1. Food Allergy: Symptoms and Immunological Mechanisms Janice M. Joneja, Ph.D., R.D. 2007

2. 2 Symptoms of Food Allergy Controversy among practitioners because there are no definitive tests for food allergy “Allergic diathesis” 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 Diathesis. 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 Definition of Terms European Academy of Allergy and Clinical Immunology 2001 Allergy is a hypersensitivity reaction initiated by immunologic mechanisms An adverse reaction to food should be called food hypersensitivity –When immunologic mechanisms have been demonstrated, the appropriate term is food allergy –If the role of IgE is highlighted, the correct term is IgE- mediated food allergy –All other reactions, previously sometimes referred to as “food intolerance”, should be referred to as nonallergic food hypersensitivity

16. 16 Definition of Terms (continued) European Academy of Allergy and Clinical Immunology 2001 Severe, generalized allergic reactions to food can be classified as anaphylaxis Anaphylaxis is a severe, life-threatening, generalized or systemic hypersensitivity reaction. Atopy is a personal or familial tendency: – to produce IgE antibodies in response to low doses of allergens, usually proteins – and to develop typical symptoms such as asthma, rhiniconjunctivitis (hay fever) or eczema/dermatitis

17. 17 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”

18. 18 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

19. 19 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

20. 20 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

21. 21 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)

22. 22 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

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

24. 24 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

25. 25 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

26. 26 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

27. 27 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 hypersensitivity reaction –in response to food this may be IMMEDIATE-TYPE ALLERGY or anaphylaxis

28. 28 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

29. 29 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

30. 30 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

31. 31 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

32. 32 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

33. 33 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

34. 34 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)

35. 35 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

36. 36 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

37. 37 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

38. 38 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”

39. 39 IgE-mediated hypersensitivity Intracellular Granules are Released

40. 40 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

41. 41 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

42. 42 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

43. 43 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)

44. 44 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 –Involved in inflammatory process in eczema

45. 45 Prostaglandins Chemoattractant : PGD2 Smooth muscle contraction and relaxation Dilation and constriction of blood vessels Increase vascular permeability Responsible for pain

46. 46 Summary: IgE-mediated 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

47. 47 Summary: IgE-mediated 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

48. 48 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

49. 49 IgG-mediated 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

50. 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

51. 51 IgG-mediated 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

52. 52 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