Hypersensitivity reactions (Immunological approach)

• Hypersensitivity Reactions


  Immune response that is excessive or aberrant, causing tissue damage and disease
• Immune response is essential for protection of body and maintenance of health (homeostasis)
• Immune responses can sometimes go inappropriate and cause tissue damage and disease
• Hypersensitivity


  A reflection of excessive or aberrant immune responses
• Hypersensitivity diseases


  Disorders that are caused by immune responses
• Causes of Hypersensitivity


  • Responses to foreign antigens => Tissue Injury
  • Failure of Self-Tolerance => Responses to self-antigens => Autoimmunity
• Types of Hypersensitivity


  • Type I – Immediate
  • Type II – Antibody-mediated (Cytotoxic)
  • Type III – Immune Complex
  • Type IV – Delayed Type
• Type I - Immediate Hypersensitivity

  • Rapid generalized immunologic reaction after exposure to certain antigens in a sensitized person
  • IgE antibody and mast cell-mediated vascular and smooth muscle reaction, followed by inflammation
  • Occurs in some individuals after exposure to certain foreign antigens which they have been exposed previously
  • ATOPIC=> Individuals with a strong tendency to develop these reactions
• Immediate Hypersensitivity Sequence of Events

  1. Production of antibodies in response to an antigen

  2. Binding of IgE to Fc receptors of mast cells

  3. Cross-linking of the bound IgE by reintroduced antigen

  4. Release of mast cell mediators
• Allergens


  Antigens that elicit immediate hypersensitivity reactions
• Immediate Hypersensitivity Clinical Syndromes

  • Allergic rhinitis and sinusitis (Hay fever)
  • Food allergies
  • Bronchial asthma
  • Anaphylaxis
• Anaphylaxis


  An acute, potentially life-threatening hypersensitivity reaction, involving the release of mediators from mast cells, basophils and recruited inflammatory cells
• Anaphylaxis Signs and Symptoms

  • Respiratory or airway compromise from swelling or wheezing
  • Hypotension or cardiovascular collapse
  • Diffuse cutaneous findings (urticaria, angioedema, +/-erythroderma)
• Type I Hypersensitivity Treatment

  • Antihistaminic agents
  • Bronchodilators
  • Corticosteroids
  • Epinephrine
  • Hyposensitization (Building up of IgG "blocking" antibodies)
• Type II Hypersensitivity


  Antibodies against cells or extracellular matrix components may deposit in any tissue that express the relevant target antigen
• Type III Hypersensitivity


  Immune complexes tend to deposit in blood vessels at sites of turbulence (branches of vessels) or high pressure (kidney glomeruli and synovium)
• Human antibody-mediated diseases


  • Autoimmune hemolytic anemia
  • Autoimmune (idiopathic) thrombocytopenic purpura
  • Pemphigus vulgaris
  • Goodpasture's syndrome
  • Acute rheumatic fever
  • Myasthenia Gravis
  • Graves' disease (hyperthyroidism)
  • Pernicious anemia
• Human immune complex diseases


  • Systemic lupus erythematosus
  • Polyartheritis nodosa
  • Post-streptococcal glomerulonephritis
• Type IV Delayed Type Hypersensitivity

  • Most T cell-mediated hypersensitivity diseases probably due to autoimmunity
  • The autoimmune reactions are usually directed against cellular antigens with restricted tissue distribution
  • Therefore T cell-mediated autoimmune diseases tend to be limited to a few organs and are not systemic
  • It can be also an entirely normal T cell responses to microbes, such as in tuberculosis
• T cell-mediated diseases


  • Insulin-dependent (type 1) diabetes mellitus
  • Multiple Sclerosis
  • Rheumatoid arthritis
  • Inflammatory bowel disease
• Tuberculosis skin test - PPD (Purified Protein Derivatives) is an example of Type IV Delayed Type Hypersensitivity to Tuberculosis Antigens
• Hypersensitivity Reactions


  Immune response that is excessive or aberrant, causing tissue damage and disease
• Immune response is essential for protection of body and maintenance of health (homeostasis)
• Immune responses can sometimes go inappropriate and cause tissue damage and disease
• Hypersensitivity


  A reflection of excessive or aberrant immune responses
• Hypersensitivity diseases


  Disorders that are caused by immune responses
• Causes of Hypersensitivity


  • Responses to foreign antigens => Tissue Injury
  • Failure of Self-Tolerance => Responses to self-antigens => Autoimmunity
• Types of Hypersensitivity


  • Type I – Immediate
  • Type II – Antibody-mediated (Cytotoxic)
  • Type III – Immune Complex
  • Type IV – Delayed Type
• Type I - Immediate Hypersensitivity

  • Rapid generalized immunologic reaction after exposure to certain antigens in a sensitized person
  • IgE antibody and mast cell-mediated vascular and smooth muscle reaction, followed by inflammation
  • Occurs in some individuals after exposure to certain foreign antigens which they have been exposed previously
  • ATOPIC=> Individuals with a strong tendency to develop these reactions
• Immediate Hypersensitivity Sequence of Events

  1. Production of antibodies in response to an antigen

  2. Binding of IgE to Fc receptors of mast cells

  3. Cross-linking of the bound IgE by reintroduced antigen

  4. Release of mast cell mediators
• Allergens


  Antigens that elicit immediate hypersensitivity reactions
• Immediate Hypersensitivity Clinical Syndromes

  • Allergic rhinitis and sinusitis (Hay fever)
  • Food allergies
  • Bronchial asthma
  • Anaphylaxis
• Anaphylaxis


  An acute, potentially life-threatening hypersensitivity reaction, involving the release of mediators from mast cells, basophils and recruited inflammatory cells
• Anaphylaxis Signs and Symptoms

  • Respiratory or airway compromise from swelling or wheezing
  • Hypotension or cardiovascular collapse
  • Diffuse cutaneous findings (urticaria, angioedema, +/-erythroderma)
• Type I Hypersensitivity Treatment

  • Antihistaminic agents
  • Bronchodilators
  • Corticosteroids
  • Epinephrine
  • Hyposensitization (Building up of IgG "blocking" antibodies)
• Type II Hypersensitivity


  Antibodies against cells or extracellular matrix components may deposit in any tissue that express the relevant target antigen
• Type III Hypersensitivity


  Immune complexes tend to deposit in blood vessels at sites of turbulence (branches of vessels) or high pressure (kidney glomeruli and synovium)
• Human antibody-mediated diseases


  • Autoimmune hemolytic anemia
  • Autoimmune (idiopathic) thrombocytopenic purpura
  • Pemphigus vulgaris
  • Goodpasture's syndrome
  • Acute rheumatic fever
  • Myasthenia Gravis
  • Graves' disease (hyperthyroidism)
  • Pernicious anemia
• Human immune complex diseases


  • Systemic lupus erythematosus
  • Polyartheritis nodosa
  • Post-streptococcal glomerulonephritis
• Type IV Delayed Type Hypersensitivity

  • Most T cell-mediated hypersensitivity diseases probably due to autoimmunity
  • The autoimmune reactions are usually directed against cellular antigens with restricted tissue distribution
  • Therefore T cell-mediated autoimmune diseases tend to be limited to a few organs and are not systemic
  • It can be also an entirely normal T cell responses to microbes, such as in tuberculosis