Can a virus stabilize Multiple Sclerosis?

Multiple Sclerosis (MS) is a neurodegenerative disease in which the neurons in the central nervous system (CNS; brain and spinal cord) cannot communicate effectively. The root of the disease is the degradation of the sheath of fat that surrounds some CNS neurons (myelin) - thus disrupting the effectiveness with which the neurons can survive and signal to each other. This destruction of the neurons is largely thought to be a result of the body attacking itself (an autoimmune disease), and not originating from an outside bacteria or virus; this hypothesis is largely the result of mice models that show that injecting components of this myelin sheath into a mouse will make the mouse exhibit MS-like symptoms.

Ref: http://health.howstuffworks.com/diseases-conditions/musculoskeletal/multiple-sclerosis1.htm

Although it seems as if this disease's cause is well-known and can be modeled well in animals, effective therapies to MS have proven hard to develop - one reason for this is that MS is different in almost every patient as to when it is symptomatic or not. This variation is so great that MS is characterized into many types of the disease such as relapse-remitting MS (RRMS) which the patient experiences many symptoms for months and then relapses into a largely symptom free condition, only to repeat in the future. Further, secondary progressing MS (SPMS) is a type of the disease - when symptomatic - declines at a devastating rate. There are more types, such as some that do not relapse and a continual decline is observed. It has been hypothesized that the Epstein-Barr virus (EBV; commonly known to cause mononucleosis) has some influence on this stability of disease - although results have not been very conclusive. This variability in the disease, as you can assume, confounds scientists researching therapies and potential cures to this devastating disease.

In hopes of elucidating why this variability is so great in this disease and if EPV has a role in disease stability, Annunziata et al in Italy investigated the role of EPV-positive B cells in disease severity. By extracting B cells from patients with MS, they examined the spectrum of antibodies that were produced by the MS patients of varying disease type. Initially, they identified 7 monoclonal antibodies (mAbs) that were found to bind a specific epitope (105-120) in one of the components of myelin that surround the neurons, MBP (myelin-basic protein). They chose this epitope of MBP because these mAbs were detected in the more 'stable' MS patients - and hoped to find something unique in these patients' body responses to the disease. Further testing included myelin-reactive T cells from MS to be evaluated in environments of the mAbs. Interestingly enough, only 3 mAbs showed dose-dependent inhibitory effects to the T cells - which are thought to contribute to the damaging environment in MS.

Transglutaminase-2 and Celiac Disease

Celiac disease is an autoimmune disease that has become increasingly prevalent in recent years.   It is an immune reaction that occurs with gluten, which is a protein found in wheat, barley, and malt.  This reaction causes inflammation, which damages the small intestine.  You may be thinking that wheat, malt, and barley are in everything!  So, what do people who suffer from celiac eat?  As someone who suffers from celiac, I can tell you the transition to a gluten free diet wasn’t easy, but luckily there are a lot of good, gluten free alternatives that have been developed.  Even though celiac can be helped with dietary accommodation, it is still important to try to understand what is causes the autoimmune response in order to potentially develop a treatment for celiac disease someday.  Unfortunately, it is not well understood how the autoreactive B cells become activated in celiac, but it is known that celiac disease is associated with autoantibodies produced that are specific for the transglutaminase-2 (TG2) enzyme.  In the paper Transglutaminase 2-Specific Autoantibodies in Celiac Disease Target Clustered, N-Terminal Epitopes Not Displayed on the Surface of Cells, the authors Iversen et al. investigated the mechanism that controls the formation of the TG2 autoantibodies.

Transglutaminase-2 is an enzyme that is involved in the deamination of glutamine residues, during them into glutamic acid.  This process increases their affinity for the HLA molecules associated with the disease, thus increasing the reactivity of gluten.  The anti-TG2 autoantibodies are an important marker of celiac disease, but it is unknown how these autoantibodies are contributing the disease.  In the lab’s previous research, they have identified various monoclonal (target 1 particular antigen) TG2-reactive antibodies (mAbs), and they have found that the antibodies target distinct (but close or overlapping) regions.  They define these regions as epitopes 1-4 throughout the paper. 

           

In order to determine the specificity of the mAbs, they stained the small intestinal tissue sections with immunofluorescent dye in either wild-type or mice deficient in TG2.  There was only fluorescence (indicating mAb binding) in the tissues containing TG2, which suggests that the mAbs are highly specific to TG2.  They also attempted to determine whether the mAbs would react with other members of the transglutaminase family, TG3 and TG6, which have also been associated with celiac disease.  They did not find any reactivity, which indicated that autoantibodies against other transglutaminases in celiac disease are created in dependently than the anti-TG2 autoantibodies.

TG2 has both an open and closed conformation.  It was thought that the epitopes on TG2 targeted by the autoantibodies were conformational, it would be expected that the mAbs would differ in binding strength to the two conformations.  Using an ELISA assay, the authors used the natural conformational regulators of TG2, Ca²⁺ (open conformation) and GTP (closed conformation) to measure the binding strength of the mAbs in each of the conformations.  The binding affinity of the mAbs was increased by Ca²⁺, but decreased by GTP.  This suggests that in celiac disease the open conformation of TG2 is the one that is targeted by the autoantibodies.

In a recent study done by Simon-Vecsei et al. , they identified an epitope targeted by celiac disease serum autoantibodies.  The authors wanted to know if their mAbs would react with the newly discovered epitope.  They constructed a triple mutation in the epitope and measured the binding strength with the mAbs by ELISA.  These mutations resulted in loss in reactivity for the mAbs in the epitope 2 group and the epitope 3 group.  This suggests that while this epitope is one of the major targets of autoantibodies in celiac disease, it is not the only one since the mAbs in the epitope 1 and 4 groups do not interact with it. 

SLAM Associated Protein (SAP) may Provide a Critical Role for Autoimmune Collagen Induced Arthritis through T Cell Development

             The formation of immune cells which attack one's own body (known collectively as autoimmune diseases) is still a widely studied topic which has yet to be fully understood. In normal immune function adaptive immune cells such as B cells and T cells are screened during development so that they do not recognize an antigen which is present in the body and therefore only attack invading pathogens; however when this process is disrupted these B and T cells will recognize cells of the body and attack them as if they were a pathogen. These diseases can be focused on the attack of specific organs or the body as a whole leading to devastating and often lethal consequences.   Recent studies have implicated a small protein (SAP) which is encoded by the SH2D1A gene in the manifestation of autoimmune diseases such as Systematic Lupus Erythematosus, Rheumatoid Arthritus, and Myasthenia Gravis.  This intracellular protein contains a single SH2 domain which binds to a family of receptors (known as the SLAM receptors) and is  implicated in a number of immune system functions including the differentiation and production of T cell subsets.  This protein acts in two ways: 1. It has the capacity to bind and activate the protein Fyn which is critical for the signaling pathways involved in cell growth and differentiation  2. It prevents the binding of inhibitory proteins SHIP1 and SHP1 which act to impede cell growth and differentiation.  Therefore the presence of the SAP protein presents a two fold mechanism for cell growth and differentiation which helps explain why it is a key regulator of immunce cell functions.

A recent paper published in the November 1st addition of the Journal of Biochemistry examined the role of SAP in the regulation of the autoimmune disease Collagen-induced Arthritus (CIA).  This study induced murine CIA (similar to Rheumatoid Arthritis in humans) and altered the expression of SH2D1A in order to elucidate the role SAP plays in disease progression.  The authors of the paper found that when the SH2D1A gene was eliminated in the mice using a Cre-Lox system the mice did not develop CIA while the genetically normal mice did.  The implication of this initial test demonstrated that SAP must be playing  some kind of role in the progression of this autoimmune disease.  To further this investigation, researchers then used the same Cre-Lox system to eliminate the SH2D1A gene (and thus the formation of SAP) but utilized different promoter regions which were specific to B cell or T cells.  This meant that half of the mice had the gene deleted in their B cells only and the other half had the gene deleted in their T cells only.  The results of this demonstrated that when the gene was deleted from B cells there was no change in the disease course but when the gene was deleted in T cells the mice did not develop CIA.  So essentially SAP plays role in the development of T cells likely through its binding of SLAM receptors and concurrent phosphorylation and activation of the Fyn protein.  To test this idea, a final line of mice were induced with CIA but this time the mice expressed a different allele in which the SAP protein could bind to the SLAM receptors but not Fyn.  When the disease induction was given in a high dose the inability of SAP to bind and activate Fyn made no difference in the disease incidence and only a slight decrease in disease progression.  In contrast, when the disease was induced with a low dose of the antigen only half the mice developed CIA and the disease progression was even more reduced.  This would indicate that the binding of SAP to Fyn IS (in fact) necessary for the course of the disease.

The Road to Unconventional Immune System Memory

            

One of the coolest parts of the human immune system is its ability to remember previous exposure to viruses, bacteria, or other foreign invaders.  This is crucial in creating effective vaccines that prevent humans from contracting potentially fatal diseases.  If an invader is remembered, the immune system can launch a highly specific attack and prevent the person from ever getting sick.  However, this memory is not well understood by scientists.  As more and more studies are completed, new information about new subsets of cell types involved in or capable of memory is being released.  For example, you may know how long it takes to drive from Philadelphia to Denver, but what good is that if you don’t know what roads to take?  This same idea can be applied to the memory function of the immune system.  It’s great that scientists know that once a person is infected, certain cell types can remember the invader, but it’s difficult to promote a memory response if it’s unknown how the response even occurs.

            

General Memory B Cell Development

A recent paper published in The Journal of Immunology explores the road to a memory response.  The two big cell types involved in the pathway they explore are T and B cells.  The T cells involved help to activate B cells, which then produce antibodies.  These are small proteins that circulate through the body are responsible for “tagging” foreign bodies, or antigens, for destruction by other immune cells or neutralizing the effect of the foreign body.  Antibodies come in different structures with different functions, and can switch structures during the development and maturation of the B cell from a naïve cell to memory cell.  The two structures the researchers look at are IgM, which are usually produced by naïve cells that haven’t switched antibody type yet, and IgG, which are usually produced by B cells that have fully matured into memory B cells.  However, recent studies have shown that there are also memory IgM B cells, but their characteristics, purpose, and development are unclear.  Immune cells are often identified and characterized by the molecules expressed on their cell surface.  Called CD markers, or cluster of differentiation, they allow scientists to give a unique expression pattern to help identify and isolate new types of immune cells.  In the quest to understand the memory IgM B cells, one of the things the authors tried to undercover was a unique CD expression pattern on these cells.  They also looked at a mouse model of human ehrlichiosis, a bacterial infection from ticks, to explore the necessity of a T cell-B cell interaction for the activation of these IgM memory cells.  The also used this model to look at a secondary exposure to an antigen and determine the connection between these new memory cells and typical IgG memory 

A Novel Role for Controlling GI Tract Bacteria

The gastrointestinal (GI) tract is covered with harmless bacteria, bacteria which are somehow able to evade the immune system cells that heavily populate this area. These bacteria are commensal, meaning they that both the bacteria and the organism they reside in are able to benefit from their presence in the gut. It has previously been shown that children who have increased diversity of bacteria in their GI tract during infancy are less prone to developing allergies when they reach school age ¹. It is also known that these bacteria play an important role in helping with the digestion of food, providing vitamin K, helping protect the colon from the invasion of harmful bacteria, and helping to educate the immune system to differentiate between harmless and harmful bacteria². However, the mechanism employed by these bacteria that allows them to reside in the GI tract without being attacked by the hosts immune cells is not well understood.

One type of cell found in the immune system is the B cell, which secretes antibodies, or proteins that neutralize an infectious pathogen, stopping it from harming the host. After these cells encounter a pathogen, they mature into plasma cells and go through isotype switching, a process that allows the cells to change the type of antibody they secrete. Before this switch occurs, B cells secrete an antibody called IgG, but after the switch, they start creating an antibody that specifically targets the type of pathogen that they came in contact with. It is already known that plasma cells in the GI tract secrete the antibody IgA, but it is unknown what supports this class switching and its role in facilitating homeostatic balance between the bacteria in the gut and the host's immune system.

Jorg H. Fritz and associates found that nitric oxide (NO), which is produced by inducible nitric oxide synthase (iNOS) was necessary for the isotype switching of B-cells in the GI tract to IgA producing plasma cells. They had already found that mice who lack lymphotoxin, a chemical that activates the production of the iNOS, also lack IgA. So, they hypothesized that iNOS may cause the B-cell to isotype switch to IgA secreting plasma cells.

Bye-Bye B Cells, Hello MS Treatment

Multiple sclerosis is a chronic inflammatory disease that affects the brain and spinal cord, or central nervous system (CNS), leading to sensory and motor impairments. MS is more common in women than in men and is typically diagnosed between the ages of 20 and 40. Approximately 400,000 individuals in the United States currently have MS and more than 2.1 million people worldwide live with the disease. MS is diagnosed as one of two forms, either relapsing-remitting (RRMS) or primary progressive (PPMS). The vast majority of patients are initially diagnosed with RRMS, which is characterized by periods of exacerbation, or flare-ups, followed by periods of remission. Patients with PPMS do not experience remissive phases. Most of the medications approved for MS treatment are aimed toward ameliorating the relapsing-remitting disease course. Currently, MS is commonly treated with an interferon beta (IFN beta) drug, which reduces disease activity, in combination with other medications that target the various symptoms experienced by patients (2).

The clinical presentation of MS varies from person to person; however, pathologically, the disease results from an autoimmune attack on myelin sheath (a protective covering around nerve fibers). Immune cells (lymphocytes) become self-reactive against certain proteins that make up myelin and subsequently destroy it. This process is called demyelination. When the myelin sheath is damaged, signaling between nerve cells becomes slowed or prevented altogether. As a result, simple tasks like walking become quite difficult, and patients may experience vision impairments, episodes of numbness and tingling, loss of balance and coordination, as well as other symptoms. Unfortunately, the mechanism through which an individual develops MS is not entirely understood, and therefore, the repertoire of treatment targets is limited. In order to gain a better understanding of the cause and progression of MS, researchers use various animal models of the disease. The most commonly used MS model is experimental autoimmune encephalomyelitis (EAE), which can be induced in a variety of animal species including certain rodents and non-human primates. In the upcoming November issue of the Journal of Neuropathology and Experimental Neurology, a study by Kap and colleagues investigates whether or not B cell depletion (an experimental treatment for MS) is a valid therapeutic target (1). The authors employed an EAE study in the common marmoset (monkey species). Marmosets were first utilized to examine the clinical and pathological features of MS in 1996, and have been found to exhibit a disease course more closely related to human MS than that observed in rodent models. The marmoset EAE model demonstrates widespread demyelination in both white matter and grey matter of the CNS, strongly resembling the conditions of MS in humans. Furthermore, marmosets have similar immune and nervous system genes to humans, establishing another advantage of using this model (3).

A New Take on the Importance of Memory

When you hear the word memory your initial thought may be to think of your brain.  However, the memory of cells plays an integral role in other systems of our bodies as well. Memory is crucial to the immune system’s ability to efficiently fight off infections.  Our bodies are miraculously able to generate antibodies against viruses while maintaining anti-viral antibody secreting cells to protect us from future attack by the same virus. While antibodies we make span a month, they retain the means of reproducing them for a lifetime (3).

In 1796, Edward Jenner’s noted that dairymaids and farmers lacked the smallpox that was disfiguring and killing whole villages. Cowpox during this time suffered from a similar disorder, cowpox, in which cattle experienced similar but less severe symptoms than humans (3). He exposed an 8-year-old boy first with fluid from an infected cow then two months later he inoculated the boy with smallpox. Sure enough, the boy’s immune system was able to remember how to fight the infection (3). This experiment, although clearly unethical, proved to be the first successful vaccination that would lead to the development of future vaccinations for a plethora of viruses. Jenner paved the way for future scientists to build off his idea of weakening pathogens in the laboratory to inoculate patients with in order to protect them from future exposure to that pathogen.  Today scientists continue to build off of this demonstration with the intent to better understand the cellular and molecular mechanisms governing this profound observation and experiment. 

Naturally killing rheumatoid arthritis

To get this semester's blogging off and running (no one wants to be the first to post on an empty blog!), here is my take on a new PNAS paper from the Cantor lab:

            Rheumatoid arthritis (RA) is an autoimmune inflammatory disease that affects around 1.3 million people in the United States. Found more commonly in women than men, this disease causes pain and swelling in the joints, and can lead to cartilage and bone loss, and joint deformity. RA is commonly treated with methotrexate, in combination with other drugs, but treatments can be expensive, with lifetime direct costs of up to $180,000 per patient (in 2010 dollars). These treatments can also have adverse side effects. The prevalence of RA in the U.S. is increasing as the population ages, suggesting a need for continued research into the causes of, and potential new therapeutics for, RA.

            At its core, RA is a disease of multiple immune cell types. One component is B cells, which produce antibodies that recognize “self” proteins found in connective tissue. A second component is “helper” T cells (also termed CD4 T cells), which help B cells produce antibody, and which contribute to an inflammatory state in the joints. A study published this week in the Proceedings of the National Academy of Sciences by Leavenworth and colleagues further refines the contribution of different CD4 T cell subsets in RA, and defines a new role for yet a third cell type, natural killer (NK) cells, in suppressing the development of RA. To do this, the authors used an experimental mouse model of RA, induced by injection of type II collagen, a prominent component of connective tissue, under the skin. This model (collagen-induced arthritis; CIA) causes many of the same symptoms as human RA, and has been used to test a number of new treatments for RA (1).