Gurumoorthy Krishnamoorthy

Commensal microbiota and myelin autoantigen cooperate to trigger autoimmune demyelination

Active multiple sclerosis lesions show inflammatory changes suggestive of a combined attack by autoreactive T and B lymphocytes against brain white matter. These pathogenic immune cells derive from progenitors that are normal, innocuous components of the healthy immune repertoire but become autoaggressive upon pathological activation. The stimuli triggering this autoimmune conversion have been commonly attributed to environmental factors, in particular microbial infection. However, using the relapsing–remitting mouse model of spontaneously developing experimental autoimmune encephalomyelitis, here we show that the commensal gut flora—in the absence of pathogenic agents—is essential in triggering immune processes, leading to a relapsing–remitting autoimmune disease driven by myelin-specific CD4+ T cells. We show further that recruitment and activation of autoantibody-producing B cells from the endogenous immune repertoire depends on availability of the target autoantigen, myelin oligodendrocyte glycoprotein (MOG), and commensal microbiota. Our observations identify a sequence of events triggering organ-specific autoimmune disease and these processes may offer novel therapeutic targets.

Selective transfer of exosomes from oligodendrocytes to microglia by macropinocytosis

The transfer of antigens from oligodendrocytes to immune cells has been implicated in the pathogenesis of autoimmune diseases. Here, we show that oligodendrocytes secrete small membrane vesicles called exosomes, which are specifically and efficiently taken up by microglia both in vitro and in vivo. Internalisation of exosomes occurs by a macropinocytotic mechanism without inducing a concomitant inflammatory response. After stimulation of microglia with interferon-γ, we observe an upregulation of MHC class II in a subpopulation of microglia. However, exosomes are preferentially internalised in microglia that do not seem to have antigen-presenting capacity. We propose that the constitutive macropinocytotic clearance of exosomes by a subset of microglia represents an important mechanism through which microglia participate in the degradation of oligodendroglial membrane in an immunologically ‘silent’ manner. By designating the capacity for macropinocytosis and antigen presentation to distinct cells, degradation and immune function might be assigned to different subtypes of microglia.

Spontaneous opticospinal encephalomyelitis in a double-transgenic mouse model of autoimmune T cell/B cell cooperation

We describe a double-transgenic mouse strain (opticospinal EAE [OSE] mouse) that spontaneously develops an EAE-like neurological syndrome closely resembling a human variant of multiple sclerosis, Devic disease (also called neuromyelitis optica). Like in Devic disease, the inflammatory, demyelinating lesions were located in the optic nerve and spinal cord, sparing brain and cerebellum, and the murine lesions showed histological similarity with their human correlates. OSE mice have recombination-competent immune cells expressing a TCR-alphabeta specific for myelin oligodendrocyte glycoprotein (MOG) aa 35-55 peptide in the context of I-Ab along with an Ig J region replaced by the recombined heavy chain of a monoclonal antibody binding to a conformational epitope on MOG. OSE mouse B cells bound even high dilutions of recombinant MOG, but not MOG peptide, and processed and presented it to autologous T cells. In addition, in OSE mice, but not in single-transgenic parental mice, anti-MOG antibodies were switched from IgM to IgG1.

Spontaneous relapsing-remitting EAE in the SJL/J mouse: MOG-reactive transgenic T cells recruit endogenous MOG-specific B cells

We describe new T cell receptor (TCR) transgenic mice (relapsing-remitting [RR] mice) carrying a TCR specific for myelin oligodendrocyte glycoprotein (MOG) peptide 92–106 in the context of I-As. Backcrossed to the SJL/J background, most RR mice spontaneously develop RR experimental autoimmune encephalomyelitis (EAE) with episodes often altering between different central nervous system tissues like the cerebellum, optic nerve, and spinal cord. Development of spontaneous EAE depends on the presence of an intact B cell compartment and on the expression of MOG autoantigen. There is no spontaneous EAE development in B cell–depleted mice or in transgenic mice lacking MOG. Transgenic T cells seem to expand MOG autoreactive B cells from the endogenous repertoire. The expanded autoreactive B cells produce autoantibodies binding to a conformational epitope on the native MOG protein while ignoring the T cell target peptide. The secreted autoantibodies are pathogenic, enhancing demyelinating EAE episodes. RR mice constitute the first spontaneous animal model for the most common form of multiple sclerosis (MS), RR MS.

Functional and Pathogenic Differences of Th1 and Th17 Cells in Experimental Autoimmune Encephalomyelitis

Background There is consensus that experimental autoimmune encephalomyelitis (EAE) can be mediated by myelin specific T cells of Th1 as well as of Th17 phenotype, but the contribution of either subset to the pathogenic process has remained controversial. In this report, we compare functional differences and pathogenic potential of “monoclonal” T cell lines that recognize myelin oligodendrocyte glycoprotein (MOG) with the same transgenic TCR but are distinguished by an IFN-γ producing Th1-like and IL-17 producing Th17-like cytokine signature. Methods and Findings CD4+ T cell lines were derived from the transgenic mouse strain 2D2, which expresses a TCR recognizing MOG peptide 35–55 in the context of I-Ab. Adoptive transfer of Th1 cells into lymphopenic (Rag2−/−) recipients, predominantly induced “classic” paralytic EAE, whereas Th17 cells mediated “atypical” ataxic EAE in approximately 50% of the recipient animals. Combination of Th1 and Th17 cells potentiated the encephalitogenicity inducing classical EAE exclusively. Th1 and Th17 mediated EAE lesions differed in their composition but not in their localization within the CNS. While Th1 lesions contained IFN-γ, but no IL-17 producing T cells, the T cells in Th17 lesions showed plasticity, substantially converting to IFN-γ producing Th1-like cells. Th1 and Th17 cells differed drastically by their lytic potential. Th1 but not Th17 cells lysed autoantigen presenting astrocytes and fibroblasts in vitro in a contact-dependent manner. In contrast, Th17 cells acquired cytotoxic potential only after antigenic stimulation and conversion to IFN-γ producing Th1 phenotype. Conclusions Our data demonstrate that both Th1 and Th17 lineages possess the ability to induce CNS autoimmunity but can function with complementary as well as differential pathogenic mechanisms. We propose that Th17-like cells producing IL-17 are required for the generation of atypical EAE whereas IFN-γ producing Th1 cells induce classical EAE.

Myelin-specific T cells also recognize neuronal autoantigen in a transgenic mouse model of multiple sclerosis

We describe here the paradoxical development of spontaneous experimental autoimmune encephalomyelitis (EAE) in transgenic mice expressing a myelin oligodendrocyte glycoprotein (MOG)-specific T cell antigen receptor (TCR) in the absence of MOG. We report that in Mog-deficient mice (Mog−/−), the autoimmune response by transgenic T cells is redirected to a neuronal cytoskeletal self antigen, neurofilament-M (NF-M). Although components of radically different protein classes, the cross-reacting major histocompatibility complex I-Ab–restricted epitope sequences of MOG35–55 and NF-M18–30 share essential TCR contact positions. This pattern of cross-reaction is not specific to the transgenic TCR but is also commonly seen in MOG35–55–I-Ab–reactive T cells. We propose that in the C57BL/6 mouse, MOG and NF-M response components add up to overcome the general resistance of this strain to experimental induction of autoimmunity. Similar cumulative responses against more than one autoantigen may have a role in spontaneously developing human autoimmune diseases.

EAE: An immunologist's magic eye

EAE comes in many shapes and colors. Individual variants of EAE present a baffling complexity of different aspects and traits, clinical, immunological, and structural. But, embedded in this seemingly chaotic image, the educated eye will discern patterns that retrace fundamental features of immune response, in particular, autoimmunity and self‐tolerance. EAE and its variants thus can be likened to an autostereogram, i.e. they are an immunologists magic eye.

From classic to spontaneous and humanized models of multiple sclerosis: impact on understanding pathogenesis and drug development.

Multiple sclerosis (MS), a demyelinating disease of the central nervous system (CNS), presents as a complex disease with variable clinical and pathological manifestations, involving different pathogenic pathways. Animal models, particularly experimental autoimmune encephalomyelitis (EAE), have been key to deciphering the pathophysiology of MS, although no single model can recapitulate the complexity and diversity of MS, or can, to date, integrate the diverse pathogenic pathways. Since the first EAE model was introduced decades ago, multiple classic (induced), spontaneous, and humanized EAE models have been developed, each recapitulating particular aspects of MS pathogenesis. The advances in technologies of genetic ablation and transgenesis in mice of C57BL/6J background and the development of myelin-oligodendrocyte glycoprotein (MOG)-induced EAE in C57BL/6J mice yielded several spontaneous and humanized EAE models, and resulted in a plethora of EAE models in which the role of specific genes or cell populations could be precisely interrogated, towards modeling specific pathways of MS pathogenesis/regulation in MS. Collectively, the numerous studies on the different EAE models contributed immensely to our basic understanding of cellular and molecular pathways in MS pathogenesis as well as to the development of therapeutic agents: several drugs available today as disease modifying treatments were developed from direct studies on EAE models, and many others were tested or validated in EAE. In this review, we discuss the contribution of major classic, spontaneous, and humanized EAE models to our understanding of MS pathophysiology and to insights leading to devising current and future therapies for this disease.

Neutrophil-related factors as biomarkers in EAE and MS

Using a mouse model of multiple sclerosis (MS), the authors show that neutrophils expand in the bone marrow and accumulate in the circulation before clinical onset of disease. Early in disease development, neutrophils infiltrate the CNS, which is suppressed by G-CSF receptor deficiency and blockade of CXCL1 to ameliorate disease. In patients with MS, systemic expression of neutrophil-related mediators correlates with new lesion formation, lesion burden, and clinical disability.

Gut microbiota from multiple sclerosis patients enables spontaneous autoimmune encephalomyelitis in mice

Significance Studies using experimental models have indicated that multiple sclerosis (MS)-like disease can be triggered in the gut following interactions of brain autoimmune T lymphocytes with local microbiota. Here we studied the gut microbiota from monozygotic human twin pairs discordant for multiple sclerosis. When we transferred human-derived microbiota into transgenic mice expressing a myelin autoantigen-specific T cell receptor, we found that gut microbiota from multiple sclerosis-affected twins induced CNS-specific autoimmunity at a higher incidence than microbiota from healthy co-twins. Our results offer functional evidence that human microbiome components contribute to CNS-specific autoimmunity. There is emerging evidence that the commensal microbiota has a role in the pathogenesis of multiple sclerosis (MS), a putative autoimmune disease of the CNS. Here, we compared the gut microbial composition of 34 monozygotic twin pairs discordant for MS. While there were no major differences in the overall microbial profiles, we found a significant increase in some taxa such as Akkermansia in untreated MS twins. Furthermore, most notably, when transplanted to a transgenic mouse model of spontaneous brain autoimmunity, MS twin-derived microbiota induced a significantly higher incidence of autoimmunity than the healthy twin-derived microbiota. The microbial profiles of the colonized mice showed a high intraindividual and remarkable temporal stability with several differences, including Sutterella, an organism shown to induce a protective immunoregulatory profile in vitro. Immune cells from mouse recipients of MS-twin samples produced less IL-10 than immune cells from mice colonized with healthy-twin samples. IL-10 may have a regulatory role in spontaneous CNS autoimmunity, as neutralization of the cytokine in mice colonized with healthy-twin fecal samples increased disease incidence. These findings provide evidence that MS-derived microbiota contain factors that precipitate an MS-like autoimmune disease in a transgenic mouse model. They hence encourage the detailed search for protective and pathogenic microbial components in human MS.