The mouse S100A9/Calprotectin ELISA will detect murine S100A9 homodimers as well as higher molecular oligomers, including the S100A8/A9 heterocomplex.S100 proteins are low molecular weight calcium binding proteins. The family consists of22 members to date that are expressed in several tissues and cell types and have diverse functions. Murine S100A9, also called calgranulin B or MRP14, has a molecular weight of approximately 13kD. S100 proteins consist of 2 (calcium binding) EF-hands located on the termini flanked by hydrophobic hinge regions. They are expressed in a cell type specific manner and with specific subcellular localization. Intracellular proteins can exist as dimers. S100A9 can form homodimers but is often associated with S100A8 (MRP8) to form heterodimers, also well known as calprotectin. Intracellular function of S100 proteins includemodulation ofenzyme activity, calcium homeostasis, cell differentiation and survival. Extracellularly, they participate in signal transduction and interact with cell surface receptors like RAGE, TLRs and others.S100A9 is constitutively expressed by myeloid cells nut not by lymphocytes. It is highly expressed in resting neutrophils, keratinocytes, macrophages and epithelial cells in active inflammatory disease. S100A9 is a potent chemoattractant for neutrophils and monocytes. The expression can be induced by several mediators like LPS, TNFα, IL-1, IL10 an TGFβ depending on the expressing cell type. The protein is predominantly associated with (chronic) inflammation. Elevated serum levels are found among others in patients with cystic fibrosis, inflammatory bowel diseases, rheumatoid arthritis, cardiovascular disease and malignancies.