The proteins S100A8 and S100A9 form a heterodimer called calprotectin.

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.

This protein may function in the inhibition of casein kinase and as a cytokine.

Altered expression of this protein is associated with the disease cystic fibrosis [5] and post COVID-19 condition.