C-reactive protein (CRP) was originally discovered by Tillett and Francis in 1930 as a substance in the serum of patients with acute inflammation that reacted with the C polysaccharide of pneumococcus. CRP is a 224 residue protein with a monomer molecular mass about 25 kDa and pI 6.4. Monomers are noncovalently associated into pentameric structure.
For decades CRP had been known as liver-derived protein. However recent data showed significant level of CRP expression in other tissues, such as blood vessel wall and coronary artery smooth muscle cells, where CRP is supposed to be presented as a monomer (mCRP), while native pentameric protein (nCRP) is predominantly found in plasma.
Exact function of CRP in human organism is still under discussion. This protein has been shown to participate in inflammatory as well as innate immunity processes. Important bioactivities of CRP are determined by its ability to bind a variety of ligands, such as damaged cell membranes, apoptotic cells, fibronectin, etc, with highest affinity to phosphocholine residues. When CRP is ligand-bound, it could be recognized by complement component C1q, whereby activates classical complement pathway. Via interaction with complement factor H, CRP regulates the alternative complement pathway.
C-reactive protein is accepted in clinical use as the major, although rather non-specific, marker of inflammation. In generally healthy subjects CRP levels are usually less than 5 mg/L. Highest levels of CRP are observed in bacterial infection, such as septic arthritis, meningitis and pneumonia. Mildly elevated CRP has been described after myocardial infarction and other types of tissue damage. In 2003, the Centers for Disease Control and Prevention (CDC) and the American Heart Association (AHA) issued a statement identifying CRP as the inflammatory marker best suited for use in current clinical practice to assess cardiovascular risk. Many epidemiologic studies have indicated that CRP is a strong independent predictor of future cardiovascular events, including myocardial infarction, ischemic stroke, peripheral vascular disease, and sudden cardiac death without known cardiovascular disease. The CDC/AHA guidelines support the use of CRP in primary prevention and set cutoff points according to relative risk categories. That’s why present day high sensitivity CRP (hsCRP) assays are aimed at nanogram per milliliter CRP level distinction, and abbreviation hsCRP now is accepted name of the detected protein in such assays. The significant relationship between plasma hsCRP and the risk of death in patients with the acute coronary syndrome has been shown. Furthermore, it has been reported that increased circulating hsCRP concentrations are associated with an increased risk of death from several widespread chronic disease.
In native CRP molecule each protomer has two coordinated Ca2+ ions. Here at AdvancedImmunoChemical, we offer anti-CRP MAbs which are either sensitive or insensitive to the absence of Ca2+ in the solution. Some of our antibodies recognize antigen only in the presence of Ca2+ (MAbs C3, C4). The most part of MAbs do not depend of Ca2+ presence in sandwich immunoassay and are able to efficiently recognize antigen even in the presence of EDTA in the tested sample. Our best antibody pairs provide 10,000-fold linearity in experimental immunofluorometric assays. These antibody combinations could be used for the development of hsCRP assays for different diagnostic platforms. In conventional CRP assays turbidimetry and competitive assay techniques are often applied. In such assays relatively low affinity of utilized MAbs is usually preferable. We offer monoclonal antibodies with different affinities, allowing for their utilization in different types of immunoassays.
We offer over ten different monoclonal antibodies specific to human CRP. The majority of these mAbs are unaffected by the presence or absence of Ca2+ in the quantitative detection of CRP. However, some antibodies and antibody pairs depend on Ca2+ and the binding of CRP may be abolished in the presence of EDTA. This should be kept in mind when designing a CRP immunoassay. We also supply purified native CRP and CRP-free serum. For more information, please see hs-CRP AssayNotes.
Effect of EDTA on CRP measurements. In this sandwich immunoassay, pair C3-C6 (left) shows a dependence on Ca2+ as it fails to recognize CRP in the presence of EDTA. In contrast, pair C5-CRP135 is unaffected by EDTA in the solution.
High-sensitivity CRP (hsCRP)
It should be noted that CRP is also used as a marker of increased risk for cardiac diseases. In this, it is the basal level of CRP that has more clinical significance and therefore, the assays need to be highly sensitive and aimed at nanogram per milliliter CRP level distinction. Our anti-CRP antibodies are suitable for the development of a quantitative hsCRP assay.
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- Sin K.K. at al. “Fluorogenic nanocrystals for highly sensitive detection of CRP.” IEE Proc Nanobiotechnology 2006 June; 153(3): 54-58.
- Biro A. et al. “Studies on the interactions between CRP and complement proteins.” Immunology 2007 May; 121(1): 40-50.
- Ridker P.M. “CRP: a simple test to help predict risk of heart attach and stroke.” Circulation 2003; 108:e81-e85.
Anne Tolles, M.Sc./President