T Cells Infiltrate the Brain in Murine and Human Transmissible Spongiform Encephalopathies†

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American Society for Microbiology

RESUMO

CD4 and CD8 T lymphocytes infiltrate the parenchyma of mouse brains several weeks after intracerebral, intraperitoneal, or oral inoculation with the Chandler strain of mouse scrapie, a pattern not seen with inoculation of prion protein knockout (PrP−/−) mice. Associated with this cellular infiltration are expression of MHC class I and II molecules and elevation in levels of the T-cell chemokines, especially macrophage inflammatory protein 1β, IFN-γ-inducible protein 10, and RANTES. T cells were also found in the central nervous system (CNS) in five of six patients with Creutzfeldt-Jakob disease. T cells harvested from brains and spleens of scrapie-infected mice were analyzed using a newly identified mouse PrP (mPrP) peptide bearing the canonical binding motifs to major histocompatibility complex (MHC) class I H-2b or H-2d molecules, appropriate MHC class I tetramers made to include these peptides, and CD4 and CD8 T cells stimulated with 15-mer overlapping peptides covering the whole mPrP. Minimal to modest Kb tetramer binding of mPrP amino acids (aa) 2 to 9, aa 152 to 160, and aa 232 to 241 was observed, but such tetramer-binding lymphocytes as well as CD4 and CD8 lymphocytes incubated with the full repertoire of mPrP peptides failed to synthesize intracellular gamma interferon (IFN-γ) or tumor necrosis factor alpha (TNF-α) cytokines and were unable to lyse PrP−/− embryo fibroblasts or macrophages coated with 51Cr-labeled mPrP peptide. These results suggest that the expression of PrPsc in the CNS is associated with release of chemokines and, as shown previously, cytokines that attract and retain PrP-activated T cells and, quite likely, bystander activated T cells that have migrated from the periphery into the CNS. However, these CD4 and CD8 T cells are defective in such an effector function(s) as IFN-γ and TNF-α expression or release or lytic activity.

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