The monoclonal antibody 697 reacts with human neutrophil lipocalin (HNL), also known as human nGAL (25 kDa). Lipocalins are a widespread family of small, robust proteins that typically transport or store biological compounds which are either of low solubility or are chemically sensitive, including vitamins, steroids, odorants and metabolic products.The members of this lipocalins share a high similarity in their tertiary structures in spite of a low degree in amino-acid sequence identity: three highly conserved sequence motifs form a funnel-like beta barrel which encloses a hydrophobic pocket for the internal ligand binding.The human neutrophil lipocalin (HNL) is produced by neutrophil leukocytes and stored in intracellular specific granules. Neutrophil lipocalin is covalently linked to gelatinase B (MMP-9) and proMMP is stored in three forms: the monomeric form (92 kDa), the homodimer (220 kDa) and a heterodimer (125 kDa).During inflammation and neoplastic transformation the human neutrophil lipocalin (HNL) is produced in neutrophils and in epithelial cells. Furthermore neutrophil lipocalin is a superior means to distinguish acute bacterial and viral infections as well as it enables the determination of the neutrophil activation level.