【正文】 Infant Food Allergies Where Are We Now? Janice Joneja ., RD 2 Food Allergy in the Past 7 Years ? Nearly 4% of North Americans have food allergies, many more than recorded in the past ? Incidence of food allergy much higher in children (8%) than adults (2%) ? Prevalence of peanut allergy doubled in American children younger than 5 years of age in the years 2022 2022 3 Food Allergy in the Past 7 Years ? Prevalence of food allergy highest in infants and toddlers ? Cow’s milk allergy incidence: % of infants ? Up to 8% of children under 3 years have allergy to a limited number of foods: ? Cow’s milk ? Wheat ? Egg ? Shellfish ? Soy ? Fish ? Peanut ? Tree nuts ? For every child who actually had a food allergy, over three more children were believed wrongly by their parents to suffer from the condition ______________ Venter et al 2022 4 Age Relationship Between Food Allergy and Atopy 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Age (in years) 0 Relative Incidence Asthma Rhinitis Eczema Food Allergy Anaphylaxis Effect of Food Allergens Effect of Airborne Allergens 5 Historical Perspective ? Sensitization to food allergens was thought to be the start of the “allergic march” Food allergy Atopic dermatitis/eczema Asthma Rhinitis ? Reducing sensitization to foods was therefore considered the essential first step in allergy prevention 6 Historical Perspective ? Measures of prevention were all designed to avoid sensitization to allergens during what were considered the most vulnerable periods: ? Intrauterine life ? From birth to 23 years ? This meant reduction in exposure to highly allergenic foods: ? Mother’s diet during pregnancy and lactation ? Delay in introduction of highly allergenic foods during weaning ? In spite of these stringent measures to prevent allergy, incidence of all types of allergies have increased significantly 7 Change in Direction During the Past Five Years ? Understanding of the importance of immunological sensitization and tolerance ? Recognition that tolerance not sensitization is the critical step in allergy prevention ? Finding that exposure to the allergenic food at an optimum stage is probably a critical step in allergy prevention ? Recognition that tolerance can be induced after allergy has been established – leading to important measures for allergy management 8 Allergy is a Response of the Immune System ? Our immune systems are designed to protect the body from invasion by foreign materials ? All foods contain proteins – derived from plants and animals – all of which are foreign to the human body ? In order for food to be absorbed, metabolized, and utilized by the body, the immune system needs to be “educated” that the foreign material is safe ________ Herz 2022 9 Education of the Immune System ? Involves a plex series of immunological reactions controlled by T cell lymphocytes (T cells) ? T helper (Th) cells detect foreign proteins (antigens) in any form ? T cells then trigger a series of immunological reactions, mediated by cytokines (the “control chemicals” of the immune system) _________ Joneja 2022 10 Thelper Cell Subclasses ? There are two subclasses of Thelper cells ? Th1 ? Th2 ? Each Th cell type produces its own specific set of cytokines ? The types of cytokines generated determine the resulting immune response ? Th1 principally INF? ? Th2 principally IL4 11 Role of Thelper 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 allergic (hypersensitivity) reaction ? IgE antibodies are produced 12 T cells involved in Oral Tolerance ? T cell response depends on the type of T helper cell that is activated ? Latest research indicates that T cells that produce a cytokine called TGF? are important in inducing oral tolerance ? Sometimes called Th3 cells ? T cells that produce IL10 and IL13 may also be involved in tolerance ? These also regulate immune response to resident microflora, preventing the usual immune inflammatory response to microanisms ______