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Objective In multiple sclerosis ( MS), central nervous system ( CNS), cerebrospinal fluid ( CSF), and blood display TCR clonal expansions of CD8+ T cells. These clones have been assumed - but never demonstrated - to be similar in the three compartments. Addressing this key question is essential to infer the implication of peripheral clonally expanded CD8+ T cells in the disease. Methods For the first time, TCR V β repertoire from paired blood (purified CD8+ and CD4+ T cells), CSF and CNS (22 lesions, various inflammatory and demyelination statuses) samples from three MS patients was studied using complementary determining region 3 ( CDR3) spectratyping and high-throughput sequencing. In parallel, blood and CNS clonally expanded CD8+ T cells were characterized by fluorescent staining. Results TCR V β repertoire analysis revealed strong sharing of predominant T-cell clones between CNS lesions, CSF, and blood CD8+ T cells. In parallel, we showed that blood oligoclonal CD8+ T cells exhibit characteristics of pathogenic cells, as they displayed a bias toward a memory phenotype in MS patients, with increased expression of CCR5, CD11a and Granzyme B (GZM-B) compared to non oligoclonal counterparts. CNS-infiltrating T cells were mainly CD8 expressing CD11a and GZM-B. Interpretation This study highlights the predominant implication of CD8+ T cells in MS pathophysiology and demonstrates that potentially aggressive CD8+ T cells can be easily identified and characterized from blood and CSF samples. [ABSTRACT FROM AUTHOR]

Laser-capture microdissection (LCM) allows for retrieval of specific cell populations in situ. By combining immunofluorescent labeling with LCM, mRNAs can be probed by qRT-PCR for determining in situ gene expression during health and disease. This approach permits obtaining and analyzing histologically enriched cell populations in a tissue that can be hardly obtained from other methods such as white matter astrocytes from rodents or any individual cell population from archival human or rodent brain tissues. Herein, we present our methodology of laser-captured mouse spinal cord white matter astrocytes, which can be adapted for any cell type in CNS tissue and low RNAse containing tissues. The methods presented with an emphasis on tips and advices include the cryostat section preparation from snap-frozen tissue, an adapted immunofluorescent labeling, a brief overview of LCM using a UV-based technology with polyethylene membrane glass slides, procedures for direct use of RNA from lysis buffer vs. column-based purified RNA, RNA quality/quantity assessment, the reverse transcription and preamplification steps used before real-time qPCR analysis.