[Study Notes] C-Reactive Protein

🥼 Practice and Clinical
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Overview

Discovered in 1930 in the serum of patients with pneumococcal pneumonia, it can bind to capsular polysaccharide and was initially mistaken for an antibody (which it actually is not), hence named C-reactive protein (CRP).

It is an acute phase reactant protein that reacts with the C-polysaccharide of Streptococcus pneumoniae.

Mainly produced by the liver, it is widely present in serum and other body fluids, with functions including complement activation, promotion of phagocytosis, and immune modulation.

Physiology

Elevation

  • Pathogen-associated molecular patterns (PAMPs)

  • Damage-associated molecular patterns (DAMPs)

  • Mainly produced by the liver; CRP decreases in liver failure.

    • Production promoted by IL-6 and IL-1
    • Inhibited by IFNα

  • Binds to pathogens/tissues

    • A face (binding site) is calcium-dependent and binds to:
      • [[oxidized low-density lipoprotein (oxLDL)]]
      • [[LOX-1]]
      • [[phosphatidylcholine (PC)]]
    • B face (effector site)
      • Binds complement ([[C1q]], [[FcγR]])

  • Monomer/pentamer

    • Bacteria generally form pentamers

Metabolism

Half-life of 19 hours. Increases within 4-6 hours after infection, doubling approximately every 8 hours, peaking at about 48 hours.

Each subunit of the pentamer has one phosphatidylcholine binding site (binding activates the classical complement pathway).

Reference Values

Immune diffusion method: serum < 10 mg/L.

Clinical Significance

  • CRP measurement is important for diagnosis and therapy monitoring in inflammation, tissue injury, malignant tumors, and other diseases.
    1. Elevated in early stages of various acute suppurative inflammations, bacteremia, tissue necrosis, malignant tumors, etc.
    2. Serves as a differential marker between bacterial and non-bacterial infections, and between organic and functional diseases; CRP is generally elevated in bacterial infections and organic diseases.
  • Cardiac biomarker (3 mg/L as the threshold; the higher, the greater the risk)
  • Recommended not to be used to determine whether infection is present but to distinguish infection severity

Educational Video

https://www.bilibili.com/video/BV1QY411j7dc