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Impact of the Multiple Sclerosis-Associated Genetic Variant Gly307Ser on Human CD8 T-Cell Functions

Abstract

Background And Objectives: The rs763361 nonsynonymous variant in the gene, which results in a glycine-to-serine substitution at position 307 of the CD226 protein, has been implicated as a risk factor of various immune-mediated diseases, including multiple sclerosis (MS). Compelling evidence suggests that this allele may play a significant role in predisposing individuals to MS by decreasing the immune-regulatory capacity of Treg cells and increasing the proinflammatory potential of effector CD4 T cells. However, the impact of this CD226 gene variant on CD8 T-cell functions, a population that also plays a key role in MS, remains to be determined.

Methods: To study whether the CD226 risk variant affects human CD8 T-cell functions, we used CD8 T cells isolated from peripheral blood mononuclear cell of 16 age-matched healthy donors homozygous for either the protective or the risk allele of CD226. We characterized these CD8 T cells on T-cell receptor (TCR) stimulation using high-parametric flow cytometry and bulk RNAseq and through characterization of canonical signaling pathways and cytokine production.

Results: On TCR engagement, the phenotype of ex vivo CD8 T cells bearing the protective (CD226-307Gly) or the risk (CD226-307Ser) allele of CD226 was largely overlapping. However, the transcriptomic signature of CD8 T cells from the donors carrying the risk allele presented an enrichment in TCR, JAK/STAT, and IFNγ signaling. We next found that the CD226-307Ser risk allele leads to a selective increase in the phosphorylation of the mitogen-activated protein kinases extracellular signal-regulated kinases 1 and 2 (ERK1/2) associated with enhanced phosphorylation of STAT4 and increased production of IFNγ.

Discussion: Our data suggest that the CD226-307Ser risk variant imposes immune dysregulation by increasing the pathways related to IFNγ signaling in CD8 T cells, thereby contributing to the risk of developing chronic inflammation.

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