foodallergiesinchildren-allergy,nutrition：儿童过敏的食物过敏，营养

Infant Food Allergies Where Are We Now?,Janice Joneja Ph.D., 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 2002 - 2007,3,Food Allergy in the Past 7 Years,Prevalence of food allergy highest in infants and toddlers Cows milk allergy incidence: 2.5% of infants Up to 8% of children under 3 years have allergy to a limited number of foods: Cows 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 2008,4,Age Relationship Between Food Allergy and Atopy,1,2,3,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,Age (in years),0,Relative Incidence,Asthma Rhinitis Eczema Food Allergy Anaphylaxis,Effect of Food Allergens,Effect of Air-borne 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: Intra-uterine life From birth to 2-3 years This meant reduction in exposure to highly allergenic foods: Mothers 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 2008,9,Education of the Immune System,Involves a complex 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 2007,10,T-helper Cell Subclasses,There are two subclasses of T-helper 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 IL-4,11,Role of 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 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 IL-10 and IL-13 may also be involved in tolerance These also regulate immune response to resident microflora, preventing the usual immune inflammatory response to microorganisms,_ Strobel and Mowat 2006,13,Oral Tolerance,“Education” of the T cells to not respond to that food protein when it enters via the oral route called oral tolerance Contrasts with the active immune responses needed to protect the gut against continual bombardment by invading pathogens and their products (toxins, etc) Also contrasts with the reduced responsiveness to the millions of microorganisms that are permanent residents of the large bowel T cells involved in these processes are called regulator T cells (Treg),14,Prevention of Food Allergy in Clinical Practice,Significant change in directives within the past 5 years: Previously: Avoidance of allergen to prevent sensitization (allergen-specific IgE) Current: Active stimulation of the immature immune system to induce tolerance of the antigens in food,_ Rautava et al 2005,15,Factors Predictive of Allergy: High and Low risk Groups,Many factors investigated as possible predict