Autoimmunity, definition , Autoimmune disorders dorders

Autoimmunity and autoimmune disorders

1. Autoimmunity

2. Definition 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. 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 tissues and antigens.

3. The body is able to distinguish self from non self antigens by the following mechanisms Clonal elimination-during embryonic development T cells maturing in the thymus acquire the ability to distinguish self from non self.These T cells are eliminated by apoptosis. Clonal anergy -T cells which have acquired the ability to distinguish self from non self are not eliminated but become inactive and non responsive. Suppressor T cells-here tolerance is achieved by a population of specific suppressor T cells which donot allow the antigen responsive cells to proliferate and differentiate .

4. Pathogenesis Usually autoimmunity is prevented by 3 major processes Sequestration of auto antigens and their unavailability for autoimmune response Generation and maintenance of tolerance or anergy by T and B lymphocytes Regulatory mechanisms limiting response by immune system. The mechanisms by which immune tolerance is broken-autoimmunity 1.Immunological factors- Polyclonal activation of T cells Generation of self reacting B cell clones Decreased T suppressor and increased T helper cell activity Sequestrated antigen released from tissue

5. 2.Genetic factors Evidences of genetic factors Increased expression of Class II HLA antigen Familial incidence of some forms of autoimmune disorders Higher incidence of autoimmune disorders in twins 3.Microbial factors Infection with microorganisms like virus (EBV),bacteria(Streptococci, Klebsiella )

6. Criteria for diagnosis Lab evidence Presence and documentation of autoantibodies Demonstration of T cell reactivity to self antigen Lymphocytic infiltrate in lesion Production of cytokines by helper T cells Evidence to support production of pathological lesion in tissues by transplacental Transmission Transfer of autoimmune disease to experimental animal by administrating autoantibodies Clinical evidence Association of other autoimmune disorder Improved response to immunosuppressive agent Family history.

7. Types Organ Specific diseases Autoamtibodies formed react specifically against an organ and cause chronic inflammatory response. Egs-thyroid,pancreatic islet of Langerhans,adrenal cortex Systemic disease Autoantibodies react with antigens in many tissues and cause systemic disease

8. Organ specific disease Endocrine Glands Hashimotos thyroiditis Graves disease Type 1 DM Idiopathic Addison’s disease Alimentary tract Autoimmune atrophic gastritis Ulcerative colitis Crohns disease Blood cells Autoimmune hemolytic anaemia Autoimmune thrombocytopenia Pernicious anemia

9. Others Myasthenia gravis Autoimmune orchitis Autoimmune encephalomyelitis Goodpastures syndrome Primary biliary cirrhosis Lupoid hepatitis

10. Sytemic Disease Systemic lupus erythematosus Rheumatoid arthritis Scleroderma Inflammatory myopathy( polymyositis,dermatomyositis ) Polyarteritis nodosa Sjogrens syndrome Wegeners granulomatosis

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