Hypersensitive Reactions Allergies

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Hypersensitive ReactionsAllergies

• Hugh B. Fackrell

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Hypersensitive Reactions

• Assigned Reading
• Content Outline
• Performance Objectives
• Key terms
• Key Concepts
• Short Answer Questions

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Assigned Reading

• Chapter 17 pp 413-439
• Janis Kubys Immunology 3rd Ed

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Content Outline

• Gell Coombs Classification
• Type I Hypersensitivity IgE mediatiated
• Type II Hypersensitivity Antibody mediated
  cytotoxic
• Type III Hypersensitivity Complex mediated
  cytotoxic
• Type IV Hypersensitivity DTH mediated

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Type I Hypersensitivity IgE mediatiated

• Components
• Mechanisms
• Mediators
• Consequences
• Regulation
• Detection
• Therapy

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Components

• Allergens
• IgE
• Mast cells basophils
• IgE binding receptors

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House dust mite

• Mite fecal pellets are the major source of the
  allergen in house dust

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Cat Hair

• Major cause of allergies

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Pollen
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Type I Hypersensitivity
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Mechanisms

• receptor cross linkage
• Intracellular events

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Mechanism of Latex Allergy

• 3 step process
• sensitization
• Activation of mast cells
• Prolonged immune activity

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Sensitization to Latex Proteins

• Macrophage presents Ag to T cells
• T cells activate B cells via IL-4
• B cells become plasma cells make IgE
• IgE attaches to mast cell receptors

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Activation of Mast cells

• Allergen binds to IgE on mast cell
• Intracellular enzyme cascade
• immediate release of histamines cytokines
• Induction of intracellular lipids
• Prostoglandins, arachadonic acid

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Prolongation of Immune Activity
Chemical released by activated mast cells induce
basophils and other cells in the bloodstream to
migrate into the tissue. These cells sustain
immune activity which leads to tissue damage
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Allergen Activation
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Mediators

• histamine
• leukotriens prostoglandins
• cytokines

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Consequences

• systemic anaphylaxis
• localized anaphylaxis
• late phase reaction

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Atopic Eczema
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Anaphylatic Response to Bee venom
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Early vs late Response
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Detection
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Skin Patch Test
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Latex Questionaire

• Positive History
• RAST positive
• Avoid latex
• Rast Negative
• Patch tests Positive
• Identify allergen
• Patch tests Negative
• Treat dermatitis

• Negative History
• RAST positive
• Latex test positive
• Avoid latex
• latex test negative
• powder free gloves
• Rast negative
• Safe to use latex

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Therapy

• Hyposensitization
• IgG as blocking antibody
• repeated subcutaneous injections
• T cell anergy
• soluble antigens
• Antihistamines

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Drugs for Type I hypersenstivity

• Antihistamines blocks receptors
• Cromolyn sodium blocks Ca influx
• Theophylline
• inhibits phosphodiesterase
• cAMP kept high
• Epinephrine
• stimulates cAMP via beta adrenergic receptors
• Cortisone
• blocks conversion of histidine to histamine

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Performance Objectives
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Key Terms

• allergen, allergy, anaphylactic
  shock,anaphylaxis, anergy, atopy, basophils,
• contact sensitivity, degranulation, delayed type
  hypersensitivity,
• desenstization, granulomas, homocytotropic
  antibodies, hypersensitivity,

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• hyposensitivity, immediate hypersensitivity, late
  phase reaction, mast cells,
• sensitization, senstizing dose, shocking dose,
  systemic anaphlyaxis, triple response edema,
  erythema, wheal and flare,
• tubercles, tuberculin skine reaction,
  tuberculosis, Type I hypersensitivity,
• Type II hypersensitivity, Type II
  hypersensitivity, Type IV hypersensitivity.

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Key Concepts

• List the Gell Coombs classification for
  hypersensitivity reactions give examples of each
  type.
• Describe stimulatory hypersensitivity and give a
  specific example
• Discuss the difference between primary and
  secondary exposure to antigen in imunity and in
  hypersensitivity

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• Describe the structural and functional
  characteristics of IgE.
• Discuss the cytotropic nature of IgE
• Differentiate betweeen the cyclooxygenase and
  lipoxygenase pathways of mediator production

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• Describe the role of mast cells in immediate
  hypersensitivity reactions.
• Distinguish between release of preformed and
  newly formed mediators from mast cells and give
  examples of each type of mediator
• Discuss the hallmarks of delayed type
  hypersensitivity

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• Explain the mechanisms of Delayed Type
  Hypersensitivity induction and development
• Distinguish between different types of Delayed
  type hypersensitivity.
• Describe tuberculosis in terms of
  hypersensitivity reactions.

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Short Answer Questions
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• By derivation, what does allergy mean and what
  does hypersensitivity mean? Are they synonymous?
• The main difference between immediate and delayed
  types of hypersensivitiy is the time of
  appearance of the reactions. True/False? If
  false, name the main differences.
• What is the type II reaction described by Gell
  Cooombs? Does this reaction require complement?

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• Is there a tendency to immediate hypersenstivity
  reactions? Explain?
• Differentiate between antigen and allergen.
• What immune and nonimmune cells are involved in
  immediate hypersensivity?

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• What class of antibody in responsible for
  immediate hypersenstivity? Describe some
  structural and biological characteristics of this
  antibody?
• What do we mean by homocytotropic antibodies?
• Briefly describe the result of the interaction of
  IgE, with mast cells
• a) in the presence of allergen.
• b) in the absence of allergen.

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• What are the chemical mediators of immediate
  hypersentivity reactions?
• Some effector molecules of immediate
  hypersensitivity reactions are preformed
  mediators others are newly synthesized
  mediators. Distinguish between the two.
• Briefly describe the two pathways for the
  production of newly synthesized mediators.

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• How can you determine whether a person is
  allergic to a foreign protein?
• What is the triple response? Name two "in vitro"
  tests.
• What is the mechanism for desensitization for
  immediate hypersensitivities? Is this
  desensitization lifelong? If not speculate on the
  reasons. What are some other modes of treatment
  for immediate hypersensitivity?

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• Describe the differences between systemic
  anahylaxis and atopy?
• Are the mechanisms of cell-mediated immunity and
  DTH the same?
• Name the effector cells in DTH.
• What are some of the hallmarks of DTH reactions?

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• Describe contact sensitivity.
• How does contact sensitivity differ from the
  tuberculin skin reaction?
• What is the mechanism of the tuberculin skin
  test? If the test is positive what causes the
  induration (hardening) of the test site? What
  substances are used in this test?

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DONE!!!