GFAP, a class-III intermediate filament, is a cell-specific marker that, during the development of the central nervous system, distinguishes astrocytes from other glial cells. In particular, vimentin filaments are present at early developmental stages, while GFAP filaments are characteristic of differentiated and mature brain astrocytes. In addition, GFAP intermediate filaments are also present in nonmyelin-forming Schwann cells in the peripheral nervous system.