Immunological mechanisms regulating neuroinflammation : a role for C-type lectin receptors and vitamin D

Abstract

Autoimmunity of the central nervous system (CNS) such as in Multiple Sclerosis (MS) or its animal model Experimental Autoimmune Encephalomyelitis (EAE) requires the activation of self-reactive immune cells and the presentation of self-antigen by mature antigen presenting cells (APCs). In this thesis I have studied genetic and environmental mechanisms affecting APCs and CD4+ T cells which regulate susceptibility to EAE induced with myelin oligodendrocyte glycoprotein (MOG) in the rat. Bone marrow derived dendritic cells (BMDCs) are frequently used as in vitro alternatives to APCs, particularly DCs observed in vivo. However it is crucial to discriminate which cell type is being generated as they will serve different functions.

In paper I, we have first phenotypically and functionally characterized different types of in vitro generated BMDCs with different protocols. We have shown that BMDCs generated with FMS-like tyrosine kinase 3 ligand (FL-BMDCs) shared gene expression and characteristics of classical DCs observed in the body. We also demonstrated that BMDCs generated with the cytokines GM-CSF and IL-4 (G4-BMDCs) were pro-inflammatory and resembled monocytes derived DCs (MCs) generated in vivo under inflammatory conditions. In the EAE model, APCs are crucial for the priming of CD4+ T cells in the draining lymph nodes following immunization, as well as their reactivation in the CNS prior to disease onset. In paper II, we have characterized how two c-type lectin receptors (CLRs), MCL and Mincle, conferred susceptibility to EAE by directing the re-activation of CD4+ T cells in the CNS towards the pathogenic IL-17-producing T helper (Th17) phenotype. We showed that this was in part due to the alarmin SAP130, an endogenous ligand of MCL and Mincle. Furthermore, we determined that the MCL/MINCLE signaling pathway was hyperactive in MS blood monocytes and might contribute to disease severity. Many environmental factors have been linked to increased risk of developing MS including lack of sun exposure and vitamin D deficiency. In paper III, we described how vitamin D affects the activation of CD4+ T cells via epigenetic mechanisms (miRNA, DNA methylation and histone modification) resulting in a reduction of their pathogenic potential.

This thesis showed, using different approaches in rodent models and human material, how genetic and environmental factors relevant for MS could regulate susceptibility to EAE by modulating the development of pathogenic Th17 cells. In paper I, we characterized BMDCs routinely used in vitro to study immune functions of myeloid cells. In paper II and paper III, we addressed two distinct mechanisms regulating T cell activation and EAE development. This work presented integrative strategies to address biological questions and provided novel insight into the immunological aspects of autoimmune neuroinflammation.