ABSTRACT
In the ¡rst half of the nineteenth century, advances in microscopy enabled scientists to examine many different tissues at the cellular level, including nervous tissue, of which Purkinje neurons were the ¡rst cells described. In 1846, Virchow ¡rst used the term neuroglia, noting that the area surrounding neurons resembled connective tissue formed by a sort of cement (glia) in which the nervous system elements
4.1 Historical Overview of Astrocytes ............................................................... 107 4.2 CNS: To Be or Not to Be Immune Privileged? ............................................. 108 4.3 Pattern Recognition Receptors (PRRs)......................................................... 109
4.3.1 TLR Expression in Astrocytes.......................................................... 110 4.3.2 Mannose and Scavenger Receptors in Astrocytes ............................ 115 4.3.3 Astrocytes and Complement Receptors ............................................ 117 4.3.4 Cytoplasmic PRRs in Astrocytes ..................................................... 118 4.3.5 Astrocytes and Secreted PRRs ......................................................... 120
4.4 Consequences of PRR Signaling in Astrocytes ............................................ 120 4.5 Blood-Brain Barrier (BBB), Astrocytes, and In¢ammation ........................ 122 4.6 Summary/Perspectives .................................................................................124 Acknowledgments .................................................................................................. 125 References .............................................................................................................. 125
were embedded. Otto Deiters (1834-1863) is considered the ¡rst scientist who provided illustrations of a cell type that resembles our modern view of astrocytes. In the 1870s, Camillo Golgi described the diversity of glial cells in gray and white matter and characterized them as roundish, oval, or star-shaped cells, from which numerous long, ¡ne, and never arborized prolongations originate. In addition, he was able to show the structural association of astrocytes with blood vessels; however, their involvement in the blood-brain barrier (BBB) would require several decades to become established. In 1893, Micheal von Lenbossek introduced the term astrocyte to refer to the star-shaped neuroglial cells. Once astrocytes and neurons were recognized as unique cell types in the early 1900s, this sparked the interest of scientists who pondered their possible link to brain diseases. During this time, improvements in electrophysiological techniques made neurons the primary cell of interest, resulting in neuroglia being largely overlooked. Therefore, until recent decades astrocytes were considered to be supportive cells only.
