> See also: > - Reference # C-Reactive Protein (CRP) **C-Reactive Protein (CRP)** performs many of the functions that antibodies do (but lacking their specificity): - Opsonization - Binds to receptors on *phagocytic cells* (macrophages, neutrophils, monocytes) to promote phagocytosis. - Agglutination - Precipitation - Activation of complement (via classical pathway) Because of this, CRP plays a major role in the innate immune system and defends against pathogens until specific antibodies can be produced by the adaptive immune response. ### Structure & Production CRP is composed of 5 identical subunits held together by *non-covalent* bonds. It is primarily synthesized in [[the liver]] and there will always be trace amounts (although possibly not detectable) within serum samples. ## Associated Conditions - Heart disease and myocardial infarction (heart attack) - Bacterial & Viral Infections - Tuberculosis (TB) - [[Autoimmunity]] (RA & SLE) - Collagen Diseases (Scleroderma) - Malignant Diseases (Cancer) ### Role in Inflammation > See also: [[Inflammation & Fevers]] CRP is *highly associated with acute inflammation* and is the most widely used marker for it. - There is a *rapid increase 4-6 hours* following *infection, surgery, or physical trauma* - There can be up to a *100-1000x fold increase*, with levels *peaking within 24-72 hours* Common markers of inflammation are: - Pain, Heat, Redness, and Swelling (Edema) ### Testing Methods The presence of CRP can be qualitatively analyzed through latex agglutination. - The latex particle is coated with **anti-CRP** *(IgM, Known Antibody)* which will bind to any **CRP** *(Unknown Antigen)* present within the serum. > **Reagents:** > - *Latex particles* coated with anti-human CRP is the *visualizing agent*. > - *Positive Control:* Human serum with $\ge$ 6 mg/L CRP > - *Negative Control:* Human serum with < 6 mg/L CRP --- A positive result should appear to have a noticeable clumping around the edges (agglutination). - This indicates that CRP is present. > **False Positives:** > - Bacterially contaminated sera > - Sera containing elevated levels of rheumatoid factor (RF) > - First trimester of pregnancy expected to have elevated CRP levels > - Oral contraceptives and intrauterine devices can cause elevated CRP levels --- A negative result should appear to have a smooth/homogeneous suspension with no clumping/agglutination. - This indicates the absence of CRP. > **False Negatives:** > Reactions are weaker between 200-400 mg/L. > >If CRP concentration is above 400 mg/L, the sample should be diluted before performing the test, otherwise it will likely result in a false negative.