Interleukin-6 (IL-6) und IL-6-Autoantikörper: the pathway in the body

Interleukin-6 (IL-6) und IL-6-Autoantikörper is part of the pathway “CRP”. This page shows the whole pathway; the station of Interleukin-6 (IL-6) und IL-6-Autoantikörper is highlighted.

Where this laboratory value sits: Interleukin-6 — Immune cell messenger. When tissue is irritated, macrophages and other cells release the messenger interleukin-6. It travels with the blood to the liver. The more of it arrives, the more CRP the liver makes. Source 1

In brief

CRP (C-reactive protein) is a ring-shaped protein that the liver forms in response to the signal interleukin-6. With calcium it binds to phosphocholine on damaged cells and bacteria and marks them for the complement system and phagocytes. Its amount follows the IL-6 signal.

The pathway step by step

Each station states what the compound does there. Three signs: ↑ supplies — builds up or makes available · ↓ depletes — inhibits, consumes or withholds · ↕ both, depending on amount. Behind it stands what the statement rests on: established physiology, observed in studies, or contested. The signs do not grade; they name the direction.

1. Interleukin-6 → IL-6 receptor · gp130 Interleukin-6 binds to its receptor. Together with the protein gp130, this forms a signalling complex in the cell membrane. If the receptor is blocked, the signal does not get through. Source 1↑ supplies Only the complex of IL-6, receptor and gp130 passes the signal into the cell. The receptor also exists in soluble form in the blood; with it, IL-6 also reaches cells that carry only gp130. established physiology Source 1
   ⚖ When the balance tips

   too much — If more receptors are occupied by IL-6, more gp130 complexes form and the signal in the liver cell grows stronger; the cell slows it via the protein SOCS3, which it then makes itself.

   too little — If the receptor is barely occupied by IL-6 or blocked by tocilizumab, the signal does not reach the inside of the cell, and the liver makes less CRP.

   established physiology · Source 1, 5

2. IL-6 receptor → STAT3 in the nucleus JAK kinases · ATP JAK kinases sitting at the receptor attach phosphate to STAT3. The modified STAT3 molecules pair up and move into the cell nucleus. There STAT3 switches on the reading of genes such as the CRP gene. Source 1, 2↑ supplies Phosphorylated STAT3 is the switch in the nucleus: it starts the reading of acute-phase genes such as the CRP gene. At the same time it has SOCS3 made, which switches the pathway off again. established physiology Source 1, 2
   ⚖ When the balance tips

   too much — If STAT3 stays activated for long, acute-phase genes continue to be read; normally the SOCS3 made by STAT3 itself ends the signal after a while.

   too little — If little STAT3 is activated, hardly any signal reaches the nucleus, and the CRP gene is read only rarely.

   established physiology · Source 1, 2

3. STAT3 in the nucleus → CRP gene is read · C/EBPβ STAT3, together with the factor C/EBPβ, binds to the start of the CRP gene. RNA polymerase transcribes it. Interleukin-1 can further amplify this reading. Source 2↑ supplies At the CRP gene, STAT3 and C/EBP factors act together; interleukin-1 can amplify the effect of IL-6 via the factor NF-κB. The strength of these signals determines how often the gene is read. established physiology Source 2
   ⚖ When the balance tips

   too much — If IL-6 and interleukin-1 arrive together, the gene is read more often than with one signal alone, and CRP production rises sharply within hours.

   too little — If hardly any signals arrive, the CRP gene is read only rarely, and the liver releases little CRP into the blood.

   established physiology · Source 2, 3

4. CRP gene is read → CRP pentamer RNA polymerase II The liver cell assembles five identical protein subunits into a flat ring and releases it into the blood. hsCRP is the name for a particularly sensitive measurement of this protein. Its amount in the blood follows the rate of production. Source 2, 3↕ both, depending on amount As a ring, CRP binds phosphocholine and directs complement and phagocytes there. If the ring breaks apart into single subunits (mCRP) on damaged membranes, these amplify the inflammatory response in cell and animal studies. observed in studies Source 3, 2
   ⚖ When the balance tips

   too much — If a lot of CRP is made, its amount in the blood rises, because breakdown continues at a steady rate; the rate of production alone determines how much CRP circulates.

   too little — If little CRP is made, little remains in the blood, because steady breakdown keeps removing the protein present; the amount falls quickly once production eases.

   established physiology · Source 3

5. Binding phosphocholine → C1q The bound face of the ring holds on to C1q, the first component of the classical complement pathway. This starts the complement pathway; the regulator factor H slows its late steps. Source 2, 3↑ supplies When bound CRP holds C1q, the classical complement pathway starts. CRP also binds the regulator factor H, so the chain usually ends at C3b and rarely proceeds to the membrane-destroying complex. established physiology Source 2, 3
   ⚖ When the balance tips

   too much — If a lot of C1q is bound to CRP, more complement chains start and more C3b is attached to surfaces; factor H limits the late steps.

   too little — If little CRP is bound, the classical pathway starts less often at these sites; C1q can, however, also bind to antibodies and start the pathway that way.

   established physiology · Source 2, 3

6. Binding phosphocholine → Fcγ receptors The same face fits the Fcγ receptors of phagocytes. Through them, the cells recognise what CRP has marked. This triggers engulfment of the particle. Source 4↑ supplies Through the Fcγ receptors, CRP triggers phagocytes to engulf the marked particle and changes which messengers the cell releases. observed in studies Source 4
   ⚖ When the balance tips

   too much — If many CRP rings bind to Fcγ receptors, more particles are engulfed; in cell and animal models the release of messengers by phagocytes shifts as a result.

   too little — If little CRP is bound, phagocytes recognise marked particles less often via this route and rely on antibodies, which bind to the same receptors.

   observed in studies · Source 4

7. C1q → C3b on the surface C1r, C1s, C4, C2 The cascade of complement proteins cleaves C3 and attaches C3b firmly to the surface. The particle is thus labelled for the immune defence. Phagocytes carry receptors for C3b. Source 3↑ supplies C3b is the actual marker: phagocytes carry receptors for it and so seize marked particles. The regulator factor H usually stops the chain at this point. established physiology Source 3, 2
   ⚖ When the balance tips

   too much — If a lot of C3b is attached, particles are more densely marked and engulfed faster; factor H keeps the chain from running further.

   too little — If little C3b is attached, cell debris stays unmarked for longer and is cleared more slowly.

   established physiology · Source 3, 2

8. C3b on the surface → Uptake by phagocytes Phagocytes recognise the markings, engulf the particle and break it down inside. With dead body cells the inflammatory response usually stays weak. Source 3, 4↓ depletes Phagocytes clear marked cell debris and bacteria and remove them from the tissue. With dead body cells this uptake proceeds without a strong inflammatory response. observed in studies Source 3, 4
   ⚖ When the balance tips

   too much — If very many particles are marked, the busy phagocytes release more messengers, including IL-6; this can restart the pathway via the liver.

   too little — If few particles are engulfed, cell debris lingers longer, and its components can keep acting as a stimulus for the immune defence.

   observed in studies · Source 3, 4, 1

9. Fcγ receptors → Uptake by phagocytes Phagocytes recognise the markings, engulf the particle and break it down inside. With dead body cells the inflammatory response usually stays weak. Source 3, 4↓ depletes Phagocytes clear marked cell debris and bacteria and remove them from the tissue. With dead body cells this uptake proceeds without a strong inflammatory response. observed in studies Source 3, 4
   ⚖ When the balance tips

   too much — If very many particles are marked, the busy phagocytes release more messengers, including IL-6; this can restart the pathway via the liver.

   too little — If few particles are engulfed, cell debris lingers longer, and its components can keep acting as a stimulus for the immune defence.

   observed in studies · Source 3, 4, 1

Further stations

• Interleukin-6 — Immune cell messenger When tissue is irritated, macrophages and other cells release the messenger interleukin-6. It travels with the blood to the liver. The more of it arrives, the more CRP the liver makes. Source 1↑ supplies IL-6 is the signal on which the liver makes CRP: the more of it arrives, the more CRP is formed. At the same time it stimulates other acute-phase proteins there and slows the production of albumin. established physiology Source 1
  ⚖ When the balance tips

  too much — If IL-6 is produced persistently instead of fading once the irritation ends, the liver's production of CRP and other acute-phase proteins also stays switched on.

  too little — If little IL-6 is present, the liver receives hardly any signal and makes little CRP; the same is described when the IL-6 receptor is occupied by tocilizumab.

  established physiology · Source 1, 5

• Binding phosphocholine — only with calcium Each subunit has a pocket into which phosphocholine fits with the help of two calcium ions. This building block is exposed on damaged cell membranes and on some bacteria. Without calcium the binding comes apart. Source 2, 3↑ supplies Binding is the recognition step: CRP attaches where phosphocholine is exposed, that is to damaged cells and some bacteria, not to intact cells. Without calcium the binding comes apart. established physiology Source 2, 3
  ⚖ When the balance tips

  too much — If many binding sites are exposed, many CRP rings attach; on damaged membranes the ring can break apart into single subunits that act differently from the ring.

  too little — If little CRP is present, exposed binding sites stay unoccupied, and cell debris and bacteria are marked less along this route.

  observed in studies · Source 3, 2

Cofactors in this pathway

• Calcium — Two calcium ions per subunit enable CRP to bind phosphocholine; without calcium the binding comes apart Source 2, 3In the ORY catalogue as a laboratory value: Calcium (intrazellulär)
• Choline — Building block of phosphocholine, to which CRP binds on membranes and bacteria; only exposed sites are recognised Source 2, 3
• Magnesium — Forms the Mg-ATP complex with ATP that JAK kinases use as their phosphate source; so they pass on the IL-6 signal Source 6, 1In the ORY catalogue as a laboratory value: Magnesium
• ATP (adenosine triphosphate) — Supplies JAK kinases with the phosphate group they attach to STAT3; only then does STAT3 move into the nucleus Source 1

What acts on this pathway

• Tocilizumab — Tocilizumab occupies the IL-6 receptor, so the messenger can no longer reach the liver cell. The prescribing information describes that blood CRP levels fall while it is in use. Source 5

Sources

1. Tanaka T, Narazaki M, Kishimoto T. IL-6 in inflammation, immunity, and disease. Cold Spring Harb Perspect Biol 2014 · PubMed 25190079
2. Black S, Kushner I, Samols D. C-reactive Protein. J Biol Chem 2004 · PubMed 15337754
3. Sproston NR, Ashworth JJ. Role of C-Reactive Protein at Sites of Inflammation and Infection. Front Immunol 2018 · PubMed 29706967
4. Lu J, Mold C, Du Clos TW, Sun PD. Pentraxins and Fc Receptor-Mediated Immune Responses. Front Immunol 2018 · PubMed 30483265
5. US prescribing information Tocilizumab (DailyMed), section 12.2 Pharmacodynamics · Prescribing information
6. de Baaij JH, Hoenderop JG, Bindels RJ. Magnesium in man: implications for health and disease. Physiol Rev 2015 · PubMed 25540137

Whole pathway: CRP

Related pathways

• ANCA against MPO and PR3 — fcγ receptors
• HbA1c and insulin — Calcium (intrazellulär), Magnesium
• Vitamin D — Calcium (intrazellulär), Magnesium
• Zonulin and gut barrier — Calcium (intrazellulär), Magnesium

As of 2026-09-16. Draft written by Claude to schema v2; sources checked in PubMed; expert review pending
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