S100A9A gene on chromosome 1q21 that encodes a member of the S100 family of proteins, which contain 2 EF-hand calcium-binding motifs and as a group regulate cell cycle progression and differentiation and other cellular processes. S100A9 has antimicrobial activity against bacteria and fungi and provides resistance to invasion by pathogenic bacteria, and it upregulates transcription of genes under the control of NF-kappa-B; it is linked to the endotoxic shock response to bacterial lipopolysaccharide. S100A9 promotes tubulin polymerisation and macrophage and granulocyte migration and infiltration into wound sites; it is a pro-inflammatory mediator and upregulates IL8 release and cell surface expression of ICAM1. Extracellular S100A9 (calprotectin) binds to target cells and promotes apoptosis.
Altered expression of S100A9 is linked to cystic fibrosis.