Hypersensitivity type I

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Type type I hypersensitivity
hypersensitivity type I

• Allergen Activation of Th2 B
  cell activation IgE binding of IgE
  to Fc receptor
• reexposure to Allergen release of
  mediators
• pathologic reactions
  

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General features
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Immediate hypersensitivity

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  ???? ??? ? ???? ???? IgE ???? ?????? .

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Mast cell activation
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Factors involve in H.S type I

• Allergene
• Th2 cells
• Mast and basophil cells
• Fc?R-I
• Mediators
• Genetic predisposition
• cytokines

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Eosinophil and Basophil

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  IgE ???? FC?R ?? ?????
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Mast cell activation

• Rapid release of granule contents
  (degranulation)such as Histamine,tryptase,
  chymase,proteoglycans(heparin )
• Synthesis and secretion of lipid
  mediators(prostaglandines ,Leukotrienes)
• Synthesis and secretion of cytokines(IL-3,4,5,6,TN
  F-?)

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Mediators actions

• Histamine bronchoconstrictor,vascular
  leak,intestinal hypermotility
• PGD2vasodilator and bronchoconstrictor , neut.
  Chemotaxis
• LTC4bronchoconstriction,inflammation
• PAFbronchoconstriction ,vasodilator,
• inflammation

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clinical and pathologic manifestations of Type

• increased vascular permeability
• Vasodilation
• smooth muscle contraction
• local inflammation

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??Clinical and pathologic features

• Hay fever(allergic rhinitis)
• Increased peristalsis
• Bronchial asthma
• Anaphylaxis

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Wheal and Flare reaction
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Food Allergy
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Introduction to food allergies

• Actually, only about 2-10 of adults and
  children have clinically proven true allergic
  reactions to food.
• food intolerance or other adverse reactions to
  food
• A true food allergy
• People who have food allergies must identify and
  prevent them because, although usually mild and
  not severe, these reactions can cause devastating
  illness and, in rare instances, can be fatal.

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• Food intolerance refers to an adverse physiologic
  response to a food and may be due to inherent
  properties of the food
• a)toxic contaminant
• b)pharmacologic active component
• or to characteristics of the host
• a)metabolic disorders
• b)idiosyncratic responses
• c)Psychological disorder
• they may not be reproducible
• they are often dose dependent.
• Food allergy refers to an abnormal immunologic
  response to a
• food that occurs in a susceptible host.
• a)These reactions are reproducible each time
  the food is ingested
• b) they are often not dose dependent

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• Histamine toxicity Some natural substances (for
  example, histamine) in foods can cause reactions
  resembling allergy. Histamine can reach high
  levels in cheese, some wines, and certain fish
• Food additives Another type of food intolerance
  is an adverse reaction to certain compounds that
  are added to food to enhance taste, provide
  color, or protect against the growth of
  microorganisms.
• The compounds most frequently tied to adverse
  reactions that can be confused with food allergy
  are
• yellow dye number 5(tartrazine)
• monosodium glutamate (MSG)
• and sulfites.

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What are the most common food allergies?

• In adults, the most common foods that cause
  allergic reactions are shellfish, such as shrimp,
  lobster, nuts from trees, such as walnuts fish
  eggs and peanuts.
• In children, the pattern is somewhat different
  from adults, and the most common foods that cause
  allergic reactions are eggs, milk, peanuts, and
  fruits, particularly tomatoes and strawberries.

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Food allergy varieties

• Based on the immunological mechanism involved,
• food allergies may be further classified in
• a)IgE-mediated
• b) Cell mediated
• c) mixed IgE mediated-cell mediated when both IgE
  and immune cells are involved in the reaction

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• IgE-mediated classic food allergic reactions are
  those that are
• immediate
• reproducible
• and readily diagnosed by detection of
  food-specific IgE

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Characteristics common to major food allergens
are that

• they are water-soluble glycoproteins, are 10 to
  70kD in size
• and are relatively stable to heat, acid, and
  proteases.
• Frequent exposure
• High glycosylation
• In addition, the presence of immunostimulatory
  factors in the food may also contribute to such
  sensitization.
• However, the biochemical characteristics of a
  food allergen cannot explain alone , as only a
  minority of patient exposed to it develop allergy.