Systemic infections in multiple sclerosis and experimental autoimmune encephalomyelitis

Identifying the culprits in neurological autoimmune diseases

The target organ of neurological autoimmune diseases (NADs) is the central or peripheral nervous system. Multiple sclerosis (MS) is the most common NAD, whereas Guillain-Barré syndrome (GBS), myasthenia gravis (MG), and neuromyelitis optica (NMO) are less common NADs, but the incidence of these diseases has increased exponentially in the last few years. The identification of a specific culprit in NADs is challenging since a myriad of triggering factors interplay with each other to cause an autoimmune response. Among the factors that have been associated with NADs are genetic susceptibility, epigenetic mechanisms, and environmental factors such as infection, microbiota, vitamins, etc. This review focuses on the most studied culprits as well as the mechanisms used by these to trigger NADs.

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Neurological autoimmune diseases are caused by a complex interaction between genes, environmental factors, and epigenetic deregulation.

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Infectious agents can cause an autoimmune reaction to myelin epitopes through molecular mimicry and/or bystander activation.

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Gut microbiota dysbiosis contributes to neurological autoimmune diseases.

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Smoking increases the risk of NADs through inflammatory signaling pathways, oxidative stress, and Th17 differentiation.

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Deficiency in vitamin D favors NAD development through direct damage to the central and peripheral nervous system.

Peripheral Inflammation and Demyelinating Diseases

In recent decades, several neurodegenerative diseases have been shown to be exacerbated by systemic inflammatory processes. There is a wide range of literature that demonstrates a clear but complex relationship between the central nervous system (CNS) and the immunological system, both under naïve or pathological conditions. In diseased brains, peripheral inflammation can transform "primed" microglia into an "active" state, which can trigger stronger pathological responses. Demyelinating diseases are a group of neurodegenerative diseases characterized by inflammatory lesions associated with demyelination, which in turn induces axonal damage, neurodegeneration, and progressive loss of function. Among them, the most important are multiple sclerosis (MS) and neuromyelitis optica (NMO). In this review, we will analyze the effect of specific peripheral inflammatory stimuli in the progression of demyelinating diseases and discuss their animal models. In most cases, peripheral immune stimuli are exacerbating.

Disease-Specific Outcomes of Botulinum Toxin Injections for Neurogenic Detrusor Overactivity

Intradetrusor injection of botulinum toxin A (BTX-A) is an effective option for managing patients with neurogenic detrusor overactivity (NDO) who do not respond to or tolerate oral pharmacologic agents. There is level I evidence that intradetrusor injection of onabotulinumtoxinA for refractory NDO in patients with multiple sclerosis and spinal cord injury is associated with a significantly greater achievement of goals and improved performance in urodynamic studies than placebo. Pilot studies or small case series support BTX-A for NDO in patients with Parkinson's disease and cerebrovascular accident. BTX-A seems to be effective in children with myelomeningocele. However, no adult data exists.

Systemic Escherichia coli infection does not influence clinical symptoms and neurodegeneration in experimental autoimmune encephalomyelitis

Background

Systemic infections can influence the course of multiple sclerosis (MS), especially by driving recurrent acute episodes. The question whether the infection enhances tissue damage is of great clinical importance and cannot easily be assessed in clinical trials. Here, we investigated the effects of a systemic infection with Escherichia coli, a Gram-negative bacterium frequently causing urinary tract infections, on the clinical course as well as on neurodegeneration in experimental autoimmune encephalomyelitis (EAE), an animal model of MS.

Methods

Rats were immunized with myelin oligodendrocyte glycoprotein (MOG_1–125) and challenged intraperitoneally with live E. coli K1 in the preclinical or in the clinical phase of the disease. To ensure the survival of animals, antibiotic treatment with ceftriaxone was initiated 36 h after the infection and continued for 3 consecutive days.

Results

Systemic infection with E. coli did not influence the onset of clinical EAE symptoms or disease severity. Analysis of the optic nerve and retinal ganglion cells revealed no significant changes in the extent of inflammatory infiltrates, demyelination and neurodegeneration after E. coli infection.

Conclusions

We could not confirm the detrimental effect of lipopolysaccharide-induced systemic inflammation, a model frequently used to mimic the bacterial infection, previously observed in animal models of MS. Our results indicate that the effect of an acute E. coli infection on the course of MS is less pronounced than suspected and underline the need for adequate models to test the role of systemic infections in the pathogenesis of MS.

Role of pathogens in multiple sclerosis

Multiple sclerosis (MS) is an inflammatory demyelinating autoimmune disease of the central nervous system (CNS). Although the etiology of MS is unknown, genetic and environmental factors play a role. Infectious pathogens are the likely environmental factors involved in the development of MS. Pathogens associated with the development or exacerbation of MS include bacteria, such as Mycoplasma pneumoniae and Chlamydia pneumoniae, the Staphylococcus aureus-produced enterotoxins that function as superantigens, viruses of the herpes virus (Epstein-Barr virus and human herpesvirus 6) and human endogenous retrovirus (HERV) families and the protozoa Acanthamoeba castellanii. Evidence, from studies with humans and animal models, supporting the association of these various pathogens with the development and/or exacerbation of MS will be discussed along with the potential mechanisms including molecular mimicry, epitope spreading and bystander activation. In contrast, infection with certain parasites such as helminthes (Schistosoma mansoni, Fasciola hepatica, Hymenolepis nana, Trichuris trichiura, Ascaris lumbricoides, Strongyloides stercolaris, Enterobius vermicularis) appears to protect against the development or exacerbation of MS. Evidence supporting the ability of parasitic infections to protect against disease will be discussed along with a brief summary of a recent Phase I clinical trial testing the ability of Trichuris suis ova treatment to improve the clinical course of MS. A complex interaction between the CNS (including the blood-brain barrier), multiple infections with various infectious agents (occurring in the periphery or within the CNS), and the immune response to those various infections may have to be deciphered before the etiology of MS can be fully understood.

The diagnosis and management of lower urinary tract symptoms in multiple sclerosis patients

Sixty-five percent of multiple sclerosis patients have moderate to severe urinary symptoms and up to 14% initially present with urinary symptomatology. Urinary retention, neurogenic detrusor overactivity, and detrusor sphincter dyssynergia, all increase the risk for urinary tract infections in patients with multiple sclerosis, and these infections may exacerbate their immune response, leading to symptom progression. Fewer than half of the patients with urinary symptoms have seen a specialist and only half have been treated for their neurogenic detrusor overactivity. Several treatments including pelvic floor muscle therapy, pelvic floor electrical stimulation, anticholinergics, desmopressin, sacral nerve neuromodulation, posterior tibial nerve stimulation, cannabinoids, and intravesical therapy with vanniloids, as well as botulinum toxin, have all been shown to be effective in treating urinary symptoms in those with multiple sclerosis. Clean intermittent catheterization is invaluable in patients with persistent urinary retention to avoid infection and upper tract dysfunction. Indwelling transurethral catheterization should be avoided because of the high risk of infection. Identification and successful treatment of these urinary conditions will improve the health and quality of life for these men and women.

Contemporary management of the neurogenic bladder for multiple sclerosis patients

Urinary symptoms related to multiple sclerosis (MS) present a complex challenge for the treating physician. However, several treatment options are available for the symptomatic patient once the physician understands basic MS disease epidemiology and pathophysiology. Depending of disease status and symptoms, MS urinary symptoms may respond to directed behavioral, pharmacologic, intravesical, neuromodulation, or surgical therapies.

IDO upregulates regulatory T cells via tryptophan catabolite and suppresses encephalitogenic T cell responses in experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is a Th1 and Th17 cell-mediated autoimmune disease of the CNS. IDO and tryptophan metabolites have inhibitory effects on Th1 cells in EAE. For Th17 cells, IDO-mediated tryptophan deprivation and small molecule halofuginone-induced amino acid starvation response were shown to activate general control nonrepressed 2 (GCN2) kinase that directly or indirectly inhibits Th17 cell differentiation. However, it remains unclear whether IDO and tryptophan metabolites impact the Th17 cell response by mechanisms other than the GCN2 kinase pathway. In this article, we show that IDO-deficient mice develop exacerbated EAE with enhanced encephalitogenic Th1 and Th17 cell responses and reduced regulatory T cell (Treg) responses. Administration of the downstream tryptophan metabolite 3-hydroxyanthranillic acid (3-HAA) enhanced the percentage of Tregs, inhibited Th1 and Th17 cells, and ameliorated EAE. We further demonstrate that Th17 cells are less sensitive to direct suppression by 3-HAA than are Th1 cells. 3-HAA treatment in vitro reduced IL-6 production by activated spleen cells and increased expression of TGF-β in dendritic cells (DCs), which correlated with enhanced levels of Tregs, suggesting that 3-HAA-induced Tregs contribute to inhibition of Th17 cells. By using a DC-T cell coculture, we found that 3-HAA-treated DCs expressed higher levels of TGF-β and had properties to induce generation of Tregs from anti-CD3/anti-CD28-stimulated naive CD4(+) T cells. Thus, our data support the hypothesis that IDO induces the generation of Tregs via tryptophan metabolites, such as 3-HAA, which enhances TGF-β expression from DCs and promotes Treg differentiation.

Toll-like receptors in multiple sclerosis

Multiple sclerosis (MS) is a chronic disease of the central nervous system (CNS) characterized by inflammation, demyelination, and axonal pathology. The exact causes of MS are unknown, but environmental factors including pathogens are believed to contribute to the development of disease. Toll-like receptors (TLRs) are a family of receptors important in pathogen recognition and host defense. TLRs are expressed by a variety of peripheral immune cells as well as resident cells of the CNS. Studies indicate that TLRs play a significant role in modulating MS, as well as experimental autoimmune encephalomyelitis (EAE), an animal model of MS. This review will discuss the current understanding of the role of TLRs in modulating EAE and MS.