IS-MIDTERM--hypersensitivity

• Hypersensitivity


  When an immune response results in exaggerated or inappropriate reaction harmful to the host
• Things associated with hypersensitivity

  • Allergens
  • Swollen
  • Itchiness
  • Redness
  • Basophils
  • Mast cells
  • Eosinophils
  • Histamines
  • Immunoglobulin - IgE
  • Inflammation
  • Tissue injury

  
• Hypersensitivity


  • Increased cells
  • Increased molecules
  • Increased immunoglobulins

  
• Two ways of hypersensitivity reactions

  • Immediate hypersensitivity - Antibody mediated
  • Delayed hypersensitivity - Cell mediated
• Allergens


  Nonparasitic antigens that can stimulate a type I hypersensitivity response

  
• Type I hypersensitivity


  Classic allergy, mediated by IgE attached to mast cells
• Type I hypersensitivity reaction


  1. Allergen inhaled/ingested

  2. Dendritic cell/APC phagocytizes allergen and presents to naive T cell

  3. Naive T cell activated, becomes helper cell

  4. Helper cells secrete IL-4 and 5 to activate B cells

  5. B cells differentiate into plasma cells that release IgE

  6. IgE binds to mast cells

  7. Re-exposure to allergen binds to IgE on mast cells

  8. Mast cells degranulate, release mediators like histamine

  9. Mediators cause immediate hypersensitivity reaction
• Allergens


  • Small 15-40,000 MW proteins
  • Specific protein components, often enzymes
  • Low dose required
  • Mucosal exposure
  • Promote Th2 immune response

  
• Atopy


  Genetic trait to have a predisposition for localized anaphylaxis, with higher IgE and eosinophils
• Sensitization to allergens


  1. Repeated exposure initiates immune response generating IgE

  2. Th2 cells provide IL-4 for IgE isotype switching

  3. IgE attaches to mast cells via Fc receptor, increasing IgE lifespan

  
• FcεR1


  High affinity IgE receptor found on mast cells, basophils, activated eosinophils
• Mediators of type I hypersensitivity

  • Histamine
  • Leukotrienes
  • Prostaglandins
• Localized anaphylaxis


  Target organ responds to direct contact with antigen, causing symptoms like vomiting, rash, rhinitis, wheezing
• Systemic anaphylaxis


  Systemic vasodilation and smooth muscle contraction leading to severe bronchiole constriction, edema, and shock
• Treatments for type I hypersensitivity

  • Non-steroidal anti-inflammatories
  • Antihistamines
  • Steroids
  • Theophylline or epinephrine
• Allergy testing methods


  • In vivo skin tests (prick, intradermal)
  • In vitro tests (total IgE, antigen-specific IgE, microarray)
• Type II hypersensitivity


  Cytotoxic hypersensitivity, where antibodies bind to the patient's own cell surfaces

  
• Mechanisms of type II hypersensitivity

  • Antibody-dependent, complement-mediated cytotoxic reactions
  • Antibody-dependent, cell-mediated cytotoxicity
  • Antireceptor antibodies

  
• Hemolytic disease of the newborn (HDN)

  Blood disorder in a fetus/newborn due to blood type mismatch between mother and baby
• Transfusion reaction


  Adverse consequences of incompatibility between patient and donor erythrocytes
• Type III hypersensitivity


  Immune complex reactions, caused by deposition of immune complexes in blood vessels and tissues

  
• Immune complex disease


  Occurs when neutrophils and macrophages are unable to phagocytize immune complexes, leading to inflammation

  
• Arthus reaction


  Local reaction with erythema and edema, peaking 3-8 hours after intradermal antigen injection
• Localized diseases from immune complex deposition

  • Arthritis
  • Glomerulonephritis
• Serum sickness


  Reaction from passive immunization with animal serum
• Autoimmune diseases


  • Systemic lupus erythematosus
  • Rheumatoid arthritis
• Type IV hypersensitivity


  Inflammatory reactions initiated by mononuclear leukocytes, mediated by T cells and macrophages

  
• Delayed-type hypersensitivity (DTH)


  1. Sensitization stage: Memory Th1 cells generated against DTH antigens

  2. Effector stage: Th1 cells activated, release cytokines causing inflammation and tissue damage

  3. Continued exposure can cause chronic inflammation and granuloma formation
• Contact dermatitis


  Allergic skin reaction to compounds like poison ivy, nickel, rubber, etc.
• Hypersensitivity pneumonitis


  Allergic disease of the lung parenchyma, characterized by inflammation of the alveoli and interstitial spaces
• Tuberculin type hypersensitivity


  Reaction to purified protein derivative (PPD) from Mycobacterium tuberculosis, read at 48-72 hours
• Type I Hypersensitivity involves anaphylactic reaction, IgE antibody, no complement, cell involved are mast cells, basophils, and granules that release histamine, there is cytokines, antibody mediated, immediate, the mechanism of tissue injury is allergic and anaphylactic reactions, and examples are anaphylaxis, hay fever, asthma, and food allergy
• Hypersensitivity


  When an immune response results in exaggerated or inappropriate reaction harmful to the host
• Things associated with hypersensitivity

  • Allergens
  • Swollen
  • Itchiness
  • Redness
  • Basophils
  • Mast cells
  • Eosinophils
  • Histamines
  • Immunoglobulin - IgE
  • Inflammation
  • Tissue injury

  
• Hypersensitivity

  • Increased cells
  • Increased molecules
  • Increased immunoglobulins

  
• Two ways of hypersensitivity reactions

  • Immediate hypersensitivity - Antibody mediated
  • Delayed hypersensitivity - Cell mediated

  
• Allergens


  Nonparasitic antigens that can stimulate a type I hypersensitivity response

  
• Type I hypersensitivity


  Classic allergy, mediated by IgE attached to mast cells
• Type I hypersensitivity reaction

  1. Allergen inhaled/ingested

  2. Dendritic cell/APC phagocytizes allergen and presents to naive T cell

  3. Naive T cell activated, becomes helper cell

  4. Helper cells secrete IL-4 and 5 to activate B cells

  5. B cells differentiate into plasma cells that release IgE

  6. IgE binds to mast cell receptors

  7. Re-exposure to allergen binds to IgE on mast cells

  8. Mast cell degranulation releases mediators like histamine

  9. Mediators cause immediate hypersensitivity reaction

  
• Allergens


  • Small 15-40,000 MW proteins
  • Specific protein components, often enzymes
  • Low dose required
  • Mucosal exposure
  • Promote Th2 immune response