S-100 is a low molecular weight protein expressed in glial cells, chondrocytes, macrophages, Langerhans cells, dendritic cells, adipocytes, keratinocytes and breast epithelial cells.
S-100 is involved in regulation of protein phosphorylation, calcium homeostasis, cell differentiation, and inflammatory response.
In clinical diagnostics, S-100 protein expression is used as a marker of certain tumors, melanomas, peripheral nerve sheath tumors, and clear cell sarcomas.