Food Allergies: What

1
Food AllergiesWhats New in Clinical,
Community, School and Food Service Applications

• Janice M. Joneja, Ph.D., RD
• 2006

2
Food Allergy in the Past 5 Years

• Nearly 4 of North Americans have food allergies,
  many more than recorded in the past
• Incidence of food allergy much higher in children
  (gt8) than adults (lt2)
• Prevalence of peanut allergy doubled in American
  children younger than 5 years of age in the past
  5 years

3
Food Allergy in the Past 5 Years

• Incidence of food intolerances estimated to be up
  to 50 of the population, but accurate figures
  are not available because of the lack of
  appropriate tests
• Incidence of food intolerances much higher in
  adults than in children
• Many food allergens have been characterized at
  the molecular level, leading to increased
  understanding of the causes of many allergic
  disorders

4
Food Allergy Food Intolerance

• Food Intolerance
• A generic term
• describing an abnormal
• physiological response
• to an ingested food or food additive which is not
  a result of a response of the immune system
• Is dose-dependent

• Food Allergy
• A response of the immune system to an ingested
• food or food additive
• Is not dose-dependent

5
Management of Food Allergies and Intolerances

• Management of food sensitivities consists of
• Accurate identification of the food causing the
  problem
• Educating clients on how to avoid relevant
  allergens and intolerance triggers in foods
• Formulating appropriate diets to avoid the
  culprit foods and replacing them with foods of
  equivalent nutritional value
• Educating parents in measures to avoid
  sensitization of their at-risk babies

6
The Allergic Diathesis
Atopic dermatitis (Eczema)

• .

Sleep deprivation
Gastrointestinal symptoms
Irritability
Food Allergy
Mental fogginess
Fatigue
In infants failure to thrive
Allergic rhinoconjunctivitis (hay fever)
Asthma (cough wheeze)
Anaphylaxis
7
Allergy is a Response of the Immune System

• Our immune systems are designed to protect the
  body from invasion by foreign materials
• T cell lymphocytes detect foreign proteins
  (antigens) in any form
• T cells then trigger a series of immunological
  reactions, mediated by cytokines

8
Antigen Recognition

• The first stage of an immune response is
  recognition of a foreign antigen (protein or
  glycoprotein)
• T cell lymphocytes are the controllers of the
  immune response
• T helper cells (CD4 subclass) (Th) identify the
  foreign protein as a potential threat

9
Education of the Immune System

• All foods contain proteins derived from plants
  and animals all of which are foreign to the
  human body
• In order for food to be absorbed, metabolized,
  and utilized by the body, the immune system needs
  to be educated that the foreign material is
  safe
• This involves a complex series of immunological
  reactions

10
Immune System of the Digestive Tract

• Immune system of the digestive tract is unique
  named the gut-associated lymphoid tissue (GALT)
• Recent evidence suggests that the most important
  cells in the initiation of the recognition
  process are the dendritic cells in the intestinal
  mucosa
• They take up dietary proteins and transport them
  to the mesenteric lymph nodes (MLN)
• Differentiation of the T cells takes place in the
  MLN

11
Oral Tolerance

• In most cases this results in education of the
  T cells to not respond to that food protein when
  it enters via the oral route called oral
  tolerance
• Contrasts with the active immune responses needed
  to protect the gut against continual bombardment
  by invading pathogens and their products (toxins,
  etc)
• Also contrasts with the reduced responsiveness to
  the millions of microorganisms that are permanent
  residents of the large bowel
• T cells involved in these processes are
  designated Treg

12
T cells involved in Oral Tolerance

• T cell response depends on the type of T helper
  cell that is activated
• Latest research indicates that T cells that
  produce a cytokine called TGF-? are important in
  inducing oral tolerance
• Sometimes called Th3 cells
• T cells that produce IL-10 may also be involved
  in tolerance
• These also regulate immune response to resident
  microflora, preventing the usual immune
  inflammatory response to microorganisms

___________________ Strobel and Mowat 2006
13
T-helper Cell Subclasses

• There are two subclasses of T-helper cells
• Type 1 Th1
• Type 2 Th2
• Cytokines (the control chemicals of the immune
  system) are released
• Each subclass produces a different set of
  cytokines
• The types of cytokines generated determine the
  resulting immune response

14
Role of T-helper Cell Subtypes

• Th1 triggers the protective response to a
  pathogen such as a virus or bacterium
• IgM, IgG, IgA antibodies are produced
• Th2 is responsible for the IgE-mediated
  hypersensitivity reaction (allergy)
• IgE antibodies are produced

15
Allergic Sensitization

• Cytokines associated with Th1 (protective)
  response are predominantly
• INF-?
• IL-2
• Cytokines associated with allergic (Th2) response
  are predominantly
• IL-4
• IL-13

16
Th1 Th2 Interactions
Factors promoting
Th2 - Parasite infestations - Immature immune
system
Th1 - Bacterial and viral infections -
Maturation of the immune system
17
Th1 Th2 Interactions
Factors promoting
Th2 - Parasite infestations - Immature immune
system - Sensitization to antigen
Th1 - Bacterial and viral infections -
Maturation of the immune system - Antigen
tolerance

• Contributing factors
• - Genetic inheritance
• - Early exposure to allergen
• Increased antigen uptake
• leaky gut

18
Conditions That May Induce Th2 Response

• Inherited allergic potential
• Immaturity of the immune system
• Inflammatory conditions in the gut that interfere
  with the normal antigen processing pathway
• Immaturity of the digestive mucosa leading to
  hyperpermeability (leaky gut)
• Increased uptake of antigens

19
Th1 Th2 Interactions

• Under certain circumstances (eg eczema) Th2
  cytokines suppress Th1 cell activity
• This causes a decrease in the level of immune
  protection against microorganisms
• As a result, infection by normally harmless skin
  bacteria can occur

20
Th1 Th2 Interactions

• In contrast, Th1 activity may suppress Th2
  response
• Infection with some common childhood illnesses
  may suppress allergy - the hygiene theory
• Certain microorganisms in the large bowel (the
  resident microflora) can influence the Th1/Th2
  balance role for probiotics?
• Latest research indicates a possible role for a
  new cytokine IL-18 in Th1/Th2 balance

____________________ Cebeci et al August 2006
21
IgE-Mediated hypersensitivity Intracellular
Granules are Released
22
Many Inflammatory Chemicals are Released in the
Allergic Reaction

• Preformed
• Histamine
• Enzymes
• Chemo-attractants
• Newly formed
• Prostaglandins
• Leukotrienes
• Each chemical has a different effect on tissues
• The allergic response is the combined effect of
  them all

23
Action of Inflammatory Mediators on Tissues?
Histamine ?

• Vasodilation blood vessels widen
• Swelling of tissues
• Increased vascular permeability blood vessels
  become leaky
• angioedema (swelling)
• rhinitis (stuffy nose)
• rhinorrhea (runny nose)
• urticaria (hives)
• otitis media (earache)
• Itching
• Flushing
• Reddening
• Antidote Antihistamines
• Block receptors for histamine on reactive cells

24
Priority Food Allergens In Canada

• Peanuts
• Tree nuts (almonds, Brazil nuts, cashews,
  hazelnuts (filberts), macadamia nuts, pecans,
  pinenuts, pistachios, walnuts)
• Sesame seeds
• Milk
• Eggs
• Fish
• Shellfish (e.g. clams, mussels, oysters, scallops
  and crustaceans (e.g. crab, crayfish, lobster,
  shrimp) )
• Soy
• Wheat
• Sulphites
• These Priority Allergens account for more than
  95 of severe adverse reactions related to food
  allergens

25
Additional Factors Involved in Symptoms of Food
Sensitivity

• Increased permeability of the digestive tract
• (leaky gut)
• Inflammation
• Infection
• Allergy
• Autoimmune disease
• Other diseases
• Immaturity (in infants)
• Alcohol consumption
• Physical exertion
• Exercise-induced anaphylaxis

26
Additional Factors Involved in Symptoms of Food
Sensitivity

• Stress
• Eating several different allergenic foods at the
  same time
• Other allergies occurring at the same time (e.g.
  hay fever, asthma)

27
Classification of Food Allergens

• Class 1
• Direct sensitization via the gastrointestinal
  tract after ingestion
• Water-soluble proteins or glycoproteins
• Stable to heat, proteases, and acid
• Many are lipid transfer proteins
• Class 2
• Indirect sensitization by inhalation of air-borne
  allergen
• Cross-reaction to foods containing structurally
  identical proteins
• Heat labile
• Many are pathogenesis-related proteins

____________ Sampson 2003
28
Oral Allergy Syndrome(OAS)

• OAS refers to clinical symptoms in the mucosa of
  the mouth and throat that
• Result from direct contact with a food allergen
• In an individual who also exhibits allergy to
  inhaled allergens.
• Usually pollens (pollinosis) are the primary
  allergens
• Pollens usually trigger rhinitis or asthma
• Occurs most frequently in adults

29
Oral Allergy SyndromeCharacteristics

• Inhaled pollen allergens sensitize tissues of the
  upper respiratory tract
• Tissues of the respiratory tract are adjacent to
  oral tissues, and the mucosa is continuous
• Sensitization of one leads to sensitization of
  the other
• OAS symptoms are mild in contrast to primary food
  allergens and occur only in and around the mouth
  and in the throat

30
Oral Allergy Syndrome

• The foods cause symptoms in the oral cavity and
  local tissues immediately on contact
• Swelling
• Throat tightening
• Tingling
• Itching
• Blistering
• Foods most frequently associated with OAS are
  mainly fruits, a few vegetables, and nuts

31
Oral Allergy SyndromeAllergens

• Pollens and foods that cause OAS are usually
  botanically unrelated
• Occurs most frequently in persons allergic to
  birch and alder pollens
• Also occurs with allergy to
• Ragweed pollen
• Mugwort pollen
• Grass pollens

32
Oral Allergy SyndromeCross-reacting allergens

• Birch pollens with
• Apple
• Stone Fruits (Apricot, Peach, Nectarine, Plum,
  Cherry)
• Kiwi Fruit
• Orange - Peanut - Almond
• Melon - Hazelnut -
  Walnut
• Watermelon - Carrot - Anise
• Potato - Celery - Caraway seed
• Tomato - Parsnip
• Green pepper - Parsley
• Cumin - Beans
• Coriander - Peas
• Dill - Lentils
• Sunflower seed - Soy

33
Oral Allergy SyndromeCross-reacting allergens

• Ragweed pollen with
• Banana
• Cantaloupe
• Honeydew
• Watermelon
• Other Melons
• Zucchini (Courgette)
• Cucumber

34
Expression of OAS Symptoms

• Oral reactivity to the food significantly
  decreases when food is cooked
• Reactivity of the antigen depends on ripeness
• Antigen becomes more potent as the plant material
  ages
• People differ in the foods which trigger OAS,
  even when they are allergic to the cross-reacting
  pollens
• Foods contain an antigen that is structurally
  similar to the allergenic pollen, but not all
  people will develop OAS to all foods having that
  antigen

35
Identification of Foods Responsible for OAS
Symptoms

• Skin tests will identify the allergenic plant
  pollen
• Skin testing has not been successful in
  identifying persons who react to cross-reacting
  food antigens
• Plant antigens are unstable and do not survive
  the process of antigen preparation
• Crushing plant material leads to release of
  phenols and degradative enzymes
• Prick prick technique are more reliable than
  standard skin tests
• Lancet is inserted in raw fruit or vegetable,
  withdrawn and then used to prick the persons skin

36
Latex-Fruit Syndrome

• Allergy to latex often starts as
• Contact allergy to a latex protein, usually
  through
• Abraded (non-intact) skin
• Mucous membrane
• Exposed tissue (e.g. during surgery)
• Inhalant allergy
• Inhaled powder from latex gloves

37
Latex AllergyCross-reacting allergens

• As antigen comes into contact with immune cells,
  repeated exposure leads to IgE mediated allergy
• Proteins in foods with the same structure as
  proteins in latex trigger the same IgE response
  when they are eaten
• In extreme cases can cause anaphylactic reaction

38
Latex AllergyRelated foods

• Examples of foods that have been shown to contain
  proteins similar in structure to latex
• Banana - Mango - Tomato
• Citrus Fruits - Melon - Celery
• Kiwi Fruit - Pineapple - Avocado
• Fig - Papaya - Tree Nuts
• Passion Fruit - Peach - Chestnut
• Grapes - Potato - Peanut

39
Common allergens in unrelated plant materials
Summary

• OAS and latex allergy are examples of conditions
  in which common antigens, expressed in
  botanically unrelated plants, are capable of
  eliciting a hypersensitivity reaction
• In practice, when a specific plant food elicits
  an allergic response, foods in the same botanic
  family rarely elicit allergy