S100B is a small calcium-binding protein in the neuronal system, and belongs to the S100 family. S100B proteins are a family of 25 homologous intracellular calcium-binding proteins characterized by EF hand motifs, low molecular weights (9–13 kDa), ability to form homodimers, heterodimers and oligomeric assemblies, and are characterized by tissue and cell-specific expression.  They are solely present in vertebrates. S100B protein is mainly expressed in the neuronal system such as astrocytes, maturing oligodendrocytes, dendritic cells, and Schwann cells. However, some other cells outside the brain, like kidney epithelial cells, ependymocytes, chondrocytes, adipocytes, and melanocytes, can also express S100B protein.