Theiler's virus infection of perforin-deficient mice

Abstract

Theiler's virus, a murine picornavirus, infects the central nervous systems of C57BL/6 mice and is cleared after approximately 10 days by a process which requires CD8+ cytotoxic T cells. We used perforin-deficient C57BL/6 mice to test the role of this protein in viral clearance. Perforin-deficient mice died from viral encephalomyelitis between days 12 and 18 postinoculation. They had high levels of viral RNA in their central nervous systems until the time of death. In contrast, viral RNA had disappeared by day 11 postinoculation in wild-type C57BL/6 mice. Cytotoxic T cells can kill infected cells by two main mechanisms: the secretion of the pore-forming protein perforin or the interaction of the Fas ligand with the apoptosis-inducing Fas molecule on the target cell. Our results demonstrate that clearance of Theiler's virus from the central nervous system in C57BL/6 mice is perforin dependent.

FIG. 1

Clinical symptoms and mortality in infected perforin-deficient (•) and C57BL/6 wild-type (▴) mice. Mice were infected intracerebrally with 10⁴ PFU of the DA strain of Theiler’s virus and were observed daily for signs of encephalomyelitis (A) and survival (B).

FIG. 2

Amounts of viral RNA present in the brains of C57BL/6 wild-type and perforin-deficient (perforin −/−) mice 8 and 11 days after inoculation with 10⁴ PFU of Theiler’s virus. Viral RNA was quantitated with a dot blot assay as described in the text. The ordinate shows, for each mouse, the highest dilution of the RNA solution which gave a positive hybridization signal. Each symbol represents one mouse.

FIG. 3

(A) Viral antigens, inflammation, and tissue destruction in the brain (hippocampus) of a perforin-deficient mouse on day 8 p.i. Arrows point to examples of neurons containing viral antigens. Final magnification, ×427. (B) Viral antigens in a large motoneuron of the spinal cord (arrow) and intense inflammation in a perforin-deficient mouse on day 8 p.i. Final magnification, ×427. (C) Large amount of viral antigens, tissue destruction, and inflammation in the hippocampus of a perforin-deficient mouse on day 11 p.i. Final magnification, ×267. (D) Infected cell (arrow) and inflammation in the white matter of a perforin-deficient mouse on day 18 p.i. Final magnification, ×427.

FIG. 4

(A) Viral antigens, inflammation, and tissue destruction in the hippocampus of a control C57BL/6 mouse on day 8 p.i. Arrows point to neuron cell bodies containing viral antigens. (B) An inflammatory infiltrate (star) in the gray matter of the spinal cord of a control C57BL/6 mouse on day 8 p.i. No viral antigen is present. Final magnification for both panels, ×427.