Calprotectin, a member of the widespread calcium-binding S-100 protein family, is present in remarkably high concentration in the cytoplasm of human neutrophils. The calprotectin molecule is composed of light (MRP8) and heavy (MRP14) subunits. Although not secreted from intact neutrophils, calprotectin release from dead and dying neutrophils creates high concentrations of the protein in inflammatory or abscess fluids and in the intestinal tract lumen of patients with inflammatory bowel disease.

> 95% as determined by Bis-Tris PAGE; > 90% as determined by HPLC