[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Immunology](https://durgical.com/en/immunology/) › [Cytokines and molecules](https://durgical.com/en/immunology/#a-molecules) › Interleukin-6 [Immunology](https://durgical.com/en/immunology/) · [Cytokines and molecules](https://durgical.com/en/immunology/#a-molecules) # Interleukin-6 - Molecule IL-6 tells the liver to make CRP and other acute-phase proteins. Blocking its receptor is a treatment for rheumatoid arthritis and cytokine storms. Updated 2026-11-01 ## Key points - Main inducer of CRP, fibrinogen, serum amyloid A and hepcidin in the liver. - Hepcidin traps iron: IL-6 explains the anaemia of inflammation. - Receptor: IL-6R + gp130 → JAK/STAT3. - B cells → plasma cells (more immunoglobulins); with TGF-β it pushes naive T cells to Th17 instead of Treg. - Tocilizumab and sarilumab block the IL-6 receptor; siltuximab blocks IL-6 itself (Castleman disease). - On tocilizumab CRP may stay low during infection: fever and CRP can be misleading. ## What it is Interleukin-6 is made mainly by macrophages and other myeloid cells, and also by T cells, fibroblasts and fat tissue. It acts through the IL-6 receptor plus the signalling chain gp130 (classic signalling on cells with membrane IL-6R, trans-signalling through soluble IL-6R on almost any cell). It is the main trigger of the hepatic acute-phase response and links innate inflammation with B-cell and Th17 responses. ## Function - Acute-phase response and fever, together with IL-1 and TNF-α. - Recruitment of neutrophils and monocytes. - Differentiation of B cells into antibody-secreting plasma cells. - Decides between Th17 (IL-6 present) and regulatory T cells (TGF-β alone). ## Clinical notes - Rheumatoid arthritis, giant cell arteritis, juvenile idiopathic arthritis and systemic sclerosis lung disease: tocilizumab. - Cytokine release syndrome (after CAR-T cells) and severe COVID-19 needing oxygen: tocilizumab. - Before treatment: screening for latent tuberculosis and hepatitis B, because infections may become severe. - Known effects of IL-6 receptor blockade: neutropenia, raised lipids, liver enzyme changes and, rarely, bowel perforation (especially with diverticulitis). ## In the lab - CRP rises within hours of inflammation because of IL-6; it falls quickly once IL-6 signalling stops. - Low CRP under tocilizumab does not rule out infection. ## Memory aid IL-6 is the liver's messenger: it sends the order and the liver replies with CRP. ## Test yourself Think of the answer, then tap the question to see it. ## Which cytokine is the main driver of CRP synthesis? IL-6, acting on hepatocytes through IL-6R/gp130 and STAT3. ## How does IL-6 cause the anaemia of inflammation? It induces hepcidin, which blocks iron release from macrophages and gut cells, so less iron reaches the marrow. ## Why can infection be hidden in a patient on tocilizumab? Blocking the IL-6 receptor suppresses CRP and fever, so the usual signs of infection may be absent. [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/immunology/interleukin-6/) ## Related - [Cytokines: the table to know](https://durgical.com/en/immunology/cytokines-the-table-to-know/) - [Interleukin-1](https://durgical.com/en/immunology/interleukin-1/) - [TNF-α](https://durgical.com/en/immunology/tnf/) - [Interleukin-17](https://durgical.com/en/immunology/interleukin-17/) - [IL-10 and TGF-β (the brakes)](https://durgical.com/en/immunology/il-10-and-tgf/) - [Acute-phase response and fever (CRP, ESR, procalcitonin)](https://durgical.com/en/immunology/acute-phase-response-and-fever/) - [Th1, Th2, Th17, Tfh and Treg](https://durgical.com/en/immunology/th1-th2-th17-tfh-and-treg/) - [Monoclonal antibodies and biologics: naming and targets](https://durgical.com/en/immunology/monoclonal-antibodies-and-biologics-naming-and-targets/) ## Related conditions - [Rheumatoid arthritis](https://durgical.com/en/conditions/rheumatoid-arthritis/) ## In Pharmacology - [Tocilizumab](https://durgical.com/en/pharmacology/tocilizumab/) [← All of immunology](https://durgical.com/en/immunology/) Educational content on the immune system; not a treatment or individual vaccination guide and no substitute for a health professional's advice. No doses are given. Sources: [Update on tocilizumab in rheumatoid arthritis: a narrative review](https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2025.1470488/full) (Frontiers in Immunology, 2025); [Tocilizumab Injection: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a611004.html) (MedlinePlus (U.S. National Library of Medicine), 2025); [Pro-Inflammatory and Anti-Inflammatory Interleukins in Infectious Diseases: A Comprehensive Review](https://pmc.ncbi.nlm.nih.gov/articles/PMC10818686/) (Tropical Medicine and Infectious Disease (PubMed Central), 2024); [Regulation of Treg cells by cytokine signaling and co-stimulatory molecules](https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2024.1387975/full) (Frontiers in Immunology, 2024). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/immunology/interleukin-6/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/immunology/interleukin-6/