The contribution of neutrophils to CNS autoimmunity.

Multiple sclerosis (MS) is believed to be initiated when myelin-specific T cells infiltrate the central nervous system (CNS), triggering subsequent recruitment of inflammatory leukocytes to the CNS. The contribution of neutrophils to CNS autoimmune disease has been underappreciated, but several studies in experimental autoimmune encephalomyelitis (EAE), an animal model of MS, indicate that neutrophils have an important role in inflammation. Neutrophils are hypothesized to contribute to the pathogenesis of EAE by producing cytokines and promoting breakdown of the blood brain barrier. Neutrophils may also influence the manifestation of EAE by facilitating parenchymal brain inflammation. This review summarizes evidence supporting a functional role for neutrophils in EAE and MS, highlighting the differential regulation of neutrophil recruitment in the brain and spinal cord.

GM-CSF is not essential for experimental autoimmune encephalomyelitis but promotes brain-targeted disease.

Experimental autoimmune encephalomyelitis (EAE) has been used as an animal model of multiple sclerosis to identify pathogenic cytokines that could be therapeutic targets. Granulocyte-macrophage colony-stimulating factor (GM-CSF) is the only cytokine reported to be essential for EAE. We investigated the role of GM-CSF in EAE in C3HeB/FeJ mice that uniquely exhibit extensive brain and spinal cord inflammation. Unexpectedly, GM-CSF-deficient C3HeB/FeJ mice were fully susceptible to EAE because IL-17 activity compensated for the loss of GM-CSF during induction of spinal cord-targeted disease. In contrast, both GM-CSF and IL-17 were needed to fully overcome the inhibitory influence of IFN-γ on the induction of inflammation in the brain. Both GM-CSF and IL-17 independently promoted neutrophil accumulation in the brain, which was essential for brain-targeted disease. These results identify a GM-CSF/IL-17/IFN-γ axis that regulates inflammation in the central nervous system and suggest that a combination of cytokine-neutralizing therapies may be needed to dampen central nervous system autoimmunity.

Distinct T cell signatures define subsets of patients with multiple sclerosis.

OBJECTIVE: We investigated T cell responses to myelin proteins in the blood of healthy controls and 2 groups of patients with relapsing-remitting multiple sclerosis (RRMS) who exhibited lesions either predominantly in the brain or predominantly in the spinal cord in order to assess whether distinct neuroinflammatory patterns were associated with different myelin protein-specific T cell effector function profiles and whether these profiles differed from healthy controls. METHODS: Peripheral blood mononuclear cells were obtained from patients with brain-predominant RRMS, patients with spinal cord-predominant RRMS, and age-matched healthy controls and analyzed by enzyme-linked immunosorbent spot assays to quantify interferon gamma-secreting (Th1) and interleukin 17-secreting (Th17) cells responding directly ex vivo to myelin basic protein (MBP) and myelin oligodendrocyte glycoprotein (MOG). RESULTS: Although MBP and MOG elicited different responses, patients with multiple sclerosis (MS) who had spinal cord-predominant lesions exhibited significantly higher Th17:Th1 ratios in response to both MBP and MOG compared to patients with brain-predominant MS. Incorporating the cytokine responses to both antigens into logistic regression models showed that these cytokine responses were able to provide good discrimination between patients with distinct neuroinflammatory patterns. CONCLUSIONS: Our findings suggest that the localization of lesions within the brain vs the spinal cord in patients with MS is associated with different effector T cell responses to myelin proteins. Further investigation of the relationship between T cell effector function, antigen specificities, and lesion sites may reveal features of pathogenic pathways that are distinct to patients with different neuroinflammatory patterns.

B cells promote induction of experimental autoimmune encephalomyelitis by facilitating reactivation of T cells in the central nervous system.

The efficacy of rituximab treatment in multiple sclerosis has renewed interest in the role of B cells in CNS autoimmunity. In this study, we show that B cells are the predominant MHC class II(+) subset in the naive CNS in mice, and they constitutively express proinflammatory cytokines. Incidence of experimental autoimmune encephalomyelitis induced by adoptive transfer was significantly reduced in C3HeB/Fej µMT (B cell-deficient) mice, suggesting an important role for CNS B cells in initiating inflammatory responses. Initial T cell infiltration of the CNS occurred normally in µMT mice; however, lack of production of T cell cytokines and other immune mediators indicated impaired T cell reactivation. Subsequent recruitment of immune cells from the periphery driven by this initial T cell reactivation did not occur in µMT mice. B cells required exogenous IL-1ß to reactivate Th17 but not Th1 cells in vitro. Similarly, reactivation of Th1 cells infiltrating the CNS was selectively impaired compared with Th17 cells in µMT mice, causing an increased Th17/Th1 ratio in the CNS at experimental autoimmune encephalomyelitis onset and enhanced brain inflammation. These studies reveal an important role for B cells within the CNS in reactivating T cells and influencing the clinical manifestation of disease.

Modeling the heterogeneity of multiple sclerosis in animals.

Multiple sclerosis (MS) is an inflammatory, demyelinating disease of the central nervous system (CNS) manifested with varying clinical course, pathology, and inflammatory patterns. There are multiple animal models that reflect different aspects of this heterogeneity. Collectively, these models reveal a balance between pathogenic and regulatory CD4(+) T cells, CD8(+) T cells, and B cells that influences the incidence, timing, and severity of CNS autoimmunity. In this review we discuss experimental autoimmune encephalomyelitis (EAE) models that have been used to study the pathogenic and regulatory roles of these immune cells; models that recapitulate different aspects of the disease seen in patients with MS, and questions remaining for future studies.