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various factors. If this could be accomplished in humans, it might be possible to promote recovery of function in people with MS.

Astrocytes: Glial Cells Are More than “Glue”

Astrocytes are star-shaped glial cells that do not form myelin. They have traditionally been viewed only as “scarring” elements in multiple sclerosis. Yet there is evidence that these cells are much more complex than this. Astrocytes are capable of presenting antigens and promoting T-cell proliferation, which indicates that they might play a role in reactivation and regulation of inflammatory process in the brain.2,16,46 They may play an important role in the etiopathogen-

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FIGURE 5.2 Possible role of AMPA/kainate receptors on neurons and glia. Activation of T lymphocytes (in this case, a T lymphocyte reactive to the brain-specific loop of the myelin protein, PLP [proteolipid protein]), macrophages, and resident microglia at the site of inflammation in the white matter of the central nervous system causes release of glutamate. The increased extracellular glutamate binds to AMPA/kainate receptors on neurons and on oligodendrocytes. This leads to increased calcium fluxes and death of oligodendrocytes and neurons. NOTE: MHC = major histocompatibility complex. SOURCE: Steinman L, 2000.89 Reprinted with permission.

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