Nutrition and Disease

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EXAM 1
EXAM 2
Average 33.3
Average 36.1
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Food Allergies
Lecture 24April 21, 2008Dr. QuadroFood
Science Department
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Prevalence of food allergy

• Experts agree that allergies in developed
  countries are becoming more common.
• In the U.S., food allergies afflict 2-2.5 adults
  and 6-8 children.
• 100-175 people in the U.S. die each year.
• Death generally result from anaphylactic shock,
  often to peanuts or tree nuts.
• More than 160 foods have been associated with
  allergic reactions.

CEN/January 7, 2002 page 21.
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What is food allergy?

• Food allergy is an inappropriate immune response
  to an otherwise harmless food.
• True food allergy involves several types of
  immunological responses.
• Food allergens are usually proteins.
• Some foods may contain haptens or haptens
  carrier.

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Understanding Immunological concepts

• Human body has many defense mechanisms to fight
  off infectious diseases and other toxic foreign
  substances.
• Strong healthy adult human can fight off most of
  infectious diseases.
• Ability to fight off disease can be modulated by
  genetics, age, race and lifestyles (diets,
  exercise and amount of sleep etc.)

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Basic Terminology

• Allergic reactions are Antigen-Antibody reactions
• Antigen a foreign substance
• Antibody a protein produced in response to an
  antigen that is capable of binding specifically
  to the antigen!
• Haptens - a small molecule that has the ability
  to combine with an Ab or a cell-surface receptor.

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• Human body has two categories of defense system
• Non specific defenses
• Physical barriers (skin and mucous membrane)
• Chemical barriers (saliva, mucus, gastric juices,
  etc)
• Cellular defenses (certain cells can eat
  invaders-phagocytes)
• Inflammation (reddening, swelling and temperature
  increase of the affected sites)
• Fever (elevated body temperature)
• Molecular defenses (interferons or complementary
  system etc.)
• Specific defenses or specific immunity
• Antibodies (many kinds of antibodies for many
  kinds of antigens)

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• Food allergies are related to specific defenses
  or specific immunity.
• Immune literary means free of burden.
• Actions of the immune system are triggered by
  antigens (foreign substances).
• Most antigens are large protein molecules Some
  antigens are polysaccharides and few are
  glycoproteins (carbohydrate and protein) or
  nucleo-proteins.

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Specific Immunity
Immunity
Ab Antibodies
Acquired
Innate (inborn) Genetic factors
Passive (Ready-made-Ab)
Active (own Ab)
Natural Maternal Ab
Artificial (Ab from Other sources)
Natural (Exposure to Foreign Agents)
Artificial (immunization)
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Antibodies (Immunoglobulins)

• Produces by B-linfocytes (bone marrow)
• Five classes of Immunoglobulins
• 1) IgG Main class of antibodies in blood-also
  from mother-to-child (20)
• 2) IgA Small amount in blood, but larger amount
  in tears, milk, saliva, mucus and the lining
  tissues
• 3) IgM First Antibody secreted during the
  primary response
• 4) IgE Found mainly in body fluids and skin ---
  Associated with allergy reactions!
• 5) IgD Found in B-Cell membrane

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Antibody structure
Binding site for the antigen
Binding site for the receptor
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(No Transcript)
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Primary and secondary responses to an antigen
Primary response first response when hosts
B-cell recognize the antigen
Secondary response upon second exposure to the
antigen, the Memory cells will divide, thus make
more of the total antibody
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Nature of IgE Allergic Reactions
Antigen IgE Mast cells Mediator
release Mediators histamine and others
Picture credit from Dr. Gary E.
Kaiser http//www.cat.cc.md.us/courses/bio141/lecg
uide/index.html
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What does histamine do?

• Vasodilation, increased capillary permeability,
  bronchoconstriction etc.

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Types of food allergies

• Immediate hypersensitivity with IgE which occurs
  within minutes to a few hours after ingestion of
  offending foods.
• Systemic Itching, urticaria (hives), Vomiting,
  Abdominal cramps, diarrhea and respiratory
  distress, and in severe cases anaphylactic shock
• Localized hives and eczema or atopy (an umbrella
  term covering clinical presentations of food
  allergy etc)
• Delayed hypersensitivity reactions (gt8hours after
  ingestion) cellular immunity involving
  T-lymphocytes and macrophages

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Lymphocytes
B lymphocytes mature in Bone marrow
and lymphatic tissue (spleen and lymph nodes) T
lymphocytes mature in the Thymus
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T-lymphocytes
Mature in Thymus, which is most active just
before and after birth. The thymus starts to
shrink during puberty.

• Helper T-Cells
• Recognise antigens on surface of leukocytes,
  especially macrophages
• Enlagre and form a clone of T-helper cells
• Secrete interferon and cytokines which stimulate
  B-cells and stimulate killer -cells
• Can be infected by HIV

• Killer T-Cells
• Also called cytotoxic
• Destroy abnormal body cells, e.g. virus infected
  or cancer cells
• Stimulated by cytokines (THcells)
• Release perforin, which forms pores in target
  cells. This allows water and ions in lysis

• Suppressor T-Cells
• Control the immune system when the antigen
  /pathogen has
• been destroyed
• Only recently discovered so
• little is known about them

• Memory T-Cells
• Can survive a long time and give lifelong
  immunity from infection
• Can stimulate memory B-cells to produce
  antibodies
• Can trigger production of killer T cells

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How T-cells work
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Stages of food allergy or hypersensitivity

• A. Sensitization initial meeting of an allergen
  and the immune system that results in IgE
  production!
• B. Activation of mast cells
• IgE
• Non-IgE substances (eg. Drugs)

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Most common sites for allergic reactions
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Symptoms-Food Allergy

• Nausea
• Diarrhea
• Abdominal cramps
• Pruritic rashes
• Angioedema
• Asthma/rhinitis
• Vomiting
• Hives
• Laryngeal edema
• Anaphylaxis

Exercise exacerbates symptoms
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Anaphylaxis

• Potential fatal reaction to a food allergen
  causing reduced oxygen supply to the heart and
  other body tissues.
• Symptoms include difficult breathing, low blood
  pressure, pale skin, a weak rapid pulse, loss of
  consciousness, death.

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Most common allergenic foods

• Legumes (Peanuts and Soybeans)
• Mollusks and shellfish (snails, mussels, oysters,
  scallops, clams, squid)
• Milk
• Eggs
• Fish (cod, salmon, haddock etc)
• Crustacea (shrimp, crawfish, lobster etc.)
• Wheat
• Tree nuts (almonds, walnuts, Brazil nuts etc)
• Selected food additives

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Children and Good Allergy

• High prevalence in the first few years of life
• Immature immune system and immature digestive
  system
• Cows milk and soy, most common allergens
• Breast feeding is recommended
• Delay introduction of common allergenic foods
• Sensitivity to most of the allergenic foods is
  usually lost by young children as they grow up

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Cross-Reaction the reaction of one antigen with
antibodies developed against another antigen.
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Cross-Reaction
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Hidden food ingredients in ready made food
products

• Milk and milk product derivatives
• Egg and egg derivatives
• Peanuts, tree nuts and derivatives
• Fish derivatives (surimi, fish sauce, fish paste
  etc)
• Soy and its derivatives

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Eating out is a nightmare?

• African, Chinese, Indonesian, Mexican, Thai, and
  Vietnamese dishes often contain peanuts. It is
  recommended that peanut-allergic individuals
  avoid these types of foods and restaurants.
• For traditional food restaurants,
  cross-contamination of allergens to other foods
  can also a problem.

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Solutions

• People who have food allergy need a total
  avoidance of the offending foods.
• Read food ingredient list.
• Eliminate cross-contamination during cooking and
  preparation!!!!

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Common prescribed medications

• epinephrine (relaxes smooth muscle, constricts
  blood vessels, and stimulates the heart used for
  severe systemic reactions-anaphylaxis)
• antihistamines (block the binding of histamine
  to histamine receptors on target cells)
• sodium cromolyn (prevents mast cells from
  releasing histamines).

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Other types of food allergy, Non-IgE Mediated

• Immune Complex-mediated
• Symptoms usually gastrointestinal
• Delayed type hypersensitivity
• Symptoms usually gastrointestinal

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Food Aversion

• A strong desire to avoid a particular food

Food Intolerance
Adverse reaction to food that does not involve
the immune system
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Food Intolerance

• Direct effect of food
• Enzyme deficiency (e.g., lactase, sucrase etc)
• Symptoms of food intolerance bloating, cramping,
  gas and diarrhea
• Main cause of food intolerance carbohydrates
  (lactose, fructose, sorbitol)

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Allergy VS Intolerance

• True Allergy-Total avoidance necessary!
• Intolerance- Small amount may be tolerated

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Diagnosis

• Determine if the symptoms are mediated by the
  immune system

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Other causes of allergy-like food problems

• Microbial products- e.g. histamine Some food
  products have high levels of histamine (eg
  fermented foods)
• Pharmacological reaction-tyramine,
  phenylethylamine, cafiene dose dependent
• Idiosyncratic reactions (adverse reactions of
  drugs etc dose dependent)
• Psychological disorders

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Diagnosis

• Determine if the symptoms are mediated by the
  immune system
• Complete physical
• Detailed case history
• Food diary
• Positive identification of the allergen

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Prick skin Test (PST)

• Drop of the substance under test on the forearm
• Allow a tiny amount to enter the skin (doctor
  pricks it with a needle)
• After 15min, verify presence of bump

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Radioallergosorbent Test (RAST)

• Requires blood samples
• Laboratory test are performed to look if the
  patients has IgE against specific types of food

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Resources for food allergies

• Food Allergy and Anaphylaxis network (FAAN)
• American Academy of Allergy, Asthma and
  Immunology
• American Dietetic Association
• Asthma and Allergy Foundation