Altered susceptibility to EAE in congenic NOD mice: Altered processing of the encephalitogenic MOG35-55 peptide by NOR/LtJ mice

Thymus-specific serine protease, a protease that shapes the CD4 T cell repertoire

The lifespan of T cells is determined by continuous interactions of their T cell receptors (TCR) with self-peptide-MHC (self-pMHC) complexes presented by different subsets of antigen-presenting cells (APC). In the thymus, developing thymocytes are positively selected through recognition of self-pMHC presented by cortical thymic epithelial cells (cTEC). They are subsequently negatively selected by medullary thymic epithelial cells (mTEC) or thymic dendritic cells (DC) presenting self-pMHC complexes. In the periphery, the homeostasis of mature T cells is likewise controlled by the interaction of their TCR with self-pMHC complexes presented by lymph node stromal cells while they may be tolerized by DC presenting tissue-derived self-antigens. To perform these tasks, the different subsets of APC are equipped with distinct combination of antigen processing enzymes and consequently present specific repertoire of self-peptides. Here, we discuss one such antigen processing enzyme, the thymus-specific serine protease (TSSP), which is predominantly expressed by thymic stromal cells. In thymic DC and TEC, TSSP edits the repertoire of peptide presented by class II molecules and thus shapes the CD4 T cell repertoire.

Thymic-Specific Serine Protease Limits Central Tolerance and Exacerbates Experimental Autoimmune Encephalomyelitis

The genetic predisposition to multiple sclerosis (MS) is most strongly conveyed by MHC class II haplotypes, possibly by shaping the autoimmune CD4 T cell repertoire. Whether Ag-processing enzymes contribute to MS susceptibility by editing the peptide repertoire presented by these MHC haplotypes is unclear. Thymus-specific serine protease (TSSP) is expressed by thymic epithelial cells and thymic dendritic cells (DCs) and, in these two stromal compartments, TSSP edits the peptide repertoire presented by class II molecules. We show in this article that TSSP increases experimental autoimmune encephalomyelitis severity by limiting central tolerance to myelin oligodendrocyte glycoprotein. The effect on experimental autoimmune encephalomyelitis severity was MHC class II allele dependent, because the lack of TSSP expression conferred protection in NOD mice but not in C57BL/6 mice. Importantly, although human thymic DCs express TSSP, individuals segregate into two groups having a high or 10-fold lower level of expression. Therefore, the level of TSSP expression by thymic DCs may modify the risk factors for MS conferred by some MHC class II haplotypes.

The Non-Obese Diabetic Mouse Strain as a Model to Study CD8(+) T Cell Function in Relapsing and Progressive Multiple Sclerosis

Multiple sclerosis (MS) is a neurodegenerative disease resulting from an autoimmune attack on central nervous system (CNS) myelin. Although CD4⁺ T cell function in MS pathology has been extensively studied, there is also strong evidence that CD8⁺ T lymphocytes play a key role. Intriguingly, CD8⁺ T cells accumulate in great numbers in the CNS in progressive MS, a form of the disease that is refractory to current disease-modifying therapies that target the CD4⁺ T cell response. Here, we discuss the function of CD8⁺ T cells in experimental autoimmune encephalomyelitis (EAE), a mouse model of MS. In particular, we describe EAE in non-obese diabetic (NOD) background mice, which develop a pattern of disease characterized by multiple attacks and remissions followed by a progressively worsening phase. This is highly reminiscent of the pattern of disease observed in nearly half of MS patients. Particular attention is paid to a newly described transgenic mouse strain (1C6) on the NOD background whose CD4⁺ and CD8⁺ T cells are directed against the encephalitogenic peptide MOG_[35–55]. Use of this model will give us a more complete picture of the role(s) played by distinct T cell subsets in CNS autoimmunity.

Altered Th17/Treg balance and dysregulated IL-1β response influence susceptibility/resistance to experimental autoimmune arthritis

This study was aimed at gaining an insight into immune mechanisms of differential susceptibility to autoimmunity of individuals sharing the same major histocompatibility complex by studying arthritis-susceptible Lewis (LEW) and arthritis-resistant Wistar Kyoto (WKY) rats (both RT.1(l)) using the adjuvant arthritis (AA) model of rheumatoid arthritis (RA). Lymph node cells (LNC) and synovium-infiltrating cells (SIC) of LEW and WKY rat subjected to an arthritogenic challenge were tested. The frequency of T helper 17 (Th17) and T regulatory (Treg) cells was determined by flow cytometry, whereas serum and spleen adherent cell (SAC)-derived supernatant were analyzed for specific cytokines and chemokines. We observed that WKY rats are not deficient in generating a Th17 response to the arthritogenic challenge in LNC (periphery); however, the Th17/Treg ratio is markedly reduced in the joint (target organ) of WKY versus LEW rats because of reduced Th17 levels therein in WKY rats. These results suggest differential and selective decrease in Th17 cell migration into the joints of WKY rats. Interestingly, serum levels of chemokines RANTES and MCP-1 were reduced in WKY rats. Furthermore, WKY rats showed reduced serum IL-1β level in vivo but no defect in IL-1β production by SAC in vitro, suggesting an effective in vivo regulation of IL-1β response. We also unraveled the role of interferon-γ (IFNγ), which we have previously reported to be increased in WKY versus LEW rats, in regulation of IL-1β. Thus, reduced Th17/Treg ratio in the target organ (joints) and decreased systemic IL-1β might contribute to the AA-resistance of WKY rats; whereas the converse factors render LEW more vulnerable to AA.

Modelling MS: Chronic-Relapsing EAE in the NOD/Lt Mouse Strain

Modelling complex disorders presents considerable challenges, and multiple sclerosis (MS) is no exception to this rule. The aetiology of MS is unknown, and its pathophysiology is poorly understood. Moreover, the last two decades have witnessed a dramatic revision of the long-held view of MS as an inflammatory demyelinating white matter disease. Instead, it is now regarded as a global central nervous system (CNS) disorder with a neurodegenerative component. Currently, there is no animal model recapitulating MS immunopathogenesis. Available models are based on autoimmune-mediated demyelination, denoted experimental autoimmune encephalomyelitis (EAE) or virally or chemically induced demyelination. Of these, the EAE model has been the most commonly used. It has been extensively improved since its first description and now exists as a number of variants, including genetically modified and humanized versions. Nonetheless, EAE is a distinct disease, and each variant models only certain facets of MS. Whilst the search for more refined MS models must continue, it is important to further explore where mechanisms underlying EAE provide proof-of-principle for those driving MS pathogenesis. EAE variants generated with the myelin component myelin oligodendrocyte glycoprotein (MOG) have emerged as the preferred ones, because in this particular variant disease is associated with both T- and B-cell effector mechanisms, together with demyelination. MOG-induced EAE in the non-obese diabetic (NOD) mouse strain exhibits a chronic-relapsing EAE clinical profile and high disease incidence. We describe the generation of this variant, its contribution to the understanding of MS immune and pathogenetic mechanisms and potential for evaluation of candidate therapies.

T cell-specific BLIMP-1 deficiency exacerbates experimental autoimmune encephalomyelitis in nonobese diabetic mice by increasing Th1 and Th17 cells

Recently, we demonstrated that B lymphocyte-induced maturation protein 1 (BLIMP-1) has a role in regulating the differentiation and effector function of Th1 and Th17 cells. As these cells play critical roles in the induction and pathogenesis of experimental autoimmune encephalomyelitis (EAE), we investigated the potential role of T cell BLIMP-1 in modulating MOG35-55-induced EAE. We established T cell-specific BLIMP-1 conditional knockout (CKO) NOD mice to dissect the role of BLIMP-1 in EAE using loss-of-function model. Our results indicate that EAE severity is dramatically exacerbated in CKO mice. The numbers of CNS-infiltrating Th1, Th17, IFN-γ(+)IL-17A(+), and IL-21(+)IL-17A(+) CD4(+) T cells are remarkably increased in brain and spinal cord of CKO mice. Moreover, the ratio of Tregs/effectors and IL-10 production of Tregs are significantly downregulated in CNS of CKO mice. We conclude that BLIMP-1 suppresses autoimmune encephalomyelitis via downregulating Th1 and Th17 cells and impairing Treg cells.

Animal models of multiple sclerosis--potentials and limitations

Experimental autoimmune encephalomyelitis (EAE) is still the most widely accepted animal model of multiple sclerosis (MS). Different types of EAE have been developed in order to investigate pathogenetic, clinical and therapeutic aspects of the heterogenic human disease. Generally, investigations in EAE are more suitable for the analysis of immunogenetic elements (major histocompatibility complex restriction and candidate risk genes) and for the study of histopathological features (inflammation, demyelination and degeneration) of the disease than for screening of new treatments. Recent studies in new EAE models, especially in transgenic ones, have in connection with new analytical techniques such as microarray assays provided a deeper insight into the pathogenic cellular and molecular mechanisms of EAE and potentially of MS. For example, it was possible to better delineate the role of soluble pro-inflammatory (tumor necrosis factor-α, interferon-γ and interleukins 1, 12 and 23), anti-inflammatory (transforming growth factor-β and interleukins 4, 10, 27 and 35) and neurotrophic factors (ciliary neurotrophic factor and brain-derived neurotrophic factor). Also, the regulatory and effector functions of distinct immune cell subpopulations such as CD4+ Th1, Th2, Th3 and Th17 cells, CD4+FoxP3+ Treg cells, CD8+ Tc1 and Tc2, B cells and γδ+ T cells have been disclosed in more detail. The new insights may help to identify novel targets for the treatment of MS. However, translation of the experimental results into the clinical practice requires prudence and great caution.