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Background and purpose Natural killer (NK) cells may play a role in multiple sclerosis (MS). Ratios of NK cells to CD4+ T cells have been proposed as a biomarker for the therapeutic effect of stem cell transplantation in MS. The objectives here were to explore the relevance of this ratio in MS patients by analysing NK and T cell subsets, as well as their prognostic value for disease activity. Methods Baseline peripheral blood mononuclear cells of 50 relapsing–remitting MS patients, participating in our vitamin D supplementation study (SOLARIUM), were analysed with flow cytometry. Disease activity was measured as new magnetic resonance imaging lesions, relapses and mean plasma neurofilament light chain levels after 48 weeks of follow‐up. Results The proportion of NK cells correlated negatively with CD4+ T cells (R = −0.335, p = 0.001) and interleukin 17A (IL‐17A+) CD4+ T cells (R = −0.203, p = 0.043). Participants with magnetic resonance imaging activity or relapses displayed lower NK/IL‐17A+ CD4+ T cell ratios (p =0.025 and p = 0.006, respectively). The NK/IL‐17A+ CD4+ T cell ratio correlated negatively with neurofilament light chain levels (R = −0.320, p = 0.050). Vitamin D supplementation did not affect these ratios. Conclusions Our data suggest a protective role of an expanded NK cell compartment compared to the CD4+ T cell subset fractions in relapsing–remitting MS patients. NK/CD4+ T cell ratios may be a prognostic biomarker for disease activity in MS.

NK/T-cell ratios predict disease activity in relapsing remitting multiple sclerosis (RRMS). We investigated in 50 RRMS patients whether interleukin-2 receptor alpha-chain (IL-2Rα) expression and shedding associates with NK/ T-cell balance, as suggested by daclizumab-trials in RRMS. A subsample (N = 31) was genotyped for IL2RAassociated MS risk SNPs. CD56 bright NK-cell/IL-17A + CD4 + T-cell ratios correlated negatively with plasma and PBMC-culture supernatant sIL-2Rα-levels [R =-0.209; p = 0.038 and R =-0.254; p = 0.012, resp.], and with CD4 + T-cell CD25 MFI [R =-0.341; p = 0.001]. Carriers of the rs3118470 risk-allele showed higher sIL-2Rαlevels (P = 0.031) and a lower CD56 bright NK-cell/IL-17A + CD4 + T-cell ratio (P = 0.038). Therefore, IL-2Rα may be involved in the interplay between NK-cells and T-cells.

Introduction A poor 25-hydroxyvitamin D (25(OH)D) status is a much replicated risk factor for developing multiple sclerosis (MS), and several vitamin D-associated single nucleotide polymorphisms (SNPs) have been associated with a higher risk of MS. However, studies on the benefit of vitamin D supplementation in MS show inconclusive results. Here, we explore whether vitamin D-associated SNPs and MS risk alleles confound serological response to vitamin D supplementation. Methods 34 participants from the SOLARIUM study consented to genotyping, of which 26 had vitamin D data available. The SOLARIUM study randomised relapsing-remitting MS patients to placebo or 14,000 IU vitamin D3 for 48 weeks. Participants were categorised as either ‘carriers’ or ‘non-carriers’ of the risk allele for 4 SNPs: two related to D binding protein (DBP) and associated with lower 25(OH)D levels (rs4588 and rs7041), and two related to vitamin D metabolism enzymes CYP27B1 and CYP24A1 and associated with a higher risk of MS (rs12368653; rs2248359, respectively). 25(OH)D levels were determined at baseline and after 48 weeks. Results The DBP-related SNPs showed no difference in 25(OH)D status at baseline, but carriers of the rs7041 risk allele showed lower 25(OH)D-levels compared to non-carriers after 48 weeks of supplementation (median 224.2 vs. 332.0 nmol/L, p = 0.013). For CYP related SNPs, neither showed a difference at baseline, but carriers of the rs12368653 risk allele showed higher 25(OH)D-levels compared to non-carriers after 48 weeks of supplementation (median 304.1 vs. 152.0 nmol/L, p = 0.014). Discussion Vitamin D-related SNPs affect the serological response to high-dose vitamin D supplementation. The effects on more common doses of vitamin D, as well as the clinical consequence of this altered response, need to be investigated further.

The development, progression, diagnosis and treatment of autoimmune diseases, such as multiple sclerosis (MS), are convoluted processes which remain incompletely understood. Multiple studies demonstrated that the interleukin (IL)-2 – IL-2 receptor (IL-2R) pathway plays a pivotal role within these processes. The most striking functions of the IL-2 – IL-2R pathway are the differential induction of autoimmune responses and tolerance. This paradoxical function of the IL-2 – IL-2R pathway may be an attractive therapeutic target for autoimmune diseases such as MS. However, the exact mechanisms that lead to autoimmunity or tolerance remain to be elucidated. Furthermore, another factor of this pathway, the soluble form of the IL-2R (sIL-2R), further complicates understanding the role of the IL-2 – IL-2R pathway in MS. The challenge is to unravel these mechanisms to prevent, diagnose and recover MS. In this review, first, the current knowledge of MS and the IL-2 – IL-2R pathway are summarized. Second, the key findings of the relation between the IL-2 – IL-2R pathway and MS have been highlighted. Eventually, this review may launch broad interest in the IL-2 – IL-2R pathway propelling further research in autoimmune diseases, including MS.

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