آلرژی چیست؟مکانیسم القاء آلرژی چگونه است؟آلرژی غذایی چیست؟مهمترین آلرژن های غذاییویژگیهای آلرژن های غذاییتولرانس, نسبت به مواد غذایی تابع چه عواملی است ؟

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

General features

Immediate hypersensitivity ، با ورود آلرژن

آن Bسلولهای راشناسایی وپس از

فعال شدن ، آنتی بادی IgE. ترشح میکنند

Mast cell activation

Factors involve in H.S type IAllergeneTh2 cellsMast and basophil cellsFcR-IMediatorsGenetic predispositioncytokines

Eosinophil and Basophil اين سلولها داراي گيرنده

براي high affinityهاي IgE بنام FCRمي باشند

گرانولهايي سيتوپالسمي كهحاوي آنزيم ها و ساير

مدياتورهاي فارماكولوژيك

Mast cell activationRapid 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 actionsHistamine=

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 permeabilityVasodilationsmooth muscle contractionlocal inflammation

Clinical and pathologic featuresHay fever(allergic rhinitis)Increased peristalsisBronchial asthmaAnaphylaxis

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 allergyPeople 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 fooda)toxic contaminantb)pharmacologic active componentor to characteristics of the hosta)metabolic disordersb)idiosyncratic responsesc)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 varietiesBased on the immunological mechanism

involved,food allergies may be further classified in :a)IgE-mediatedb) 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 exposureHigh glycosylationIn 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.