Hypersensitivity type I
Download
Report
Transcript Hypersensitivity type I
آلرژی چیست؟
مکانیسم القاء آلرژی چگونه است؟
آلرژی غذایی چیست؟
مهمترین آلرژن های غذایی
ویژگیهای آلرژن های غذایی
تولرانس نسبت به مواد غذایی تابع چه عواملی است ؟
hypersensitivity type I
*Allergen
Activation of Th2
B cell activation
IgE
binding of IgE to Fc receptor
reexposure to Allergen
pathologic reactions
release of mediators
General features
Immediate hypersensitivity
با ورود آلرژن ،سلولهای B
آن راشناسایی وپس از فعال
شدن ،آنتی بادی IgEترشح
میکنند .
Mast cell activation
Factors involve in H.S type I
Allergene
Th2 cells
Mast and basophil cells
FcR-I
Mediators
Genetic predisposition
cytokines
Eosinophil and Basophil
اين سلولها داراي گيرنده هاي high
affinityبراي IgEبنام FCRمي
باشند
گرانولهايي سيتوپالسمي كه حاوي آنزيم
ها و ساير مدياتورهاي فارماكولوژيك
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,TNF-)
Mediators actions
Histamine= bronchoconstrictor,vascular
leak,intestinal hypermotility
PGD2=vasodilator and bronchoconstrictor ,
neut. Chemotaxis
LTC4=bronchoconstriction,inflammation
PAF=bronchoconstriction ,vasodilator,
inflammation
clinical and pathologic
manifestations of Type
increased vascular permeability
Vasodilation
smooth muscle contraction
local inflammation
Clinical and pathologic features
Hay fever(allergic rhinitis)
Increased peristalsis
Bronchial asthma
Anaphylaxis
Wheal and Flare reaction
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.
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
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.
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.
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
IgE-mediated classic food allergic reactions are
those that are:
immediate
reproducible
and readily diagnosed by detection of food-specific
IgE
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.