CRP: the pathway in the body

This page shows the biochemical pathway behind the laboratory value hsCRP (high-sensitivity C-reactive protein): which stations follow one another, which enzymes carry out each step and which cofactors they use. Every statement has a source. The page describes general textbook knowledge and says nothing about any individual person.

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.

The pathway step by step

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. Source 1
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. 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. Source 2
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. Source 2, 3
5. Binding phosphocholine → C1q The bound face of the ring holds on to C1q, the first component of the classical complement pathway. 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. 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. Source 3
8. C3b on the surface → Uptake by phagocytes Phagocytes recognise the markings, engulf the particle and break it down inside. Source 3, 4
9. Fcγ receptors → Uptake by phagocytes Phagocytes recognise the markings, engulf the particle and break it down inside. Source 3, 4

Cofactors in this pathway

• Calcium — Two calcium ions per subunit enable CRP to bind phosphocholine 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 Source 2, 3
• Magnesium — Forms the Mg-ATP complex with ATP that JAK kinases use as their phosphate source 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 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

Related pathways

• 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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