1. Food Allergy: Symptoms and Immunological Mechanisms Janice M. Joneja, Ph.D., R.D. 2005

2. 2 Symptoms of Food Allergy Controversy among practitioners because there are no definitive tests for food allergy “Allergic diasthesis”defined as: –Rhinoconjunctivitis (hayfever) –Asthma –Atopic dermatitis (eczema) Other conditions, especially in the digestive tract and nervous system are considered more “subjective” and many practitioners dismiss them as “fictitious” or psychosomatic

3. 3 Examples of Allergic Conditions and Symptoms Respiratory Tract –Seasonal or perennial rhinitis (hayfever) –Rhinorrhea (runny nose) –Allergic conjunctivitis (itchy, watery, reddened eyes) –Serous otitis media (earache with effusion) [“gum ear”; “glue ear”] –Asthma –Laryngeal oedema (throat tightening due to swelling of tissues)

4. 4 Examples of Allergic Conditions and Symptoms Skin and Mucous Membranes –Atopic dermatitis (eczema) –Urticaria (hives) –Angioedema (swelling of tissues, especially mouth and face) –Pruritus (itching) –Contact dermatitis (rash in contact with allergen) –Oral allergy syndrome (irritation and swelling of tissues around and inside the mouth)

5. 5 Examples of Allergic Conditions and Symptoms Digestive Tract –Diarrhea –Constipation –Nausea and Vomiting –Abdominal bloating and distension –Abdominal pain –Indigestion (heartburn) –Belching

6. 6 Examples of Allergic Conditions and Symptoms Nervous System –Migraine –Other headaches –Spots before the eyes –Listlessness –Hyperactivity –Lack of concentration –Tension-fatigue syndrome –Irritability –Chilliness –Dizziness

7. 7 Examples of Allergic Conditions and Symptoms Other –Urinary frequency –Bed-wetting –Hoarseness –Muscle aches –Low-grade fever –Excessive sweating –Pallor –Dark circles around the eyes

8. 8 The Allergic Diasthesis. Food Allergy Atopic dermatitis (Eczema) Allergic rhinoconjunctivitis (hay fever) Asthma (cough; wheeze) Gastrointestinal symptoms Nervous system: Headaches Irritability Anaphylaxis Muscle pain

9. 9 Anaphylaxis Severe reaction of rapid onset, involving most organ systems, which results in circulatory collapse and drop in blood pressure In the most extreme cases the reaction progresses to anaphylactic shock with cardiovascular collapse This can be fatal

10. 10 Anaphylaxis Usual progress of reaction –Burning, itching and irritation of mouth and oral tissues and throat –Nausea, vomiting, abdominal pain, diarrhea –Feeling of malaise, anxiety, generalized itching, faintness, body feels warm –Nasal irritation and sneezing, irritated eyes –Hives, swelling of facial tissues, reddening –Chest tightness, bronchospasm, hoarseness –Pulse is rapid, weak, irregular, difficult to detect –Loss of consciousness –Death may result from suffocation, cardiac arrhythmia, or shock

11. 11 Anaphylaxis Up to a third of cases of anaphylaxis occur in response to foods Not all symptoms occur in each case Symptoms may appear in any order Severe reactions occur within minutes to up to an hour of ingestion of allergen Onset can be delayed for up to two hours The later the onset of symptoms after eating the food, the less severe the reaction In majority of cases of fatal anaphylactic reaction to food, patient was asthmatic Potential for anaphylaxis increases when patient is receiving desensitization injections and is allergic to wasp and bee venom

12. 12 Anaphylaxis Almost any food can cause anaphylactic reaction Some foods more common than others: Peanut Tree nuts Shellfish Fish Egg –In children under three years Cow’s milk Egg Wheat Chicken

13. 13 Exercise-induced Anaphylaxis Usually occurs within two hours of eating the allergenic food Onset during physical activity Foods known to have induced exercise-induced anaphylaxis: –Celery –Shellfish (shrimp; oysters) –Squid –Peaches –Wheat

14. 14 Emergency Treatment for Anaphylactic Reaction Injectable adrenalin (epinephrine) Fast-acting antihistamine (e.g. Benadryl) Usually in form of Anakit® or Epipen® Transport to hospital immediately Second phase of reaction is sometimes fatal, especially in an asthmatic –Patient may appear to be recovering, but 2-4 hours later symptoms increase in severity and reaction progresses rapidly

15. 15 Food Allergy & Food Intolerance DEFINITIONS: American Academy of Allergy and Immunology Committee on Adverse Reactions to Foods, 1984 Food Allergy “An immunologic reaction resulting from the ingestion of a food or food additive” Food Intolerance “A generic term describing an abnormal physiological response to an ingested food or food additive which is not immunogenic”

16. 16 Classification of Adverse Reactions to Foods According to the Pathogenic Mechanisms Adapted from Wuthrich, 1993 ADVERSE REACTIONS TO FOODS ALLERGY (Hypersensitivity) Immunological Reactions INTOLERANCE Non-Immunological Reactions Type IV (T-cells) Type I (IgE) Type ll/lll (IgM IgG) Physiological reactions Neurogenic Enzyme Deficiency (Metabolic) ANAPHYLACTIC REACTIONS ANAPHYLACTOID REACTIONS Contact allergy (contact dermatitis) Toxicity (food poisoning) Food aversion

17. 17 T- Cell Lymphocytes T cell lymphocytes are the “controllers” of the immune response There are two major classes of T cells, differentiated on the basis of their cell surface receptors: –Helper T cells (Th) Express CD4 receptor (CD4+) Act in conjunction with MHC class II molecules –Cytotoxic (Tc) and Suppressor (Ts) T cells Express CD8 receptor (CD8+) Act in conjunction with MHC class I molecules

18. 18 Immune Response in Allergy The Hypersensitivity Reactions: Antigen Recognition The first stage of an immune response is recognition of a “foreign antigen” T helper cells (CD4+ subclass) identify the foreign protein as a “potential threat” Cytokines are released The types of cytokines produced control the resulting immune response

19. 19 T-helper Cell Subclasses There are two subclasses of T-helper cells, differentiated according to the cytokines they release: –Th1 –Th2 –Each subclass produces a different set of cytokines

20. 20 Significant Cytokines of the T-Cell Subclasses TH1 subclass produces: »Interferon-gamma (IFN-  ) »Interleukin-2 (IL-2) »Tumor necrosis factor alpha (TNF  ) »IL-12 TH2 subclass produces: »Interleukin-4 (IL-4) »Interleukin-5 (IL-5) »Interleukin-6 (IL-6) »Interleukin-8 (IL-8) »Interleukin-10 (IL-10) »Interleukin-13 (IL-13)

21. 21 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 Type I hypersensitivity reaction (allergy) –IgE antibodies are produced

22. 22 TH1 TH2 Interactions Factors promoting: Th1 - Bacterial and viral infections - Maturation of the immune system - Antigen tolerance Th2 - Parasite infestations - Immature immune system - Sensitization to antigen

23. 23 TH1 TH2 Interactions Factors promoting: Th1 - Bacterial and viral infections - Maturation of the immune system - Antigen tolerance Th2 - Parasite infestations - Immature immune system - Sensitization to antigen Predisposing factors: - Genetic inheritance - Early exposure to allergen - Increased antigen uptake

24. 24 T-Cells in the Immune and Allergic Response Stage 1: Protein enters Antigen (protein molecule) enters body It is taken up by an antigen-presenting cell (APC) –Examples of APCs: Dendritic cells Monocytes and macrophages B cell lymphocytes Partial activation of the T-cell occurs

25. 25 T-Cells in the Immune and Allergic Response continued Stage 2: To respond or not? The new antigen is recognized by T-helper cells (CD4+) The antigen is compared to “self-antigens” and is identified as “self” or “foreign” If “foreign”, a second signal is supplied by the T-cells via the CD28/CD8 or CD40/CD40 receptor-ligand complex which leads to: ACTIVATION OF THE IMMUNE RESPONSE accompanied by cytokine and antibody production If “self”, no second signal is conveyed and the T- cells assume a temporary state of unresponsiveness

26. 26 Role of T-cell Lymphocytes When conditions interfere with the process of tolerance, T-cells are activated: A TH1 response (IgM and IgG with activation of the complement cascade) is likely to induce damage to the mucosa –in response to food this may be a PROTEIN-SENSITIVE ENTEROPATHY A TH2 response leads to an IgE-mediated (Type I) hypersensitivity reaction –in response to food this may be IMMEDIATE-TYPE ALLERGY or anaphylaxis

27. 27 T cells in Foetal Life Neonates with and without a family history of atopy display Th2 activity –various combinations of IL-4; IL-5; IL-9 are detectable –IFN  below level of detection Rationale: In a successful pregnancy the foetus is embedded in a Th2 cocktail: A Th1 environment may predispose to foetal rejection High levels of IL-4, IL-10, PGE 2 and progesterone maintains a barrier to Th1 response at the maternal-foetal interface

28. 28 Maturing of the Immune System Postnatally, Th1 response progressively increases with age However, remains “deficient” relative to adult levels for varying periods during childhood Deficit seems to be at the level of APCs, especially dendritic cells APC fails to provide appropriate immune- deviating signals during T cell activation This deficit is more pronounced in atopic individuals

29. 29 The Th2 Response in Allergy Synthesis of IgE Naïve B cells are activated by cytokines IgM is formed first Specific antibodies are then produced in a process of class switching, driven by exposure to specific antigens The immature B cell matures into a “virgin” B cell that expresses both IgM and IgD

30. 30 B cell Maturation and Production of Antibody In the presence of antigen, B cells expressing specific antibodies are selected Others are eliminated by apoptosis Class switching occurs at this stage The direction of switching is regulated by cytokines secreted by the Th cells –IL-4, and to a lesser extent IL-13 from Th2 cells causes switching to IgE –IFN  produced by Th1 cells inhibits switch to IgE

31. 31 Control of IgE Production Overproduction of IgE leads to hypersensitivity IgE mediates the release of inflammatory mediators from a variety of granulocytes, including: –Mast cells –Basophils –Eosinophils

32. 32 Conditions that may Induce T-cell Response in Food Allergy Inherited allergic potential Immaturity of the immune system (the TH2 response predominates in the neonate) Inflammatory conditions in the gut that interfere with the normal antigen processing pathway Immaturity of the digestive mucosa leading to hyperpermeability Increased uptake of antigens

33. 33 Immune Response in Allergy: Early Response Allergic responses are biphasic –Cytokines regulate each stage of the immune response Early Response –IgE-mediated activation of granulocytes (mast cells; basophils) –Release of inflammatory mediators (histamine; prostaglandins; leukotrienes)

34. 34 Immune Response in Allergy: Early Response continued Clinical manifestations: –Upper airways: sneezing, itching, rhinorrhoea, nasal congestion –Lower airways: bronchoconstriction, dyspnoea, wheezing, cough –Skin: wheal, flare, itching, reddening

35. 35 Immune Response in Allergy: Late Response Late Response –Mediated by chemotactic factors (chemokines; LTB 4 ; PGD 2 ) from early phase –Move lymphocytes, monocytes, neutrophils, basophils, eosinophils to reactive tissues –These new granulocytes release their own battery of inflammatory mediators –The allergic response is augmented –This can be the life-threatening stage of an anaphylactic reaction or an asthma attack

36. 36 Mast Cells  Central to inflammation and the allergic response  Release of mast cell mediators by allergen is the initiating step of the early phase response  Initiation and control of allergic inflammation is effected by mast cell generation of:  Histamine  Proteases  Eicosanoids (prostaglandins; leukotrienes)  Cytokines

37. 37 Mast Cells Filled with granules containing preformed inflammatory mediators in proteoglycan (mostly heparin) matrix When mast cell is activated: – Granules swell – Contents become solubilised – Individual mediators are expelled into the local extracellular environment –Process known as “degranulation”

38. 38 Mediator Release ALLERGEN + IgE MAST CELL CHANGE IN CELL ENERGY ADENYLATE CYCLASE-cAMP CALCIUM ENTERS CELL DEGRANULATION Pre-formed Mediators HISTAMINE HEPARIN CHEMOTAXINS ENZYMES : - PHOPHOLIPASE A2 Release of Inflammatory Mediators Secondary Mediators : PROSTAGLANDINS: PG-2 LEUKOTRIENES: LT-4 Arachidonic Acid

39. 39 Action of Inflammatory Mediators on Tissues:  Histamine  Vasodilation Swelling of tissues Increased vascular permeability –angioedema (swelling) –rhinitis (stuffy nose) –rhinorrhea (runny nose) –urticaria (hives) –otitis media (earache) Pruritus (itching) Flushing Reddening Antidote: Antihistamines Block histamine receptors (H 1 ; H 2 ) on reactive cells

40. 40 Inflammatory Mediators Enzymes Tryptase; chymase; carboxypeptidase; cathepsin G: –Act directly on tissues and cause damage Phospholipase A2 Acts on cell membrane and releases arachidonic acid Leads to production of secondary inflammatory mediators by two enzyme pathways: –Cyclo-oxygenase to prostaglandins –Lipoxygenase to leukotrienes

41. 41 Secondary Mediator Release Arachidonic acid Lipoxygenase LEUKOTRIENES LTA 4 LTB 4 LTC 4 LTD 4 LTE 4 Cyclo-oxygenase PROSTAGLANDINS (PG 2 ) PROSTACYCLIN (PGI 2 ) THROMBOXANE (TX)

42. 42 Action of inflammatory mediators:  Leukotrienes  LTB 4 : Chemotaxin: –Attracts more leukocytes to reaction site –Augments allergic reaction LTC 4 ; LTD 4 ; LTE 4 : –Smooth muscle contraction –Responsible for bronchospasm of asthma

43. 43 Prostaglandins Chemoattractant : PGD2 Smooth muscle contraction and relaxation Dilation and constriction of blood vessels Increase vascular permeability Responsible for pain

44. 44 Summary: Type I IgE-mediated Immediate Hypersensitivity Food allergen cross-links two IgE antibodies attached to Fc  RI receptors on mast cell Mast cells are degranulated and release preformed inflammatory mediators Secondary cells of inflammation (eosinophils, neutrophils, basophils, lymphocytes) are recruited by chemotactic factors including chemokines

45. 45 Summary: Type I IgE-mediated Immediate Hypersensitivity Results in local symptoms in the gut (abdominal pain; diarrhoea) Allows increased absorption of the same and other antigens through the gut epithelium Leads to systemic effects such as mast cell activation in – lungs : asthma – skin : urticaria, angioedema, eczema – multiple organ systems : anaphylaxis

46. 46 Type II Hypersensitivity: Antibody-dependent Cytotoxicity 1.IgM and IgG Immunoglobulins are made against tissue antigens or haptens 2.Damage occurs due to activation of the complement cascade 3.IgG and IgM antibodies against food antigens are common in health and disease 4.Tissue damage could occur if anti-food antibodies cross- react with tissue antigens, leading to an autoimmune response 5.Very little evidence exists to support this apart from a few cases of thrombocytopaenia (deficiency of blood platelets) in association with milk allergy

47. 47 Type III Hypersensitivity Immune complex-mediated reactions IgM and IgG antibodies are frequently formed against food antigens IgG4 subclass is a high-affinity antibody for food antigens When food antigens pass into circulation they complex with their homologous antibodies The immune complexes are usually rapidly cleared from circulation and do not cause any pathology

48. 48 Type III Hypersensitivity Continued Tissue damage may result if there are high concentrations of complexes High concentrations of complexes triggers the complement cascade Anaphylatoxins formed by the complement pathway induce release of inflammatory mediators

49. Sequence of Reactions in the Complement Cascade AntigenAntibody A (IgG or IgM) S Antigen - Antibody Complex AS AS, C1qrs AS, C1qrs, C4b, 2a AS, C1qrs, C4b, 2a, 3b AS, C1qrs, C4b, 2a, 3b, C5b AS, C1qrs, C4b, 2a, 3b, C5b, 6, 7 AS, C1qrs, C4b, 2a, 3b, C5b, 6, 7, 8, 9 Membrane damaged cell LYSIS C1q C1r +Ca ++ C1s C4 C2Mg ++ C4a C2b “Recognition Complex” Alternative pathway enters here C3 C3a Anaphylatoxin (degranulation) C5C5a Chemotaxin Anaphylatoxin (degranulation) C6 C7 C8 C9

50. 50 Type III Hypersensitivity Continued If antigen is present in excess, the immune complexes may be deposited in vessel walls where an inflammatory reaction with fever is provoked: –in skin: urticaria angioedema –in kidneys: albuminuria –in joints: arthritis

51. 51 Food Specific IgG and Tolerance Clinical evidence suggests that specific IgG to a food that previously triggered production of IgE is a sign of tolerance Theoretically: – Food antigen now elicits Th1 response rather than Th2 –Low level of IgG does not trigger complement cascade –Food antigen-IgG complex is removed in normal process of phagocytosis

52. 52 Foods Most Frequently Causing Allergy 1. Egg » white »yolk 2. Cow’s milk 3. Peanut 4. Nuts 5. Shellfish 6. Fin fish 7. Wheat 8. Soy 9. Beef 10. Chicken 11. Citrus fruits 12. Tomato

53. 53 Additional Factors Involved in Symptoms of Food Sensitivity 1.Increased permeability of the GI tract –Inflammation: Infection Allergy Autoimmune processes Other pathology –Immaturity (in infants) –Alcohol ingestion 2.Physical exertion

54. 54 Additional Factors Involved in Symptoms of Food Sensitivity 3.Stress 4.Level of inflammatory mediators released in response to several different foods concomitantly 5.Level of inflammatory mediators released in response to other allergy (e.g. inhalant)

55. 55 Type IV Hypersensitivity Cell-mediated delayed reaction Involves T-cell lymphocytes and cytotoxic cytokines Occurs 24-72 hours after exposure to antigen  reaction proceeds only as long as cells are in contact with allergen Most evident in skin and mucous membranes (rash and itching) Poison ivy rash; contact dermatitis (nickel, rubber, leather dyes, detergents, cosmetics) Reaction to foods in contact with lips, mouth, tongue, and possibly lining of digestive tract

56. 56 Type IV Delayed Hypersensitivity  Cause cell-mediated immune damage local to the site of antigen contact with sensitive cells  Food antigens shown to cause intestinal damage in animal models by this mechanism  Evidence of cell-mediated immune responses to proteins in cow’s milk allergy  May be involved in systemic nickel allergy causing atopic dermatitis  Hypersensitivity reactions are not mutually exclusive and two or more reactions may occur simultaneously or sequentially 

57. 57 Nickel Allergy: Contact dermatitis Nickel is a common cause of contact dermatitis in sensitized individuals Reaction occurs wherever the skin or mucous membrane is in contact with nickel Reaction is a cell-mediated response T-cells (CD8 type) release cytotoxic cytokines Itching, scaling, reddening at site of contact Reaction continues as long as tissues are in contact with nickel Allergen that causes contact dermatitis can be identified by patch tests

58. 58 Nickel Allergy : Atopic dermatitis  Some nickel-sensitive patients have dermatitis in areas not in contact with nickel  Suggested Mechanisms  Nickel may replace magnesium in magnesium deficiency Acts as co-factor in triggering complement cascade Results in release of inflammatory mediators Nickel is more powerful than magnesium in this role  Nickel stimulates production of leukotrienes by enhancing lipoxygenase enzyme activity Leukotrienes are principal mediators in atopic dermatitis

59. 59 Nickel in Foods  Up to half of nickel-sensitive people may benefit from a nickel-restricted diet  Opinions divided on what constitutes a nickel-restricted diet  One study indicated 600 mcg could induce a reaction  Another indicated 2,500 mcg required for a positive reaction

60. 60 Nickel in Foods Nickel content of foods is variable: Plants will reflect nickel content of soil Fish will reflect nickel content of water Processing will affect nickel content of prepared and manufactured foods: –Metal grinders in milling of flours –Metal utensils e.g. stainless steel cooking pots In practice, a nickel-restricted diet is difficult to devise and follow