Hypersensitivity Or Allergy


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This Powerpoint Illustrates The Hypersensitivity Type-I Only
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Rania Hadi

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Hypersensitivity Or Allergy

  1. 1. Hypersensitivity Reaction or Allergy “Microbiology” By Rania Hadi Aden University-Faculty Of Dentistry
  2. 2. Content -Simple Introduction. -Hyper sensitivity or allergy type-I
  3. 3. Exaggerated immune response may lead to different forms of tissue damage: 1) An overactive immune response: produce more damage than it prevents e.g. hypersensitivity reactions and graft rejection 2) Failure of appropriate recognition: as in autoimmune diseases
  4. 4. Introduction We Have To Know That allergy is Abnormal And May Be Harmful To Human Body. Definition . So the hypersensitivity reaction is an abnormal and may be dangerous (damaging or sometimes fatal) from a normal immunity’s Response to the body’s tissues. Allergy Types Based on the mechanisms involved and time taken for the reaction ,There are 4 types of allergy *Type I and Type II are body-mediated, Reaction mediated by IgE *Type III is body-mediated as well ,but reaction mediated by IgG. *Type IV is cell-mediated.
  5. 5. Type [I] About: -This type is the most common one. -Called Immediate hypersensitivity and anaphylactic hypersensitivity as well. -This type doesn’t occur in all population. -symptoms of this type are called : anaphylaxis KEYS 1-Mast Cell A Large cell which contains granules or vesicles containing Mediators like Histamine Inside it ,and it’s role related to allergy . 2-Allergen : is a type of antigen that produces an abnormally immune response. 3-IgE : Is a specific one of the 5 antibodies which plays an essential role in allergy type-I,And it’s induced by this allergen, produced by B-cells.
  6. 6. On the surface of mast cell, there's a receptor called IgE receptor or (Fcε) receptor ε = epsilon This receptor receives the IgE for Binding on the surface of mast cell *Note The IgE Antibody Has 2 regions, one of them is called Fc region for binding to Fcε receptor on mast cell surface And the second region is for binding with the Allergen or antigen. (See the next slide below)
  7. 7. IgE Structure
  8. 8. Pathogenic Mechanism 1-Exporsure for 1st time : An allergen invades the human body, and this can be occurred by digestion(Food),inhalation and injection. Induction of formation of IgE By B-cell ,which binds to the mast cell by its Fc ,called sensitization, and innate immunity play its role to eject the pathogen. 2-Reexporsure for 2nd time: of same allergen again, Allergen cross links IgE on mast cell surface and trigger degranulation of mast cell occurs(release of mediators)in human tissues Cross-linking meaning : Side by side (lateral) linking in which two or more adjacent molecules of a polymer join to form a bigger molecule. It’s important in this type
  9. 9. Reexporsure
  10. 10. Mechanism [Con’t] *What are the mediator that released from mast cell? Mediator are soluble substances which cause manifestation of disease. Calcium and cyclic nucleotide play role in release of these mediators Note : NO Single mediator accounts or causes for all the allergy Type-I Manifestation or symptoms. *There are 3 classes of mediators derived from mast cell : 1-Preformed or primary Mediators 2-Newly sensitized ,synthesized or Secondary Mediators 3-cytokines and chemokines.
  11. 11. Type-I Effects The Clinical Manifestations Occurs Depends In Large Part Of The Mast Cells Bearing The IgE Specific For The Allergen For example patients who respond to an allergen with urticaria have the allergen-specific IgE on mast cell in the skin, whereas those who respond with rhinitis have the allergen-specific IgE on mast cell in the nose. -the most sever form of type-I and considered as life-threating is Systemic Anaphylaxis (branchoconstriction+hypotension)
  12. 12. [Con’t] Effects of these substances when released 1-Histamine: vasodilation, increased capillary permeability & smooth-muscle contraction. Clinically : rhinitis (hay fever) urticaria and angioedema can occur and bronchospasm.
  13. 13. [Con’t] 2-Release of Leukotrienes: the principal mediator in the bronchoconstriction of asthma ,increased vascular permeability and smooth muscle constriction occur
  14. 14. [Con’t] 3-Eosinophil Chemotactic Factor Anaphylaxis (ECF-A) -is a tetra peptide -when released attracts Eosinophil's -may reduce the severity of allergy type-I -The role in Type-I is Uncertain -they release histaminase and arylsulfatase which degrade 2 important mediators, Histamine and SRS-A (slow-reacting substances of anaphylaxis)respectively
  15. 15. [Con’t] 4-Serotonin(hydroxytryptamine) When released causes increased vascular permeabiltty,capillary dilation and smooth muscles contraction. 5-prostaglandin and thromboxanes -Prostaglandin causes dilation and increased permeability and bronchoconstriction -Thromboxanes aggregate platelets
  16. 16. Manifestation of anaphylaxis Vary among the species Because mediators are released in different amounts and different rates, and tissues vary in their sensitivity to them. For Example :the respiratory tract (bronchospasm and laryngeal edema) is principle shock organ in Human But the Liver play that role in Dogs Don’t be confused B/W Anaphylactic Reactions and Anaphylactiod Reactions. -Anaphylactiod Reactions appear Clinically similar to the anaphylactic reactions -not IgE-Mediated -in this reaction usually the initiating agents induce the degranulation of mast cell without IgE involvement.
  17. 17. Atopy(Atopic Disorders) Atopy is the genetic predisposition of an individual to produce high quantities of IgE in response to allergens in the environment (pollens, house dust mites, moulds, cat dander, foods etc). Heredity is very important in atopy. The terms atopy and allergy are often used interchangeably but are different: *Atopy is an exaggerated IgE-mediated immune response; all atopic disorders are type I hypersensitivity disorders. *Allergy is any exaggerated immune response to a foreign antigen regardless of mechanism.
  18. 18. Laboratory Diagnosis Allergy-I Skin Test Serum Test
  19. 19. 1-Skin (Cutaneous)Test : Called Skin Prick Test (SPT) Routine diagnosis in diseases (atopic or anaphylactic). A single drop of concentrated aqueous allergen extract placed on the skin which is then pricked lightly with a needle point at the center of the drop. After 20 minutes the reaction is graded and recorded 2-Serum Test : for detecting the levels of IgE
  20. 20. Treatment & Prevention -Epinephrine -Antihistamines -corticosteriods -cromolyn sodium