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MicroRNAs fine-tune the regulation of Th1/Th17 lymphocyte subsets in multiple sclerosis. We investigated the expression of miRNAs (previously associated with mycobacterial and viral infections) in MS patients and healthy donors (HD) following 6 months natalizumab therapy. In addition, Th1/Th17 cytokines and the presence of anti-EBNA1/VCA IgG in MS patients with different pattern of miRNA expression have been evaluated. MiR-155, miR-26a, miR-132, miR-146a and Th1/Th17 cytokines expression was detected by RT-real time PCR; moreover anti-EBNA1 and VCA IgG titres were measured by ELISA. We observed an up-regulation of miR-155 (p value = 0.009) and miR-132 (p value = 0.04) in MS patients compared to HD. In MS patients, IL-17a (p = 0.037), IFN γ (p = 0.012) and TNFα (p = 0.015) but not IL-6 were over-expressed compared to HD. Two different miRNAs patterns associated to the expression of different cytokines were observed in the MS cohort. Moreover, a down-regulation of miR-155 and miR-26a was seen in MS patients during and after natalizumab therapy. MS patients that over-expressed miR-155 showed a higher EBNA1 IgG titer than MS patients with high levels of miR-26a. In conclusions the expression of particular miRNAs modulates the pro-inflammatory cytokine expression and the humoral response against EBV and this expression is natalizumab regulated. [ABSTRACT FROM AUTHOR]