Cellular reactions of the central nervous system.

Major cell types of the central nervous system comprise neurons, glial cells (astrocytes, oligodendrocytes, ependymal cells, and microglia), choroid plexus cells, cells related to blood vessels and coverings. These cells show a wide range of reactions to various noxious agents, which can be detected in routine stainings. Some of these reactions are nonspecific to different injuries; however some, such as the appearance of inclusion bodies, can be highly disease-specific. Immunohistochemical markers are widely used in neuropathologic diagnostic practice and help to understand the pathogenesis of diseases. The most widely used neuronal markers comprise phosphorylated and nonphosphorylated neurofilaments, microtubule-associated protein-2, NeuN, or synaptic markers such as synaptophysin. The best antibody for the detection of astrocytes is anti-GFAP (glial fibrillar acidic protein); however, to support a glial origin, S100 or vimentin is also used in the diagnostic practice. Further astroglial markers include connexin-43, excitatory amino acid transporters, aquaporin-4, heat shock protein Hsp27, and α-B-crystallin. Depending whether the tissue is fixed or nonfixed, different oligodendroglial markers are available, such as myelin basic protein, myelin oligodendrocyte glycoprotein, myelin-associated glycoprotein, proteolipid protein, Olig2, NG2, 2' 3'-cyclic nucleotide 3-phosphodiesterase (CNPase), and tubulin polymerization-promoting protein/p25 alpha (TPPP/p25). A wide range of microglia functions is recognized. Apart from a role in immune-mediated disorders, inflammation, and response to injury, microglia are important during the development and aging of the brain. The best markers include the clone CR3/43, Iba1, and CD68. Evaluation of cell reactions is the first step in the diagnostic procedure.