Modeling a Complex Disease

Modeling a complex disease: Multiple sclerosis-Update 2020

Multiple sclerosis (MS) is a complex inflammatory disease of the central nervous system (CNS) with an unknown etiology. Thereby, MS is not a uniform disease but rather represents a spectrum of disorders, where each aspect needs to be modeled with specific requirements-for a systematic overview see our previous issue of this review (Kurschus, Wortge, & Waisman, 2011). However, there is broad consensus about the critical involvement of the immune system in the disease pathogenesis. To better understand how the immune system contributes to CNS autoimmunity, the model of experimental autoimmune encephalomyelitis (EAE) was developed. EAE can be induced in susceptible animals in many different ways, with the most popular protocol involving the activation of self-reactive T cells by a peptide based on the myelin oligodendrocyte glycoprotein sequence. In the last 10 years this model has led to major advances in our understanding of the immune system, especially the nature of IL-17-producing T cells (Th17 cells), host-microbiome interactions, the gut-brain axis and how the immune system can cause damage in different regions of the brain and the spinal cord. This update summarizes some of the main achievements in the field in the last 10 years.

EBI2 - Sensor for dihydroxycholesterol gradients in neuroinflammation

Dihydroxycholesterols such as 7α,25-dihydroxysterols (7α,25-OHC) and 7α,27-OHC are generated from cholesterol by the enzymes CH25H, CYP7B1 and CYP27A1 in steady state but also in the context of inflammation. The G-protein coupled receptor (GPCR) Epstein-Barr virus-induced gene 2 (EBI2), also known as GPR183, senses these oxysterols and induces chemotactic migration of immune cells towards higher concentrations of these ligands. We recently showed that these ligands are upregulated in the CNS in experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis and that EBI2 enhanced early infiltration of encephalitogenic T cells into the CNS. In this short-review we discuss the role of dihydroxysterol-sensing by immune cells in neuroinflammation.

TGF-β inhibitor Smad7 regulates dendritic cell-induced autoimmunity

TGF-β is an anti-inflammatory cytokine whose signaling is negatively controlled by Smad7. Previously, we established a role for Smad7 in the generation of autoreactive T cells; however, the function of Smad7 in dendritic cells (DCs) remains elusive. Here, we demonstrate that DC-specific Smad7 deficiency resulted in elevated expression of the transcription factors Batf3 and IRF8, leading to increased frequencies of CD8⁺CD103⁺ DCs in the spleen. Furthermore, Smad7-deficient DCs expressed higher levels of indoleamine 2,3-dioxygenase (IDO), an enzyme associated with tolerance induction. Mice devoid of Smad7 specifically in DCs are resistant to the development of experimental autoimmune encephalomyelitis (EAE) as a result of an increase of protective regulatory T cells (Tregs) and reduction of encephalitogenic effector T cells in the central nervous system. In agreement, inhibition of IDO activity or depletion of Tregs restored disease susceptibility. Intriguingly, when Smad7-deficient DCs also lacked the IFN-γ receptor, the mice regained susceptibility to EAE, demonstrating that IFN-γ signaling in DCs mediates their tolerogenic function. Our data indicate that Smad7 expression governs splenic DC subset differentiation and is critical for the promotion of their efficient function in immunity.

The Role of Latently Infected B Cells in CNS Autoimmunity

The onset of multiple sclerosis (MS) is caused by both genetic and environmental factors. Among the environmental factors, it is believed that previous infection with Epstein–Barr virus (EBV) may contribute in the development of MS. EBV has been associated with other autoimmune diseases, such as systemic lupus erythematous, and cancers like Burkitt’s lymphoma. EBV establishes a life-long latency in B cells with occasional reactivation of the virus throughout the individual’s life. The role played by B cells in MS pathology has been largely studied, yet is not clearly understood. In MS patients, Rituximab, a novel treatment that targets CD20⁺ B cells, has proven to have successful results in diminishing the number of relapses in remitting relapsing MS; however, the mechanism of how this drug acts has not been clearly established. In this review, we analyze the evidence of how B cells latently infected with EBV might be altering the immune system response and helping in the development of MS. We will also discuss how animal models, such as experimental autoimmune encephalomyelitis (EAE) and murine gammaherpesvirus-68 (γHV-68), can be used as powerful tools in the study of the relationship between EBV, MS, and B cells.

Helminth infections decrease host susceptibility to immune-mediated diseases

Helminthic infection has become rare in highly industrialized nations. Concurrent with the decline in helminthic infection has been an increase in the prevalence of inflammatory disease. Removal of helminths from our environment and their powerful effects on host immunity may have contributed to this increase. Several helminth species can abrogate disease in murine models of inflammatory bowel disease, type 1 diabetes, multiple sclerosis, and other conditions. Helminths evoke immune regulatory pathways often involving dendritic cells, regulatory T cells, and macrophages that help to control disease. Cytokines, such as IL-4, IL-10, and TGF-β, have a role. Notable is the helminthic modulatory effect on innate immunity, which impedes development of aberrant adaptive immunity. Investigators are identifying key helminth-derived immune modulatory molecules that may have therapeutic usefulness in the control of inflammatory disease.