Food Allergy

1. Food Allergy medslides.com

2. Definition of food allergy • An allergic reaction to a food can be described as an inappropriate reaction by the body's immune system to the ingestion of a food that in the majority of individuals causes no adverse effects. • An allergy is therefore a harmful immune response to an antigen that is not itself intrinsically harmful. medslides.com

3. Food allergy • Notably common during the first two years of life, when the gut barrier is immature • among infants and toddlers food reactions 6% to 8% cow’s milk 2% to 2.5% eggs 1.7% to 2% peanuts 0.6% tree nuts 0.6% • by age 10, many children outgrow food allergy, especially to egg or milk medslides.com

4. Food allergy • 20% to 25% of American public reports being allergic to one or another food • careful studies, with oral challenge, demonstrate actual food allergy in 2% to 2.5% of the population • food allergy is the leading cause of anaphylaxis requiring accident and emergency visits - with twice the incidence, and three times the mortality, of anaphylactic reaction to bee sting • 100 to 125 persons die of food reactions each year medslides.com

5. Food allergens • food allergens are glycoproteins • egg glycoproteins: ovomucoid, ovalbumin, ovotransferrin, lysozyme • milk casein glycoproteins • peanut glycoproteins: vicilin, conglutin, glycinin • a given food may contain 10 to 30 glycoproteins • food allergens have some resemblance to pollen proteins medslides.com

6. broad-spectrum of syndromes include hives “the classic food reaction”, unexplained wheezing or eczema, gastric complaints, and oral allergy symptoms • milk-allergy has been associated with nausea, vomiting, diarrhoea, bloating, early satiety, reflux, oesophagitis, gastritis, malabsoption, abdominal pain, and bloody stool • “oral allergy syndrome” include itching of the mouth, and swelling of the tongues and lips - associated with eating FRESH apple, carrots, hazelnut, bananas, melons medslides.com

7. Immunobiology • Antibodies recognize antigens as • linear epitope: an amino acids sequence • conformational epitope: amino acids sequence with a specific 3-dimensional shape. The 3D-shape may alter absorption or be denatured by heat medslides.com

8. Mechanisms of food allergy Allergic reactions to foods vary in severity and can be potentially fatal. The immune system does not recognize as safe a protein component of the food to which the individual is sensitive (such as some proteins in peanuts)- called the allergen. The immune system then typically produces immunoglobulin E (IgE) antibodies to the allergen, which trigger other cells to release substances that cause inflammation. medslides.com

9. Immediate (type I) hypersensitivity • The immune system is tilted toward the production of T helper cells of the Th2 subtype. • These release interleukin 4 (IL-4) and interleukin 13 (IL-13) on the B cell causing it to synthesise IgE antibodies. medslides.com

10. Immediate (type I) hypersensitivity • When these cell-bound antibodies encounter allergens, the mast cells discharge their granules releasing histamine and leukotrienes. • This causes local anaphylaxis: swelling, redness, and itching. • Some allergens including peanut proteins can precipitate such a massive IgE-mediated response that a life-threatening collapse of the circulatory and respiratory systems may occur. medslides.com

11. Immediate (type I) hypersensitivity • Immediate or type I hypersensitive reactions occur quickly after exposure to the allergen. • They are usually mediated by antibodies of the IgE class. • The constant region of IgE antibodies has a binding site for a receptor present on the surface of basophils and their tissue equivalent - the mast cell. medslides.com

12. Immunobiology • gastrointestinal manifestations of food allergy tend to be cell mediated (T-cells, monocytes and macrophages) • Non-gastrointestinal manifestations tend to be IgE mediated medslides.com

13. Investigation • History not only helps to pinpoint the suspected food allergen, but also to suggest whether or not the disorder is IgE-mediated • Endoscopy, the next step in evaluating non-IgE food reactions, may confirm the diagnosis histopathologically • Skin testing is the next step in evaluating suspected IgE-related disorders. A positive skin test does not confirm the presence of allergy. Only 40% of patients with a positive skin test to a food allergen turnout to be reactive when the food is ingested. The other 60% requires no further evaluation. medslides.com

14. Oral challenge For patients with positive skin test or endoscopic findings • unblinded oral challenge - eat small amount of the food under clinical observation, if positive then perform • single-blinded oral challenge • to distinguish patient with true food allergy • various strategies to disguise adequate quantities (10 grams) of the food being tested - incorporate in pancakes, canned tuna fish, or medicine capsules medslides.com

15. Food allergy • When food allergy is confirmed, it almost always proves to be restricted to 1 or 2 foods • young children: milk, peanut, tree nuts, soy, and wheat account for about 90% of cases • adolescents and adults: peanut, fish, shellfish, and tree nuts accounts for about 85% medslides.com

16. Diagnostic Tests 3 reasons for performing diagnostic tests: • . educate patient to avoid allergen • . addressing risk of anaphylaxis • . discuss prospects for specific therapy medslides.com

17. Avoiding allergen • simply avoiding allergic food is not enough • must educate patient about specific allergen • caseins, the chief milk-curd proteins, are sometimes added to food to preserve a chunky consistency • inadvertent contamination in manufacturing, cooking, or serving process: peanut oil on cooking or serving utensils, spaghetti sauce with peanut butter as an ingredient • inadequate (or ignored) food labelling medslides.com

18. Risks of anaphylaxis • in general, anaphylaxis is unpredictable • may be life-threatening • 1/3 may be biphasic (may recur 90 min after initial response to epinephrine, then become unresponsive to repeated treatment) • protracted anaphylaxis occur in about 1/4 of anaphylactic episodes medslides.com

19. Individuals at risks for anaphylaxis • patients whose food reactions have had respiratory features such as difficulty breathing or throat tightness • patients who are asthmatic • patients allergic to peanut, fish, shellfish, or tree nuts - the allergies that patients tend not to outgrow medslides.com

20. Self injectable epinephrine • Patients judged to have a high risk of anaphylaxis should be equipped with self-injectable epinephrine • the device should be used whenever the patient believes a food reaction is beginning • in view of the threat of a biphasic reaction, patient should be educated to go to a hospital accident and emergency ward immediately afterward and be prepared to stay there for at least 4 hours medslides.com

21. Adrenaline or anti-histamine • Adrenaline (epinephrine) is a quick-acting hormone, produced it from the adrenal gland. It causes an increase in heart rate and broncho-dilatation, and vasoconstriction. • Administration during anaphylaxis can prevent falls in blood pressure and stop anaphylactic shock developing. medslides.com

22. Adrenaline or anti-histamine • Histamine is released from mast cells and causes some of the symptoms of allergic reactions. • As anti-histamines are taken orally they take about an hour to get into the bloodstream, and this is far too slow to save lives in serious reactions. • Anti-histamines also don't prevent all the effects of histamine, for example effects of histamine on the heart and blood pressure, in serious reactions. medslides.com

23. Prospects for specific therapy • Desensitisation • administration of allergens with amino acid substituion in their IgE-binding epitopes • DNA vaccination • to cause host-cell expression of allergenic proteins as an alternative desensitisation strategy • Anti-IgE therapy • monoclonal anti-IgE antibody is currently being tested in patients with peanut allergy medslides.com