Interleukin-6 (IL-6) (IL-6)

Interleukin-6 (IL-6) is a pleiotropic four-helical cytokine that acts as a central mediator of the immune response, acute-phase reaction, and hematopoiesis. It is produced by a wide variety of cell types, including macrophages, T cells, and fibroblasts, typically in response to infection, trauma, or other immunological stimuli. IL-6 signaling occurs through two primary mechanisms: 'classic signaling' via the membrane-bound IL-6 receptor (IL-6R) and 'trans-signaling' via the soluble receptor (sIL-6R), both of which utilize the gp130 signal-transducing subunit to activate the JAK-STAT pathway. This activation induces the liver to produce acute-phase proteins like C-reactive protein (CRP) and drives the differentiation of B cells into antibody-secreting plasma cells. Dysregulated and chronic overproduction of IL-6 is a major driver of various autoimmune and chronic inflammatory diseases, such as rheumatoid arthritis, Castleman disease, and giant cell arteritis. It also plays a critical role in the systemic inflammatory response observed in cytokine release syndrome (CRS) and severe COVID-19. Therapeutic strategies targeting this pathway include monoclonal antibodies that either neutralize the IL-6 cytokine itself (e.g., siltuximab) or block its receptor (e.g., tocilizumab). While highly effective in dampening systemic inflammation, these interventions are associated with safety risks, including an increased susceptibility to serious bacterial and fungal infections, gastrointestinal complications, and changes in lipid metabolism.

Other names

B-cell stimulatory factor 2 (BSF-2)Hepatocyte stimulating factor (HSF)Hybridoma growth factor (HGF)Interferon beta-2 (IFNB2)Cytotoxic T-cell differentiation factor (CDF)Plasmacytoma growth factor

Monoclonal antibodies bind directly to the circulating Interleukin-6 (IL-6) cytokine, preventing its association with the Interleukin-6 receptor (IL-6R) and the signal-transducing gp130 subunit. This neutralization inhibits the formation of the functional signaling complex, thereby suppressing the JAK-STAT signaling pathway and reducing the production of pro-inflammatory mediators and acute-phase reactants.