CD4(+) and CD8(+) T cells make discrete contributions to demyelination and neurologic disease in a viral model of multiple sclerosis

Abstract

Following intracerebral infection with Theiler's murine encephalomyelitis virus (TMEV), susceptible strains of mice (SJL and PLJ) develop virus persistence and demyelination similar to that found in human multiple sclerosis. Resistant strains of mice (C57BL/6) clear virus and do not develop demyelination. To resolve the controversy about the role of CD4(+) and CD8(+) T cells in the development of demyelination and neurologic deficits in diseases of the central nervous system, we analyzed TMEV infection in CD4- and CD8-deficient B6, PLJ, and SJL mice. Genetic deletion of either CD4 or CD8 from resistant B6 mice resulted in viral persistence and demyelination during the chronic stage of disease. Viral persistence and demyelination were detected in all strains of susceptible background. Although genetic deletion of CD8 had no effect on the extent of demyelination in susceptible strains, deletion of CD4 dramatically increased the degree of demyelination observed. Whereas strains with deletions of CD4 showed severe neurologic deficits, mice with deletions of CD8 showed minimal or no deficits despite demyelination. In all strains, deletion of CD4 but not CD8 resulted in a decreased delayed-type hypersensitivity response to viral antigen. We conclude that each T-cell subset makes a discrete and nonredundant contribution to protection from viral persistence and demyelination in resistant strains. In contrast, in susceptible strains, CD8(+) T cells do not provide protection against chronic demyelinating disease. Furthermore, in persistent TMEV infection of the central nervous system, neurologic deficits appear to result either from the absence of a protective class II-restricted immune response or from the presence of a pathogenic class I-restricted response.

FIG. 1

Spinal cord cross sections from 45-day-infected B6 (A through C) and PLJ (D through F), wild-type (A and D) CD4-deficient (B and E), or CD8-deficient (C and F) mice. Glycolmethacrylate-embedded sections were stained with erichrome/cresyl violet stain. White matter appeared normal in B6 (+/+) (A) and B6 CD4 (−/−) (B) mice. Focal demyelinating lesions were present in B6 CD8 (−/−) (C), PLJ (+/+) (D), and PLJ CD8 (−/−) (F) mice, and massive demyelination was found in PLJ CD4 (−/−) mice (E).

FIG. 2

Spinal cord cross sections from mice infected for 90 days demonstrates demyelination in B6 CD4 (−/−) mice (A) and more severe demyelination in PLJ CD4 (−/−) mice (B).

FIG. 3

Pathology scores in brain (Crb, cerebellum; Bst, brain stem; Cor, cortex; Hip, hippocampus; Stm, striatum; CCo, corpus callosum; Men, meninges) in C57BL/6, SJL, and PLJ mice infected with TMEV for 45 days. Mice with genetic deletion of CD4 (CD4 −/−) or CD8 (CD8 −/−) were compared to heterozygote CD4 +/− (open circles) or CD8 +/− (solid circles) or wild-type (+/+) mice of each strain.

FIG. 4

Titers of infectious virus isolated by plaque assay from the CNS (brain and spinal cord) of mice infected with TMEV for 7 days (A, C, and E) or 45 days (B, D, and F). Mice with genetic deletion of CD4 [CD4 (−/−)] or CD8 [CD8 (−/−)] are compared to heterozygote [CD4 (+/−) or CD8 (+/−)] littermate or wild-type (+/+) mice. Dashed lines represent the sensitivity of the assay. Data are expressed as log₁₀ PFU per gram of CNS tissue.

FIG. 5

Theiler’s virus-specific antibody in the sera of mice infected with virus for 45 days. C57BL6, SJL, and PLJ mice with genetic deletion of CD4 (CD4 −/−) or CD8 (CD8 −/−) were compared to heterozygote (CD4 +/− or CD8 +/−) littermate controls or wild-type (+/+) mice. Results from serum of uninfected wild-type SJL mice are shown for comparison.

FIG. 6

TMEV-specific DTH responses were elicited by intradermal ear injection with 10 μl of UV-inactivated virus (2 × 10⁸ PFU/ml). Immediately before antigen challenge, and 24 and 48 h after antigen challenge, ear thickness was measured and expressed as 10⁻² millimeters. Error bars indicate the standard error of the mean.