Autoimmunity
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| Autoimmunity Classification and external resources | |
| ICD-9 | 279.4 |
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| OMIM | 109100 |
| DiseasesDB | 28805 |
| MeSH | D001327 |
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Phone:617-525-6884
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Overview
Autoimmunity is the failure of an organism to recognize its own constituent parts (down to the sub-molecular levels) as self, which results in an immune response against its own cells and tissues. Any disease that results from such an aberrant immune response is termed an autoimmune disease. Prominent examples include Coeliac disease, diabetes mellitus type 1 (IDDM), systemic lupus erythematosus (SLE), Sjögren's syndrome, multiple sclerosis (MS), Hashimoto's thyroiditis, Graves' disease, idiopathic thrombocytopenic purpura, and rheumatoid arthritis (RA). See List of autoimmune diseases.
The misconception that an individual's immune system is totally incapable of recognising self antigens is not new. Paul Ehrlich, at the beginning of the twentieth century, proposed the concept of horror autotoxicus, wherein a 'normal' body does not mount an immune response against its own tissues. Thus, any autoimmune response was perceived to be abnormal and postulated to be connected with human disease. Now, it is accepted that autoimmune responses are vital to the development and functioning of vertebrate immune systems, and central to the development of immunological tolerance to self-antigens. The latter concept has been termed natural autoimmunity. Autoimmunity should not be confused with alloimmunity.
Low-level autoimmunity
While a high level of autoimmunity is unhealthy, a low level of autoimmunity may actually be beneficial. First, low-level autoimmunity might aid in the recognition of neoplastic cells by CD8+ T cells, and thus reduce the incidence of cancer.
Second, autoimmunity is likely to have a role in allowing a rapid immune response in the early stages of an infection when the availability of foreign antigens limits the response (i.e., when there are few pathogens present). In their study, Stefanova et al. (2002) injected an anti-MHC Class II antibody into mice expressing a single type of MHC Class II molecule (H-2b) to temporarily prevent CD4+ T cell-MHC interaction. Naive CD4+ T cells (those that have not encountered any antigens before) recovered from these mice 36 hours post-anti-MHC administration showed decreased responsiveness to the antigen pigeon cytochrome C peptide, as determined by Zap-70 phosphorylation, proliferation, and Interleukin-2 production. Thus Stefanova et al. (2002) demonstrated that self-MHC recognition (which, if too strong may contribute to autoimmune disease) maintains the responsiveness of CD4+ T cells when foreign antigens are absent.[1] This idea of autoimmunity is conceptually similar to play-fighting. The play-fighting of young cubs (TCR and self-MHC) may result in a few scratches or scars (low-level-autoimmunity), but is beneficial in the long-term as it primes the young cub for proper fights in the future.
Immunological tolerance
Pioneering work by Noel Rose and Witebsky in New York, and Roitt and Doniach at University College London provided clear evidence that autoimmune diseases are a result of loss of tolerance. An essential prerequisite for the pathogenesis of autoimmune diseases is indeed the breakage of immunological tolerance, which is the ability of an individual to differentiate 'self' from 'non-self'. This breakage leads to the immune system's mounting an effective and specific immune response against self determinants. The exact genesis of immunological tolerance is still elusive, but several theories have been proposed since the mid-twentieth century to explain its origin.
Three hypotheses have gained widespread attention among immunologists:
- Clonal Deletion theory, proposed by Burnet, according to which self-reactive lymphoid cells are destroyed during the development of the immune system in an individual. For their work Frank M. Burnet and Peter B. Medawar were awarded the 1960 Nobel Prize in Physiology or Medicine "for discovery of acquired immunological tolerance".
- Clonal Anergy theory, proposed by Nossal, in which self-reactive T- or B-cells become inactivated in the normal individual and cannot amplify the immune response.[1]
- Idiotype Network theory, proposed by Jerne, wherein a network of antibodies capable of neutralizing self-reactive antibodies exists naturally within the body.[1]
In addition, two other theories are under intense investigation:
- The so-called "Clonal Ignorance" theory, according to which host immune responses are directed to ignore self-antigens[1]
- The "Suppressor population" or "Regulatory T cell" theories, wherein regulatory T-lymphocytes (commonly CD4+FoxP3+ cells, among others) function to prevent, downregulate, or limit autoaggressive immune responses.
Tolerance can also be differentiated into 'Central' and 'Peripheral' tolerance, on whether or not the above-stated checking mechanisms operate in the central lymphoid organs (Thymus and Bone Marrow) or the peripheral lymphoid organs (lymph node, spleen, etc., where self-reactive B-cells may be destroyed). It must be emphasised that these theories are not mutually exclusive, and evidence has been mounting suggesting that all of these mechanisms may actively contribute to vertebrate immunological tolerance.
Genetic Factors
Certain individuals are genetically susceptible to developing autoimmune diseases. This susceptibility is associated with multiple genes plus other risk factors. Genetically-predisposed individuals do not always develop autoimmune diseases.
Three main sets of genes are suspected in many autoimmune diseases. These genes are related to:
The first two, which are involved in the recognition of antigens, are inherently variable and susceptible to recombination. These variations enable the immune system to respond to a very wide variety of invaders, but may also give create lymphocytes, which are capable of self-reactivity.
Scientists such as H. McDevitt, G. Nepom, J. Bell and J. Todd have also provided strong evidence to suggest that certain MHC class II allotypes are strongly correlated with specific autoimmune diseases:
- HLA DR2 is strongly positively correlated with Systemic Lupus Erythematosus and multiple sclerosis, and negatively correlated with DM Type 1.
- HLA DR3 is correlated strongly with Sjögren's syndrome, myasthenia gravis, SLE, and DM Type 1.
- HLA DR4 is correlated with the genesis of rheumatoid arthritis, Type 1 diabetes mellitus, and pemphigus vulgaris.
Fewer correlations exist with MHC class I molecules. The most notable and consistent is the association between HLA B27 and ankylosing spondylitis. Correlations may exist between polymorphisms within class II MHC promoters and autoimmune disease.
The contributions of genes outside the MHC complex remain the subject of research, in animal models of disease (Linda Wicker's extensive genetic studies of diabetes in the NOD mouse), and in patients (Brian Kotzin's linkage analysis of susceptibility to SLE).
Sex
Sex also seems to have a major role in the development of autoimmunity; most of the known autoimmune diseases tend to show a female preponderance, the most important exceptions being ankylosing spondylitis, which has a male preponderance, and Crohn's disease, which has a roughly equal prevalence in males and females. The reasons for this are unclear. Apart from inherent genetic susceptibility, several animal models suggest a role for sex steroids.
It has also been suggested that the slight exchange of cells between mothers and their children during pregnancy may induce autoimmunity.[1] This would tip the gender balance in the direction of the female.
Another theory suggests the female high tendency to get autoimmunity is due to an imbalanced X chromosome inactivation.[1]
Environmental Factors
An interesting inverse relationship exists between infectious diseases and autoimmune diseases. In areas where multiple infectious diseases are endemic, autoimmune diseases are quite rarely seen. The reverse, to some extent, seems to hold true. The hygiene hypothesis attributes these correlations to the immune manipulating strategies of pathogens. Whilst such an observation has been variously termed as spurious and ineffective, according to some studies, parasite infection is associated with reduced activity of autoimmune disease.[1][1][1]
The putative mechanism is that the parasite attenuates the host immune response in order to protect itself. This may provide a serendipitous benefit to a host that also suffers from autoimmune disease. The details of parasite immune modulation are not yet known, but may include secretion of anti-inflammatory agents or interference with the host immune signaling.
A paradoxical observation has been the strong association of certain microbial organisms with autoimmune diseases. For example, Klebsiella pneumoniae and coxsackievirus B have been strongly correlated with ankylosing spondylitis and DM Type 1, respectively. This has been explained by the tendency of the infecting organism to produce super-antigens that are capable of polyclonal activation of B-lymphocytes, and production of large amounts of antibodies of varying specificities, some of which may be self-reactive (see below).
Certain chemical agents and drugs can also be associated with the genesis of autoimmune conditions, or conditions that simulate autoimmune diseases. The most striking of these is the drug-induced lupus erythematosus. Usually, withdrawal of the offending drug cures the symptoms in a patient.
Overexposure to pesticides and toxins may also induce autoimmunity.
Pathogenesis of autoimmunity
Several mechanisms are thought to be operative in the pathogenesis of autoimmune diseases, against a backdrop of genetic predisposition and environmental modulation. It is beyond the scope of this article to discuss each of these mechanisms exhaustively, but a summary of some of the important mechanisms have been described:
- T-Cell Bypass - A normal immune system requires the activation of B-cells by T-cells before the former can produce antibodies in large quantities. This requirement of a T-cell can be bypassed in rare instances, such as infection by organisms producing super-antigens, which are capable of initiating polyclonal activation of B-cells, or even of T-cells, by directly binding to the β-subunit of T-cell receptors in a non-specific fashion.
- Molecular Mimicry - An exogenous antigen may share structural similarities with certain host antigens; thus, any antibody produced against this antigen (which mimics the self-antigens) can also, in theory, bind to the host antigens, and amplify the immune response. The most striking form of molecular mimicry is observed in Group A beta-haemolytic streptococci, which shares antigens with human myocardium, and is responsible for the cardiac manifestations of Rheumatic Fever.
- Idiotype Cross-Reaction - Idiotypes are antigenic epitopes found in the antigen-binding portion (Fab) of the immunoglobulin molecule. Plotz and Oldstone presented evidence that autoimmunity can arise as a result of a cross-reaction between the idiotype on an antiviral antibody and a host cell receptor for the virus in question. In this case, the host-cell receptor is envisioned as an internal image of the virus, and the anti-idiotype antibodies can react with the host cells.
- Cytokine Dysregulation - Cytokines have been recently divided into two groups according to the population of cells whose functions they promote: Helper T-cells type 1 or type 2. The second category of cytokines, which include IL-4, IL-10 and TGF-β(to name a few), seem to have a role in prevention of exaggeration of pro-inflammatory immune responses.
- Dendritic cell apoptosis - immune system cells called dendritic cells present antigens to active lymphocytes. Dendritic cells that are defective in apoptosis can lead to inappropriate systemic lymphocyte activation and consequent decline in self-tolerance.[1]
The roles of specialized immunoregulatory cell types, such as regulatory T cells, NKT cells, γδ T-cells in the pathogenesis of autoimmune disease are under investigation.
Classification
Autoimmune diseases can be broadly divided into systemic and organ-specific or localised autoimmune disorders, depending on the principal clinico-pathologic features of each disease.
- Systemic syndromes include SLE, Sjögren's syndrome, Scleroderma, Rheumatoid Arthritis and polymyositis.
- Local syndromes may be endocrinologic (Diabetes Mellitus Type 1, Hashimoto's thyroiditis, Addison's disease etc.), dermatologic (pemphigus vulgaris), haematologic (autoimmune haemolytic anaemia), neural (multiple sclerosis) or can involve virtually any circumscribed mass of body tissue.
Diagnosis
Diagnosis of autoimmune disorders largely rests on accurate history and physical examination of the patient, and high index of suspicion against a backdrop of certain abnormalities in routine laboratory tests (example, elevated C-reactive protein). In several systemic disorders, serological assays which can detect specific autoantibodies can be employed. Localised disorders are best diagnosed by immunofluorescence of biopsy specimens.
Treatments
Current treatments for autoimmune disease are usually immunosuppressive, anti-inflammatory, or palliative.[1] Non-immune therapies, such as hormone replacement in Hashimoto's thyroiditis or DM Type 1 treat outcomes of the autoaggressive response. Dietary manipulation limits the severity of celiac disease. Steroidal or NSAID treatment limits inflammatory symptoms of many diseases. IVIG is used for CIDP and GBS. More specific immunomodulatory therapies, such as the TNFα antagonists etanercept, have been shown to be useful in treating RA. These immunotherapies may be associated with increased risk of adverse effects, such as susceptibility to infection.
Autoantibodies are used to diagnose many autoimmune diseases. The levels of autoantibodies are measured to determine the progress of the disease.
Helminthic therapy has developed based on these observations and involves inoculation of the patient with specific parasitic intestinal nematodes (helminths). There are currently two closely-related treatments available, inoculation with either Necator americanus, commonly known as hookworms, or Trichuris Suis Ova, commonly known as Pig Whipworm Eggs. Research is available that demonstrates this approach is highly effective in treating a variety of autoimmune disorders, including Crohn's, Ulcerative Colitis, Asthma, allergies, Multiple Sclerosis, and chronic inflammatory disorders..[1] [1][1][1][1] [1]
See also
References
External links
- American Autoimmune Related Diseases Association: a nonprofit advocacy
- Immune Tolerance Network: a research-oriented resource
- Nobel Prize: The 1960 Nobel Prize in Physiology or Medicine was awarded to Frank M. Burnet and Peter B Medawar
Immune system / Immunology | |
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| Systems | Adaptive immune system vs. Innate immune system • Humoral immune system vs. Cellular immune system • Complement system (Anaphylatoxins) • Intrinsic immune system |
| Antibodies and antigens | Antibody (Monoclonal antibodies, Polyclonal antibodies, Autoantibody) • Allotype • Isotype • Idiotype • Antigen (Superantigen) |
| Immune cells | White blood cells (T cell, B cell, NK cell, Mast cell, Basophil, Eosinophil) • Phagocyte (Neutrophil, Macrophage, Dendritic cell) • Antigen-presenting cell • Reticuloendothelial system |
| Immunity vs. tolerance | Immunity • Autoimmunity • Allergy • Tolerance (Central) • Immunodeficiency |
| Immunogenetics | Somatic hypermutation • V(D)J recombination • Immunoglobulin class switching • MHC / HLA |
| Substances | Cytokines • Opsonin • Cytolysin |
| Other | Inflammation • Epitope (Hapten) • Cross-reactivity |
WikiDoc Research Resources for Autoimmunity (Click show to right to view) | |
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| Articles on Autoimmunity | Most recent articles on Autoimmunity • Most cited articles on Autoimmunity • Review articles on Autoimmunity • Articles on Autoimmunity in N Eng J Med, Lancet, BMJ |
| Media (Slides, Video, Images, MP3) on Autoimmunity | Powerpoint slides on Autoimmunity • Images of Autoimmunity • Photos of Autoimmunity • Podcasts & MP3s on Autoimmunity • Videos on Autoimmunity |
| Evidence Based Medicine Regarding Autoimmunity | Cochrane Collaboration on Autoimmunity • Bandolier on Autoimmunity • TRIP on Autoimmunity |
| Cost Effectiveness of Autoimmunity | Cost Effectiveness of Autoimmunity |
| Clinical Trials Involving Autoimmunity | Ongoing Trials on Autoimmunity at Clinical Trials.gov • Trial results on Autoimmunity • Clinical Trials on Autoimmunity at Google |
| Guidelines / Policies / Government Resources (FDA/CDC) Regarding Autoimmunity | US National Guidelines Clearinghouse on Autoimmunity • NICE Guidance on Autoimmunity • NHS PRODIGY Guidance • FDA on Autoimmunity • CDC on Autoimmunity |
| Textbook Information on Autoimmunity | Books and Textbook Information on Autoimmunity |
| Pharmacology Resources on Autoimmunity | Dosing of Autoimmunity • Drug interactions with Autoimmunity • Side effects of Autoimmunity • Allergic reactions to Autoimmunity • Overdose information on Autoimmunity • Carcinogenicity information on Autoimmunity • Autoimmunity in pregnancy • Pharmacokinetics of Autoimmunity • |
| Genetics, Pharmacogenomics, and Proteinomics of Autoimmunity | Genetics of Autoimmunity • Pharmacogenomics of Autoimmunity • Proteomics of Autoimmunity |
| Newstories on Autoimmunity | Autoimmunity in the news • Be alerted to news on Autoimmunity • News trends on Autoimmunity |
| Commentary on Autoimmunity | Blogs on Autoimmunity |
| Patient Resources on Autoimmunity | Patient resources on Autoimmunity • Discussion groups on Autoimmunity • Patient Handouts on Autoimmunity • Directions to Hospitals Treating Autoimmunity • Risk calculators and risk factors for Autoimmunity |
| Healthcare Provider Resources on Autoimmunity | Symptoms of Autoimmunity • Causes & Risk Factors for Autoimmunity • Diagnostic studies for Autoimmunity • Treatment of Autoimmunity |
| Continuing Medical Education (CME) Programs on Autoimmunity | CME Programs on Autoimmunity |
| International Resources on Autoimmunity | Autoimmunity en Espanol • Autoimmunity en Francais |
| Business Resources on Autoimmunity | Autoimmunity in the Marketplace • Patents on Autoimmunity |
| Informatics Resources on Autoimmunity | List of terms related to Autoimmunity |
bg:Автоимунитет ca:Malaltia autoimmunitària cs:Autoimunita da:Autoimmun de:Autoimmunerkrankungfr:Maladie auto-immune hr:Autoimune bolesti it:Malattia autoimmunitaria he:מחלת חיסון עצמי hu:Autoimmun betegség nl:Auto-immuunziekte ja:自己免疫疾患 no:Autoimmun sykdomsk:Autoimunitná choroba sr:Аутоимуни поремећај fi:Autoimmuunisairaus sv:Autoimmunitetuk:Автоімунна патологія
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Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
