Multiple sclerosis (MS) is an inflammatory disease of the CNS influenced by a combination of genetic predisposition and environmental factors. Vitamin D (VitD) deficiency is considered a major risk factor for MS. While VitD is associated with immunomodulatory roles, the exact mechanisms by which VitD protects from disease are still largely unknown. CD4 T cells play a key role in MS pathogenesis with autoimmune effector T cells (Teff) infiltrating the CNS across the blood-brain barrier (BBB) and regulatory T cells (Treg) displaying impaired functions. Here we show that treatment of human CD4 T cells with the active form of VitD (1,25-Dihydroxyvitamin D3; 1,25(OH)2D3) decreased cell-surface expression of α4β1- and αLβ2-integrins on Teff but not Treg and reduced Teff adhesion to their endothelial ligands VCAM-1 and ICAM-1. By employing live cell imaging, we observed that VitD treatment reduced arrest of Teff but not Treg to the BBB as well as ICAM-1 and VCAM-1 under physiological flow in vitro and differentially affected post-arrest behaviour of Teff versus Treg on the BBB under physiological flow. Furthermore, VitD treatment favoured the migration of Treg over Teff across the BBB under static and flow conditions in vitro. In vivo live cell imaging showed that VitD reduced T cell arrest on the inflamed BBB during autoimmune neuroinflammation. Finally, VitD also reduced expression of integrins mediating CNS homing on pathogenic CD4 T cells isolated from the CSF of persons with MS (PwMS). As VitD treatment did not alter barrier properties or adhesion molecule profile of our BBB model we propose a beneficial effect of VitD supplementation in PwMS by reducing CNS trafficking of pro-inflammatory T cells while leaving CNS entry of Treg unaffected. ### Competing Interest Statement The authors have declared no competing interest. Swiss National Science Foundation, 310030E_189312, CRSII3_154483 Swiss MS Society European Research Council, ERC-2013-ADG 340733 Agence Nationale de la Recherche, ANR-19-CE14-0043 Foundation France SEP Multiple Sclerosis Society, 859/07, 41 Eugène Devic EDMUS Foundation Fondation d'Aide pour la Recherche sur la Sclerose en Plaques Hubert Curien/germaine de Stael Bangerter Rhyner Foundation Edinburgh Neuroscience funds Uehara Memorial Foundation, https://ror.org/00gc20a07 European Committee for Treatment and Research in Multiple Sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS), in which T-cell migration into the CNS is key for pathogenesis. Patients with MS exhibit impaired regulatory T cell populations, and both Foxp3+ Tregs and type I regulatory T cells (Tr1) are dysfunctional. MS is a multifactorial disease and vitamin D deficiency is associated with disease. Herein, we examined the impact of 1,25(OH)2D3 on CD4+ T cells coactivated by either CD28 to induce polyclonal activation or by the complement regulator CD46 to promote Tr1 differentiation. Addition of 1,25(OH)2D3 led to a differential expression of adhesion molecules on CD28- and CD46-costimulated T cells isolated from both healthy donors or from patients with MS. 1,25(OH)2D3 favored Tr1 motility though a Vitamin D-CD46 crosstalk highlighted by increased VDR expression as well as increased CYP24A1 and miR-9 in CD46-costimulated T cells. Furthermore, analysis of CD46 expression on T cells from a cohort of patients with MS supplemented by vitamin D showed a negative correlation with the levels of circulating vitamin D. Moreover, t-Distributed Stochastic Neighbor Embedding (t-SNE) analysis allowed the visualization and identification of clusters increased by vitamin D supplementation, but not by placebo, that exhibited similar adhesion phenotype to what was observed in vitro. Overall, our data show a crosstalk between vitamin D and CD46 that allows a preferential effect of Vitamin D on Tr1 cells, providing novel key insights into the role of an important modifiable environmental factor in MS.

Praziquantel (PZQ) is an anthelminthic human and veterinary drug used to treat trematode and cestode worms. Changes in immune responses have been demonstrated in humans following curative PZQ treatment of schistosome infections. These changes have been attributed to the removal of immunosupressive worms and immune responses to parasite antigens exposed from dying worms. To date, there has been no study investigating the potential direct effect of PZQ on the host immune cells. Herein, we analyzed the effect of PZQ on human CD4 + T cells classically costimulated by CD3/CD28 or costimulated by the complement regulator CD46 to induce Type 1 regulatory T cells (Tr1). Our results show that PZQ enhanced T-cell proliferation, increased secretion of IL-17 and IL-10 but had no effect on secretion of GM-CSF or IFNγ. Moreover, PZQ increased the coexpression of CD49b and LAG-3, a hallmark of Tr1 cells, suggesting increased Tr1 differentiation. Indeed, supernatants from PZQ-treated cells were able to decrease bystander T-cell activation, and this was partly reduced when blocking IL-10. Hence, our study demonstrates that PZQ directly modulates human T-cell activation and promotes Tr1 differentiation, suggesting that PZQ may have immunomodulatory functions in parasite-unrelated human inflammatory diseases.

Praziquantel (PZQ) is an anthelminthic human and veterinary drug used to treat trematode and cestode worms. Changes in immune responses have been demonstrated in humans following curative PZQ treatment of schistosome infections. These changes have been attributed to the removal of immunosupressive worms and immune responses to parasite antigens exposed from dying worms. To date, there has been no study investigating the potential direct effect of PZQ on the host immune cells. Herein, we analyzed the effect of PZQ on human CD4+ T cells classically costimulated by CD3/CD28 or costimulated by the complement regulator CD46 to induce Type 1 regulatory T cells (Tr1). Our results show that PZQ enhanced T‐cell proliferation, increased secretion of IL‐17 and IL‐10 but had no effect on secretion of GM‐CSF or IFNγ. Moreover, PZQ increased the coexpression of CD49b and LAG‐3, a hallmark of Tr1 cells, suggesting increased Tr1 differentiation. Indeed, supernatants from PZQ‐treated cells were able to decrease bystander T‐cell activation, and this was partly reduced when blocking IL‐10. Hence, our study demonstrates that PZQ directly modulates human T‐cell activation and promotes Tr1 differentiation, suggesting that PZQ may have immunomodulatory functions in parasite‐unrelated human inflammatory diseases.

The complement system is an ancient and evolutionarily conserved effector system comprising in mammals over 50 circulating and membrane bound proteins. Complement has long been described as belonging to the innate immune system; however, a number of recent studies have demonstrated its key role in the modulation of the adaptive immune response. This review does not set out to be an exhaustive list of the numerous interactions of the many complement components with adaptive immunity; rather, we will focus more precisely on the role of some complement molecules in the regulation of antigen presenting cells, as well as on their direct effect on the activation of the core adaptive immune cells, B and T lymphocytes. Recent reports on the local production and activation of complement proteins also suggest a major role in the control of effector responses. The crucial role of complement in adaptive immunity is further highlighted by several examples of dysregulation of these pathways in human diseases.