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Food allergies
 

Food allergies

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  • Interferon – interferes with virus replication. The protein interferon, produced by animal cells when they are invaded by viruses, is released into the bloodstream or intercellular fluid to induce healthy cells to manufacture an enzyme that counters the infection. Interferon is therefore considered a potential medical resource as a BIOPHARMACEUTICAL. Cytotoxic – Greek – kytos = hollow, Toxikon = poison
  • Procedure: Prick tests (sometimes called scratch tests) are performed on the skin of the forearm or the back. Allergists put a small amount of an extract of a potential allergen into a shallow scratch. Within 15- twenty mins., a positive result will show as a hive, or wheal, on the scratch. The size of the hive may correlate with the intensity of the allergic reaction. In the event of a severe reaction, the allergist will administer a rescue medication such as epinephrine or an antihistamine . Severe reactions to a prick test, however, are uncommon

Food allergies Food allergies Presentation Transcript

  • Food Allergies Lecture 26 April 26, 2010 Dr. Ponnusamy
  • 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.
  • 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.
  • 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.)
  • 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.
    • 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)
    • 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 .
  • Specific Immunity Immunity Innate (inborn) Genetic factors Acquired Active (own Ab) Passive (Ready-made-Ab) Natural (Exposure to Foreign Agents) Artificial (immunization) Natural Maternal Ab Ab = Antibodies Artificial (Ab from Other sources)
  • 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
  • Antibody structure Binding site for the antigen Binding site for the receptor
  •  
  • Primary and secondary responses to an antigen Primary response : first response when host’s 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
  • 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/lecguide/index.html
  • What is Histamine? Histamine triggers the inflammatory response . Histamine is produced by basophils ( a type of white blood cell) and by mast cells ( a resident cell in tissues of the body; present more in skin, lungs, eyes, digestive tract, mouth, nose and conjunctiva) in response to antigens. Found in almost all animal body cells, histamine increases the permeability of the capillaries to white blood cells and other proteins, in order to allow them to engage foreign invaders in the affected tissues.
  • What does histamine do?
    • Allergic reactions are mediated by the release of mediators such as histamine
    • Vasodilation, increased capillary permeability, bronchoconstriction etc.
  • 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 (>8hours after ingestion): cellular immunity involving T-lymphocytes and macrophages
  • B lymphocytes – mature in B one marrow and lymphatic tissue (spleen and lymph nodes) T lymphocytes – mature in the T hymus Lymphocytes
  • T-lymphocytes
    • 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
    Mature in Thymus, which is most active just before and after birth. The thymus starts to shrink during puberty.
  • How T-cells work… Abnormal cell e.g cancer cell, infected cell Normal cell Antigen Killer T-cell recognises antigen Clones of killer T-cell attach to antigen Helper T-cell stimulates correct killer T-cell to multiply Killer T-cells release perforin pores Abnormal cell gains water, swells and bursts Helper T-cell also stimulates B-cells to make antibodies Memory T-cells stay in circulation Suppressor T-cells turn off immune response X X X
  • 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 : is specific for a particular allergen that triggers the allergic reaction. The allergen binds to the immunoglobulin on specific immune cells called basophils and mast cells. This binding results in the release of chemicals that cause inflammation in the body, such as histamine, within 30 minutes of exposure. These chemical mediators cause allergy symptoms, such as urticaria (hives), runny nose, watery eyes, sneezing, wheezing and itching.
      • Non-IgE substances (eg. Drugs)
  • Most common sites for allergic reactions
  • Symptoms-Food Allergy*
    • Nausea
    • Diarrhea
    • Abdominal cramps
    • Pruritic rashes
    • Angioedema
    • Asthma/rhinitis
    • Vomiting
    • Hives
    • Laryngeal edema
    • Anaphylaxis
    * Exercise exacerbates symptoms
  • 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.
  • 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
  • Children and Food Allergy
    • High prevalence in the first few years of life
    • Immature immune system and immature digestive system
    • Cow’s 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
  • Cross-Reaction: the reaction of one antigen with antibodies developed against another antigen.
  • Cross-Reaction
  • 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
  • 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 be a problem.
  • 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!!!!
  • 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).
  • Other types of food allergy, Non-IgE Mediated
    • Immune Complex-mediated
        • Symptoms usually gastrointestinal
    • Delayed type hypersensitivity
        • Symptoms usually gastrointestinal
      • Non-IgE substances related to food allergy
      • Food protein-induced Enterocolitis syndrome (FPIES)
    • Food protein proctocolitis/ proctitis (inflammation of rectum)
        • Rectum is the final portion of large intestine. It empties stools from body through anus
    • Food protein-induced enteropathy : Celiac disease , an adverse immune response to the protein gluten.
    • Milk-soy protein intolerance (MSPI): non-IgE mediated allergic response to milk and/or soy protein during infancy and early childhood. Symptoms of MSPI are usually attributable to food protein proctocolitis or FPIES.
    • Heiner syndrome - lung disease due to formation of milk protein/IgG antibody immune complexes (milk precipitins) in the blood stream after it is absorbed from the GI tract. The lung disease commonly causes bleeding into the lungs and results in pulmonary hemosiderosis.
  • A strong desire to avoid a particular food Food Aversion Adverse reaction to food that does not involve the immune system Food Intolerance
  • 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)
  • Allergy VS Intolerance
    • True Allergy-Total avoidance necessary!
    • Intolerance- Small amount may be tolerated
  • 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-tyr amine , phenylethyl amine , cafiene – dose dependent
    • Idiosyncratic reactions – (adverse reactions of drugs etc – dose dependent)
    • Psychological disorders
  • Diagnosis Determine if the symptoms are mediated by the immune system Complete physical Detailed case history Food diary Positive identification of the allergen
  • 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”
  • Radioallergosorbent Test (RAST)
    • Requires blood samples
    • Laboratory test are performed to look if the patients has IgE against specific types of food
    • It is a radioimmunoassay test
    • A person who has outgrown an allergy may still have a positive IgE years after exposure.
    • The suspected allergen is bound to an insoluble material and the patient's serum is added. If the serum contains antibodies to the allergen, those antibodies will bind to the allergen. Radiolabeled anti-human IgE antibody is added where it binds to those IgE antibodies already bound to the insoluble material. The unbound anti-human IgE antibodies are washed away. The amount of radioactivity is proportional to the serum IgE for the allergen.
  • Resources for food allergies
    • Food Allergy and Anaphylaxis network (FAAN)
    • American Academy of Allergy, Asthma and Immunology
    • American Dietetic Association
    • Asthma and Allergy Foundation