Sindbis virus is an alphavirus that produces an acute nonfatal encephalitis in mice. The local immune responses to this virus are both cellular and humoral. The cellular response is characterized by an infiltration of mononuclear cells into the cerebrospinal fluid (CSF), the meninges, and the brain parenchyma. This inflammatory response is initiated by sensitized T-lymphocytes that are stimulated by exposure to viral antigen to produce a lymphokine, which is chemotactic for mononuclear cells. These T-cells may also produce a lymphokine that stimulates mast cells to release vasoactive amines, which facilitate monocyte entry from the blood. Inflammation is not necessary for clearance of virus from the brain. Humoral immune responses are initially systemic and, in the central nervous system (CNS), reflect transudation of serum antibody. During recovery, there is local production of antiviral IgA as well as IgG.
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