GFAP (glial fibrillary acidic protein) is an intermediate filament protein found in the central nervous system. Functionally, GFAP helps maintain cell shape and astrocyte mechanical strength, as well as participate in cell communication and blood brain barrier function. In immunohistochemistry, it is positive in astrocytes, ganglion cells and some ependymal cells of the central nervous system. In cancer, it is positive in ependymomas and in astrocytic tumors such as astrocytic gliomas, astrocytomas and glioblastomas. References: Brain Research. 2007 July. 1158: 103–15. doi:10.1016/j.brainres.2007.04.070, PMID: 17555726; Neurology India. 2013. 61 (4): 383–8, PMID: 24005729; The Journal of Cell Biology. 1991 Mar. 112 (6): 1205–13. doi:10.1083/jcb.112.6.1205, PMID: 1999469; Neurosci Lett. 1996 May 3;209(1):29-32, PMID: 8734902.