Autoimmune Disease

Autoimmune Disease

Write a short note on autoimmune disease.
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.

Normally, the immune system of the body is able to distinguish self from non-self antigens by the following mechanisms:

• Clonal elimination: According to this theory during embryonic development, T cells maturing in the thymus acquire the ability to distinguish self from non-self. These T cells are then eliminated by apoptosis for the tolerant individual.
• Concept of clonal energy: According to this mechanism, T lymphocytes that have acquired the ability to distinguish self from non-self are not eliminated but instead become non-responsive and inactive.
• Suppressor T cells: According to this mechanism, the tolerance is achieved by a population of specific suppressor T cells which do not allow the antigen-responsive cells to proliferate and differentiate.

Autoimmune disease list

Autoimmune disease Pathogenesis

• Immunological factors: Failure of immunological mechanisms of tolerance initiates autoimmunity. These mechanisms are as follows:
  • Polyclonal activation of B cells: B cells may be directly activated by stimuli such as infection with microorganisms and their products leading to bypassing of T cell tolerance.
  • Generation of self-reacting B cell clones may also lead to bypassing of T cell tolerance.
  • Decreased T suppressor and increased T helper cell activity. Loss of T suppressor cells and an increase in T helper cell activities may lead to high levels of auto-antibody production by B cells contributing to autoimmunity.
  • Fluctuation of immunological network control may cause failure of mechanisms of immune tolerance.
  • Sequestered antigen released from tissues: ‘Selfantigen’ which is completely sequestered may act as ‘foreign-antigen’ if introduced into the circulation later.
• Genetic factors: There is evidence in support of genetic factors in the pathogenesis of autoimmunity as under:
  • There is increased expression of Class II HLA antigens on tissues involved in autoimmunity
  • There is an increased familial incidence of some autoimmune disorders.
• Microbial factors: Infection with microorganisms, particularly viruses (For Example. EBV infection), and less often bacteria (For Example. streptococci, Klebsiella) and M mycoplasma have been implicated in the pathogenesis of autoimmune diseases.

Autoimmune disease causes

Types of Autoimmune Diseases

Depending upon the type of autoantibody formation, autoimmune diseases are broadly classified into two groups:

• Organ-specific diseases: In these, the autoantibodies formed react specifically against an organ or target tissue component and cause its chronic inflammatory destruction. The tissues affected are endocrine glands, alimentary tract, blood cells, and various other tissues and organizers:
• Non­organ specific diseases: These are diseases in which a number of autoantibodies are formed which react with antigens in many tissues and thus cause systemic lesions. Examples of this group are various systemic collagen diseases.