HYPERSENSITIVITYHypersensitivity refers to undesirable reactions produced by the normal immune system, including allergies andautoimmunityThese reactions may be damaging, uncomfortable, or occasionally fatal.TYPE OF HYPERSENSITIVITYBut in this video we are going to see only about Type 1 and Type 2TYPE I. IMMEDIATE OR ANAPHYLACTIC HYPERSENSITIVITY• Type I hypersensitivity is also known as immediate or anaphylactic hypersensitivity.• The reaction may involve skin (urticariaand eczema), eyes (conjunctivitis), nasopharynx (rhinorrhea, rhinitis), bronchopulmonary tissues (asthma) and gastrointestinal tract (gastroenteritis).• The reaction may cause a range of symptoms from minor inconvenience to death.The reaction usually takes 15 - 30 minutes from the time of exposure to the antigen, although sometimes it may have a delayed onset (10 - 12 hours).• Mediated by IgE antibody to specific antigens• The primary cellular component in this hypersensitivity is the mast cell or basophil.The reaction is amplified and/or modified by platelets, neutrophils and eosinophils.Mast cells stimulated and release histamine.CAUSESALLERGEN:Allergens are nonparasite antigens that can stimulate a type I hypersensitivity response.COMMON ALLERGENSASSOCIATED WITH TYPE IHYPERSENSITIVITYProteins,Foods,Foreign MECHANISM:Initial introduction of antigen produces an antibody response. More specifically, the type of antigen and the way in which it is administered induce the synthesis of IgE antibody in particular.Immunoglobulin IgE binds very specifically to receptors on the surface of mast cells, which remain circulating.TREATMENT• Drugs.Non-steroidal anti-inflammatories Antihistamines block histamine receptors.SteroidsTheophylline OR epinephrine -prolongs or increases CAMP levels in mast cells which inhibits degranulation.ImmunotherapyDesensitization (hyposensitization) also known as allergy shots.Repeated injections of allergen to reduce the IgE on Mast cells and produce IgG.TYPE II HYPERSENSITIVITYType II hypersensitivity is also known as cytotoxic hypersensitivity and may affect a variety of organs and tissues.• The antigens are normally endogenous, although exogenous chemicals (haptens) which can attach to cell membranes can also lead to type II hypersensitivity.Drug-induced hemolytic anemia,granulocytopenia and thrombocytopeniaare such examples. Pencillin allergy alsobelong to this class.DIAGNOSIS• Diagnostic tests include detection of circulating antibody against the tissues involved and the presence of antibody and complement in the lesion (biopsy) by immunofluorescence.• The staining pattern is normally smooth and linear, such as that seen in Goodpasture's nephritis.