Calprotectin is a heterodimer of the two calcium-binding proteins Calgranulin A (S100A8) and Calgranulin B (S100A9), also called Myeloid Related Protein (MRP) 8/MRP14. These non-covalently associated proteins constituted about 45% of the protein content of neutrophils cytosol and are 40-fold more abundant in neutrophils versus monocytes (Edgeworth et al., 1991). MRP8/14 is also present in macrophages of rheumatoid polyarthritic synovialis but not in normal tissue macrophages (Odink et al., 1987). This heterodimer belong to the alarmin family. Alarmins are released upon tissue injury and promotes inflammation.
Since MRP8/14 is locally released from damaged or inflamed tissues, it has been regarded as a biomarker. MRP8/14 has been shown to be a useful biomarker in sepsis, auto-immunes diseases, respiratory diseases, Kawasaki disease, inflammatory bowel syndrome (fecal calprotectin) and multiple sclerosis (Chan et al., 2012).
MRP8/14 assay is a solid phase enzyme linked immunoassay which has been validated in the laboratory for measurement in human serum.
Chan, J.K., Roth, J., Oppenheim, J.J., Tracey, K.J., Vogl, T., Feldmann, M., Horwood, N., and Nanchahal, J. (2012). Alarmins: awaiting a clinical response. J. Clin. Invest. 122, 2711–2719.
Edgeworth, J., Gorman, M., Bennett, R., Freemont, P., and Hogg, N. (1991). Identification of p8,14 as a highly abundant heterodimeric calcium binding protein complex of myeloid cells. J. Biol. Chem. 266, 7706–7713.
Odink, K., Cerletti, N., Brüggen, J., Clerc, R.G., Tarcsay, L., Zwadlo, G., Gerhards, G., Schlegel, R., and Sorg, C. (1987). Two calcium-binding proteins in infiltrate macrophages of rheumatoid arthritis. Nature 330, 80–82.