Glial fibrillary acidic protein (GFAP) is a type III intermediate filament protein that is a key structural element of the star-shaped glial cells known as astrocytes and some ependymal cells, which comprise the membranous lining of the ventricles of the brain and the spinal cord's central canal. When astrocytes of the brain are injured, the cells respond by increasing their numbers through astrogliosis, an event that closely correlates with increased GFAP expression. Glial fibrillary acidic protein associates with the annexin II-p2 and S-100 proteins, which together with phosphorylation regulate the polymerization of GFAP. The intermediate filament protein can be readily targeted for the purposes of fluorescence microscopy through immunofluorescent labeling involving antibodies. It is interesting to note that antibodies to GFAP have been reportedly detected in human subjects suffering from dementia.

The adherent log phase culture of rat enteroglial cells presented in the digital image above was immunofluorescently labeled with primary anti-GFAP mouse monoclonal antibodies followed by goat anti-mouse Fab fragments conjugated to Cy3. The culture was also stained for DNA with Hoechst 33258 and for F-actin with Alexa Fluor 488 conjugated to phalloidin. Images were recorded in grayscale with a QImaging Retiga Fast-EXi camera system coupled to an Olympus BX-51 microscope equipped with bandpass emission fluorescence filter optical blocks provided by Omega Optical. During the processing stage, individual image channels were pseudocolored with RGB values corresponding to each of the fluorophore emission spectral profiles.