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Immune.pptx
1. Autoimmune diseases – General
features, enumerate systemic and organ
specific autoimmune diseases
2. Autoimmunity & Immune tolerance
• Autoimmunity is a state in which the body’s immune system fails to
distinguish between ‘self’ and ‘non-self’ and reacts by formation of
autoantibodies against one’s own tissue antigens.
• In other words, there is loss of tolerance to one’s own tissues;
autoimmunity is the opposite of immune tolerance.
• Immune tolerance is a normal phenomenon present since foetal life
and is defined as the ability of an individual to recognise self tissue
and antigens
4. Pathogenesis (Theories) Of Autoimmunity
• The mechanisms by which immune tolerance of the body is broken causes
autoimmunity.
• These mechanisms or theories of autoimmunity may be immunological, genetic,
and microbial, all of which may be interacting.
• 1. Immunological factors. Failure of immunological mechanisms of tolerance
initiates autoimmunity. These mechanisms are as follows:
• i) 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.
• ii) Generation of self-reacting B cell clones may also lead to bypassing of T cell
tolerance.
• iii) Decreased T suppressor and increased T helper cell activity.
5. • iv) Fluctuation of anti-idiotype network control may cause failure of
mechanisms of immune tolerance.
• v) Sequestered antigen released from tissues. ‘
• Self-antigen’ which is completely sequestered may act as ‘foreign-
antigen’ if introduced into the circulation later.
• For example, in trauma to the testis, there is formation of anti-sperm
antibodies against spermatozoa; similar is the formation of
autoantibodies against lens crystallin.
6. 2. Genetic factors. There is evidence in support of genetic factors in the
pathogenesis of autoimmunity as under:
i) There is increased expression of Class II HLA antigens on tissues involved in
autoimmunity.
ii) There is increased familial incidence of some of the autoimmune
disorders.
3. Microbial factors. Infection with microorganisms, particularly viruses (e.g.
EBV infection), and less often bacteria (e.g. streptococci, Klebsiella) and
mycoplasma, has been implicated in the pathogenesis of autoimmune
diseases.
However, a definite evidence in support is lacking.
7. Types & Examples Of Autoimmune Diseases
Depending upon the type of autoantibody formation, autoimmune
diseases are broadly classified into 2 groups:
• 1. Organ specific diseases: Autoantibodies formed react specifically
against an organ or target tissue component and cause its chronic
inflammatory destruction.
• The tissues affected are endocrine glands (e.g. thyroid, pancreatic
islets of Langerhans, adrenal cortex), alimentary tract, blood cells and
various other tissues and organs.
8. • 2. Organ non-specific (Systemic) diseases. These are diseases in
which a number of autoantibodies are formed which react with
antigens in many tissues and thus cause systemic lesions.
• The examples of this group are various systemic collagen diseases.
Autoimmunity results from multiple factors, including susceptibility genes that may interfere with self-tolerance and environmental triggers (such as infections, tissue injury, and inflammation) that promote lymphocyte entry into tissues, activation of self-reactive lymphocytes, and tissue damage.
