Dr. McGargill earned her PhD at the University of Minnesota in Dr. Kristin Hogquist’s lab. There she studied T cell development, focusing on how autoreactive T cells are deleted during development. As a postdoc at the University of California, San Diego, she worked with Dr. Stephen Hedrick to examine how mature T cells are regulated molecularly so that they don’t react to normal, healthy tissue. Now at St. Jude Children’s Research Hospital, she continues to study immune system regulation and the fine line between positive response to infections and negative autoimmune reactions. The lab studies multiple sclerosis, type 1 diabetes, and is studying the immune response to the conserved epitopes of influenza viruses to aid in the design of a universal influenza vaccine.
NS: What led you to apply to the NanoString® Autoimmunity Grant program?
MM: I received an email from a colleague describing the technology and the grant opportunity. We have a project where we know autoimmunity is involved but we do not how it is occurring. This technology gives us the opportunity to look at multiple factors at once.
NS: What are the goals of this project specific to the grant, and what do you hope to learn?
MM: We study the immune response to conserved epitopes of influenza viruses. Understanding how we make a strong response to the conserved portions is important in designing universal influenza vaccines. We use a mouse model in which we can increase the amounts of antibodies that are specific to more than one subtype of influenza, often referred to as influenza cross-reactive antibodies. We treat mice with a low dose of rapamycin when we give them the influenza vaccine. We previously showed that this technique protects mice against subsequent infection with multiple different subtypes of influenza. Control mice given that same vaccine are only protected against the specific strain of influenza used in the vaccine. We know, therefore, that rapamycin is altering the immune response, but we don’t know how. And while these mice display a positive protection by generating a broader spectrum of anti-influenza antibodies, they unfortunately also have more autoreactive antibodies. This suggests that one reason that the antibodies to the conserved portions of influenza are so rare is that these epitopes may have a greater potential to induce antibodies against self-proteins. We want to understand the mechanisms by which these anti-self-antibodies are both generated and deleted. In developing a universal influenza vaccine, we do not want to generate antibodies that would be cross-reactive and induce autoimmune disease. Moreover, understanding how ‘anti-self’ antibodies are generated in the course of pathogenic infection applies broadly to many different autoimmune diseases. With this project in particular, we hope to learn which subsets of B cells are contributing to the autoimmunity and which of the pathways impacted by the rapamycin also contribute to autoimmunity.
NS: Why does treating mice with rapamycin result in production of antibodies that more broadly target flu viruses?
MM: We know that rapamycin decreases germinal center formations. Our initial thinking was that this reduction resulted in a lower number of high affinity IgG antibodies specific to the influenza variable regions. We thought the lack of competition allowed antibodies to the conserved regions to flourish. What we have seen, however, is that eliminating the high affinity, variable-specific antibodies by treatments other than rapamycin is not sufficient to allow the cross-reactive antibodies to be more prevalent. Our current thinking is that under normal conditions, the B cells creating cross-reactive antibodies are deleted out and that rapamycin is interfering with and preventing that deletion, giving rise to a broader repertoire of B cells.
MM: We need to understand how B cells are typically deleted in a healthy individual in order to understand how we can intervene when the system goes wrong. With regards to universal influenza vaccine development, if we can identify the pathways that are different then we can ensure that our universal vaccine candidates are not triggering an autoreactive pathway.
NS: What do you think the role of gene expression profiling is in subtyping various autoimmune diseases?
MM: I don’t think there will be a case where just one gene is responsible for an autoimmune disease. More likely, there will be a number of factors that determine whether there is autoimmunity or not. When you can look at a whole panel of different gene expression levels it’s possible to identify patterns or pathways that result in or contribute to autoimmune disease.
NS: What parts of the immune system are at play during a vaccine response that are also implicated in autoimmune disease?
MM: Any exposure, be it infection or vaccination, can increase the risk of autoimmune disease to some extent. We have focused on the antibody part, starting with the B cells. The biggest risk factor across the board is the human leukocyte antigen type. We all have autoantibodies and autoreactive B cells, but most people don’t have autoimmune disease. If the immune system’s fail-safe mechanisms break and someone develops an autoimmune disease, that disease will likely have been shaped by their history of infection and pathogen exposure.
NS: How does this process get hijacked into the development of autoimmune disorders?
MM: While the B cells are fine-tuning their repertoire and rearranging their receptors, they could generate an autoreactive response simply by random chance. If the resulting self-directed antibody is close enough to the pathogenic epitope, then it can increase the amplification of self-reactive B cells along with the infection. There are also cases of epitope mimicry, where the pathogenic antigen closely mirrors a host protein as a way to evade immune responses. When this is successful it can also lead to autoimmune disease.
NS: What signals the immune system that an infection is winding down so that the immune system can return to its surveillance state? What remains unknown about this process?
MM: There are many mechanisms in place to shut down the immune response. In an acute infection, once the innate immune response has subsided, the T and B cells will stop expanding. This can be signaled by the upregulation of negative regulatory molecules; it can also be a result of the absence of the antigen that initiated the expansion. Regulatory T cells play a role in shutting down the response, as well. There’s a lot we still don’t understand, including the role of different environmental factors, the patient’s age at the time of the infection, and the contribution of concurrent infections (to name a few).
NS: How do rates of autoimmune disease vary across different countries? Is there a noticeable difference between developed and developing nations?
MM: Developing nations tend to show a lower incidence of autoimmune disease. This can be due to genetic variation among populations, the environmental factors of a given region, and the hygiene hypothesis. This hypothesis suggests that when the immune system is fighting enough foreign pathogens it doesn’t target self-proteins enough to generate an autoimmune response.
NS: Why do certain autoimmune diseases such as multiple sclerosis (MS) tend to affect women more than men?
MM: As always, there are multiple factors that contribute to autoimmune disease. In MS, the evidence suggests that the fluctuation of hormone levels in women can impact autoimmunity. For example, there are high rates of remission in female MS patients during pregnancy. Immediately following delivery, there’s a higher rate of relapse, suggesting that the change in hormones during pregnancy can impact the disease. There’s also research that suggests that having two copies of the X chromosome can lead to the overexpression of genes that may contribute to a hyperactive immune system as compared to having only one X chromosome in males.
NS: How does the immune response involved in the MS pathway differ from the immune responses seen in other chronic inflammation disorders?
MM: The main difference is that the movement of the immune system cells into the central nervous system is physically restricted; a classic example of this is the blood-brain barrier. This barrier is not as tight as once thought to be so cells can still pass into these restricted areas, especially when inflammation is present. This will impact what cells can migrate across the barrier and how tolerance is induced.
NS: What immune cells are most critical to the development of MS?
MM: Most of what we know comes from mouse models. The autoreactive CD4 cells are the biggest contributor because they cause tissue inflammation and destruction. In addition, they help autoreactive B cells to generate autoantibodies. CD8 T cells are also autoreactive, contributing to the disease progression.
NS: What are the similarities in the immune mechanisms between MS and type 1 diabetes?
MM: There are a number of similarities, particularly with autoreactive T cells. Some of the same mechanisms that induce tolerance in T cells in type 1 diabetes are similar in MS. For example, Drak2 is a serine, threonine kinase expressed in T and B cells. When this gene is knocked out in mice it prevents the development of both MS and type 1 diabetes. The autoreactive T cells do not accumulate and attack the central nervous system or the pancreas (respectively) without Drak2.
NS: What are the most pressing challenges facing researchers studying autoimmune diseases?
MM: One of the biggest things is that even well-characterized diseases, such as lupus, consist of many diverse subtypes. Narrowing down the different subtypes of diseases will help us better understand their etiology and causes of the subtypes. Generally speaking, autoimmunity creates such a diverse panel of symptoms in individuals and it’s shaped by their environment. As we begin to understand these subtypes better then we can understand how these autoimmune diseases develop.
FOR RESEARCH USE ONLY. Not for use in diagnostic procedures.
For more information about the nCounter Autoimmune Profiling Panel, visit our website.