Autoimmunity
Question 1. Write a short note on autoimmunity.
Answer:
Autoimmunity is a state in which the body’s immune system fails to distinguish between “self” and “non-self” and reacts by the formation of autoantibodies against one’s own tissue antigens.
- There is a loss of tolerance to one’s own tissues.
- Autoimmunity is the opposite of immune tolerance.
Mechanism for the Development of Autoimmune Diseases Various theories are proposed to explain how normal controlling mechanism fails to maintain self-recognition.
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The following are the theories:
1. Hidden or sequestered antigen theory: In this theory, tissue antigens that are exposed to lymphoreticular development at the time of embryonic development are recognized as self-antigens and are unable to induce the immune response. Many of the autoantigens are not accessible to cells of the immune system as they are hidden inside a cell or tissue.
Such antigens are called sequestered antigens and though they are self-antigens but are treated as non-self-antigens. These antigens when come in contact with immunocompetent cells, they lead to an immune response and at the same time allow stimulated lymphocytes as well as antibodies to produce trauma or injury by reacting with them.
2. Neo antigens: In some circumstances, a native tissue antigen may be altered in some way by physical, chemical, or biological means and assume a new antigenic specificity. Altered antigen stimulates the immune reaction which damages native tissue antigens producing tissue injury.
3. Cross-reacting agents: Various microorganisms carry antigenic determinants that resemble the host cell component. These are cross-reacting agents. Infection by such microorganisms initiates an immune response that damages particular organs or tissue in the host.
4. Loss of immunoregulation: Loss of normal tolerance control due to loss of immunoregulation causes autoimmune disease. Defects or lack of efficiency in the lymphoid cell population can cause a loss of normal tolerance control.
5. Autoimmunity Genetic abnormalities: Various genetic abnormalities, i.e. mutation in an immunocompetent cell, or defect in the immunoglobulin gene can cause antigenic responsiveness to self-antigens leading to autoimmune diseases.
Pathogenesis of Autoimmunity The mechanism by which the immune tolerance of the body is broken causes autoimmunity.
- Autoimmunity Immunological factors:
- Failure of the immunological mechanism of tolerance initiates autoimmunity.
- Polyclonal activation of B cells: Production of self-reacting B cell clones because of certain stimuli, i.e. chemicals, bacterial products, enzymes, antibiotics, infection with some bacteria, viruses, and parasites.
- Generation of self-reacting B cell clone.
- Decreased T suppressor and increased T helper cell activity.
- Defects in isotype: Anti-idiotype network.
- Defects in thymus, in stem cell development and macrophage function.
- Sequestered antigen released from tissues.
- Autoimmunity Genetic factors:
- There is increased expression of class II HLA antigens on tissues involved in autoimmunity.
- There is an increased familial incidence of some autoimmune disorders.
- Autoimmunity Microbial factors: Infections with microorganisms particularly viruses, for example, EBV infection, less commonly by bacteria and mycoplasm.
Types of Autoimmune Diseases Depending upon the type of antibody formation:
- Organ-specific diseases: In these the autoantibodies formed react especially against an organ or target tissue component, for example, Hashimoto thyroiditis.
- Graves’ disease
- Myasthenia Graves.
- Insulin-dependent diabetes mellitus
- Idiopathic Addiction disease, etc.
- Non-organ-specific (systemic) or Diseases-causes systemic
- Lesions, for example, Systemic lupus erythematosus.
- Rheumatoid arthritis
- Scleroderma
- Polyartheritis nodosa
- Sjogren syndrome
- Reiter’s syndrome.
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