HYPERSENSITIVITY

HYPERSENSITIVITY

1. type 1

   • immediate @ anaphylactic
   • localized & systemic
   • allergy
   • 2 part mechanisms
     • sensitization upon initial exposure
     • degranulation of sensitized cells
       • reexposures -> allergen bind to allergen-specific -> cross linkage -> sensitized cell activation -> synthesis of newly formed mediators
         • may lead to ANAPHYLAXIS REACTION ( shock )

2. type 2

   • cytotoxic h/s
   • IgM / IgG react with antigens on cell/tissue
   • 3 syndromes
     • blood transfusion reaction
       • blood A, B, AB, O
       • differ on surface antigen of RBC
       • ntigen bind to transfused RBC -> complement pathway -> lysis of blood cells
     • haemolysis diseases
       • due to rhesus antigen of RBC
       • Rh(+)- with rh antigen
       • Rh(-) - no rh antigen
       • Rhogam - anti-Rh serum
     • Drug-induced hypersensitivity
       • drugs -> complex formed -> foreign to host -> antibodies produced -> complenet lysis or phagocytosis
       • destruction of platelets - inhibit ability clotting blood correctly

3. type 3

   • immune complex h/s
     • complex escape phagocytosis and complement -> circulate -> trap in organ, joint and tissue -> trigger mast cells to degranulate -> damage the site
   • 1. localized immune complex disease
   • 2. systematic immune complex disease

4. type 4

   • cell mediated type h/s
   • DTH responses -> Th1 secrete cytokinesis -> recruited cells secrete lytic enzymes -> damage to tissue
   • occured in response to small chemical encountered with skin

5. contact hypersensitivity

   • too small to stimulate immune response in free form
   • CH response : similar to DTH

6. Autoimmune Disease

   • immune response againts one or more self antigen
   • Classifications
     • 1. Organ specific AD
     • 2. Non-organ specific AD
   • it happens by :
     • 1. complement-mediated lysis
     • 2. Opsonisation
     • 3. Inhibition of receptor function
     • 4. Stimulation of receptors
     • 5. Blockage of biological function
     • 6. Deposition of immune complexes
   • Causes of AD
     • 1. Genetic
     • 2. Environmental
       • a) infectious agent
       • b) drugs
       • c) toxins & pollutants
     • 3. Loss of immunotolerance
       • caused by :
         • a) production of high-affinity autoantibody
         • b) Generation of autoreactive T cells
         • c) Autoantibodies produced by autoreactive B cells in absence of T cells