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  1. 1. ALLERGY Mainul Husain Department of Animal & Poultry Science University of Guelph Ontario, Canada
  2. 2. What is Allergy? <ul><li>Allergy is hypersensitive reaction to foreign substances (antigens) , that in similar amounts and circumstances are harmless to other individuals </li></ul>Origin of the Word “Allergy” <ul><li>The word allergy is a combination of two Greek words: </li></ul><ul><li>“ Allos” - other and </li></ul><ul><li>“ Ergos” - action </li></ul>Some Allergic Conditions & Symptoms <ul><li>Some serious allergic diseases are: asthma, dermatitis, bee sting allergy, food allergy, conjunctivitis, and severe systemic anaphylaxis </li></ul><ul><li>Some common symptoms of allergy are: nose itching, sneezing, burning sensation, production of watery or mucous excretion, and possibly altered condition of other organs </li></ul>
  3. 3. Why Allergy Is Important? <ul><li>Allergy affects approximately 15-30% of the general population around the world majority of them are children </li></ul><ul><li>Most allergies interfere with sleep, intellectual functioning and recreational activities, whereas food allergy leads to considerable anxieties and fear of accidentally ingesting some notorious allergen </li></ul><ul><li>Allergies are chronic conditions and require changing of lifestyle or even profession, adhering to a diet and maintaning allergen avoidance </li></ul><ul><li>The cost of treating allergy just in the United States approximates US$6 billion dollars per annum. </li></ul>
  4. 4. Types of Allergy: <ul><li>There are four types of allergic reactions: </li></ul><ul><li>Type-1 allergic reaction (immediate, anaphylactic) : D evelops when the allergen stimulates the organism to produce IgE. It is also known as IgE mediated, immediate or anaphylactic reaction </li></ul><ul><li>Type-2 allergic reaction (cytotoxic) : Develops when the allergic reaction is accompanied by the appearance of IgG or IgM class immunoglobulins. These antibodies react with allergens on the surface of the blood cells or bone marrow cells membranes and causing them to undergo lysis </li></ul><ul><li>Type-3 allergic reaction : Develops when allergen reacts with IgG, IgM, IgA or IgE forming immune complexes that are deposited in tissues and initiate inflammations </li></ul><ul><li>Type-4 allergic reaction : It is also known as a delayed or cellular reaction. T lymphocytes play main role in this type of allergic reaction when they encounter specific allergen, by secreting cytokines triggering inflammatory reaction in tissues. </li></ul>
  5. 5. Types of Allergen <ul><li>There are 2 types of Allergens: (a) Allergens from the natural environment and (b) Allergens from a chemical environment </li></ul><ul><li>(a) Allergens from the natural environment : These are of high-molecular weight compounds, molecular weight higher than 10 kDa. Most of these allergens have an enzymatic function in their natural state. Few examples are: pollen of different plants, mould fungi spores, bacteria, house dust mites, epidermis of house pets, insect venom, some food proteins, etc. </li></ul><ul><li>(b) Allergens from a chemical environment : These are usually low-molecular chemical compounds, less than 1 kDa. They usually bind with a large protein and exert allergenic effect. Few examples are: metals, drugs, additives to food products, latex, aldehydes. </li></ul>
  6. 6. Food Allergy <ul><li>Food allergy is considered as a major health concern in modern medicine. About 1-2% of the adults and about 5-8% of the children of 3 years age are affected by food allergy around the world. </li></ul><ul><li>Immunologically food allergy may be classified in two types : </li></ul><ul><ul><li>IgE mediated food allergy : Occurs in two phases - </li></ul></ul><ul><ul><li>Sensitization phase : An IgE-response is generated towards a target food allergen. </li></ul></ul><ul><ul><li>Challenge phase : Occurs when the sensitized person is re-exposed to the same food allergen, and pre-existing IgE binds the target macromolecules, triggering the release of histamine and other inflammatory mediators. </li></ul></ul><ul><ul><li>Non-IgE-Mediated food allergy : This type of reaction is a cell-mediated reaction that involves the sensitized lymphocytes in tissues. The onset of symptoms occurs more than 8 hours after ingestion of the allergen food. </li></ul></ul>
  7. 7. Characteristic of Food Allergens <ul><li>Almost all food allergens are proteins with high stability due to the presence of intra-molecular disulfide bonds. </li></ul><ul><li>Most all food allergens have the following properties: </li></ul><ul><ul><li>Low molecular weight glycoproteins </li></ul></ul><ul><ul><li>Soluble </li></ul></ul><ul><ul><li>Acidic iso-electric points </li></ul></ul><ul><ul><li>Have multiple, linear IgE binding epitopes </li></ul></ul><ul><ul><li>Resistant to proteolytic digestion, heat and acidic conditions </li></ul></ul>
  8. 8. Foods Causing Allergy <ul><li>There are mainly 8 types of foods that cause about 90% of the food allergies: </li></ul><ul><ul><li>Foods of plant origin such as peanuts, tree nuts, wheat and soy. </li></ul></ul><ul><ul><ul><li>Plant food allergens: 7S Ara h 1 for peanut ,  -conglycinin for soy prolamins from wheat etc. </li></ul></ul></ul><ul><ul><li>Foods of animal origin such as cow’s milk, egg, fish and shellfish. </li></ul></ul><ul><ul><ul><li>Animal food allergens:  -lactoglobulin, α-lactalbumin and casein from milk, parvalbumin in fish, ovomucoid (Gal d 1) and ovalbumin (Gal d 2) in egg, tropomyosin in shellfish and seafood are the major allergen proteins from foods of animal origin. </li></ul></ul></ul>
  9. 9. Cells Involved In Allergic Reactions <ul><li>CD4 + T cells play the central role in allergic inflammation. </li></ul><ul><li>Two types of CD4 + : </li></ul><ul><ul><li>T helper-1 (Th1) - Produces IL-2, TNF-  , and interferon-  (IFN-  ). Antagonize the allergic response. </li></ul></ul><ul><ul><li>T helper-2 (Th2) : Produces IL-4, IL-5, IL-6, IL-9, IL-10, and IL-13. IL-4 and IL-13 play the main role in allergic response. </li></ul></ul>
  10. 10. A brief overview of T-cell differentiation and their route to allergy development IL-12 IL-4 ThP Cell Th2 Cell Th1 Cell IL-2 INF-  TNF LT IL-4 IL-5 IL-6 IL-9 IL-13 Predominant Antibody Response IgG2a IgE, IgG1 Biological Role Defense against intracellular pathogens Defense against large extracellular pathogens
  11. 11. Cellular & Molecular Mechanism of Allergy IL-4 IL-13 INF-  IL-12 IL-12 IL-10 Allergen Bacteria/Viruses Dendritic Cell Dendritic Cell Th2 Cell Th1 Cell B Cell IgE IL-3, IL-4, IL-6, IL-9 Mast Cell IL-3, IL-5, GM-CSF Allergen Eosinophil Inflammatory Mediators