Human S100A12: a novel key player in inflammation?

S100A12 is a member of the S100 family of EF-hand calcium-binding proteins. Human S100A12 is predominantly expressed and secreted by neutrophil granulocytes and, therefore, has been assigned to the S100 protein subfamily of calgranulins or myeloid-related proteins. Intracellular S100A12 exists as an anti-parallel homodimer and upon calcium-dependent activation interacts with target proteins to regulate cellular functions. Extracellular S100A12 exists majorily as homodimer and hexamer, respectively, and shows cytokine-like characteristics. It is part of the innate immune response and linked to certain autoimmune reactions. Human S100A12 is markedly overexpressed in inflammatory compartments, and elevated serum levels of S100A12 are found in patients suffering from various inflammatory, neurodegenerative, metabolic, and neoplastic disorders. In this regard, interaction of calcium-activated S100A12 with the multiligand receptor for advanced glycation endproducts (RAGE) and its soluble form (sRAGE) plays a central pathogenetic role. Recent clinical evidence suggests a high potential of S100A12 as a sensitive and specific diagnostic marker of localized inflammatory processes.