The mononuclear inflammatory response to Sindbis virus infection of the central nervous system is analogous to the cutaneous delayed-type hypersensitivity reaction. It is dependent on sensitized T cells for initiation, but many of the cells present are nonsensitized bone marrow-derived cells. Tissue mast cells have been shown to be important for the development of the delayed-type hypersensitivity reaction in the skin where capillary endothelial cells are joined by tight junctions. To determine whether mast cells are also important for the development of an immune-mediated inflammatory response across the endothelial tight junctions of the blood-brain barrier, the development of mononuclear inflammation in the central nervous system of reserpine-treated mice and mast cell-deficient mice (WBB6F1-W/Wv) was studied after infection with Sindbis virus. Three central nervous system compartments, the cerebrospinal fluid, the meninges, and the brain parenchyma, were evaluated for inflammation by counting the number of cells present, by grading the histopathologic lesions, and by labeling infiltrating cells with 125IUDR. By all parameters inflammation was reduced when mice were treated with reserpine or were deficient in mast cells. Antigen-specific humoral and cellular immune responses were depressed and virus clearance delayed in reserpine-treated mice, but not in mast cell deficient mice. It is concluded that the vasoactive amines released by mast cells in the central nervous system play a facilitating role in the development of the inflammatory response to Sindbis virus.
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