane-bound receptors, a process referred to as ectodomain shedding (PubMed:26876177). mIL6R is cleaved by the proteases ADAM10 and ADAM17 (PubMed:26876177). Glycosylated. Glycosylation is dispensable for transport, signaling, and cell-surface turnover. Glycosylation at Asn-55 is a protease-regulatory exosite. Glycosylation is required for ADAM17-mediated proteolysis. Belongs to the type I cytokine receptor family. Type 3 subfamily.