S100 Calcium Binding Protein A8 (S100A8) is a member of the S100 family of proteins containing 2 EF-hand calcium-binding motifs. S100 proteins are localized in the cytoplasm and/or nucleus of a wide range of cells, and involved in the regulation of a number of cellular processes such as cell cycle progression and differentiation. S100 genes include at least 13 members which are located as a cluster on chromosome 1q21. S100A8 may function in the inhibition of casein kinase and as a cytokine. Altered expression of S100A8 is associated with the disease cystic fibrosis.