Figure 1.

Neutrophil granulocytes release both calprotectin [CP] and human neutrophil elastase [HNE]. A] Inactive neutrophils express CP and HNE, where CP is passively released. B] Upon activation, the neutrophils will initiate the process of neutrophil extracellular trap [NET] formation, which releases CP and HNE in huge amounts into the extracellular space, where HNE will begin to degrade the surrounding tissue and proteins, including CP. C] CP is cleaved by HNE, and small HNE-derived CP neo-epitope protein fragments [CPa9-HNE] are released into the blood and intestinal lumen and can be quantified by ELISA using protein fingerprint technology. D] Simplified depiction of how HNE cleaves CP and how specific monoclonal antibodies recognise only the specific HNE-derived CP neo-epitope fragment. ELISA, enzyme-linked immunosorbent assay.