Allergic Diseases Flashcards
Definition of allergy and hypersensitivity
Undesirable, damaging, discomfort-producing and sometimes fatal reactions produced by the normal immune system directed against the innocuous antigens in a pre-sensitised (immune) host
Type I hypersensitivity overview
Anaphylactic hypersensitivity involving IgE Exogenous antigen 15-30 minutes Causes wheals and flares Basophils and eosinophils involved Antigen example = pollen Disease example = allergic asthma
Type II hypersensitivity overview
Cytotoxic hypersensitivity Cell surface antigen Involving IgG, IgM Minutes-hours Causes lysis and necrosis Antibody and complement involved Antigen example = penicillin Disease example = erythroblastosis fetalis
Type III hypersensitivity overview
Immune-complex hypersensitivity Involving IgG, IgM Soluble antigen 3-8 hours Causes erythema, oedema, necrosis Complement and neutrophils involved Antigen example = mouldy hay Disease example = SLE, serum sickness
Type IV hypersensitivity overview
Delayed type hypersensitivity No antibodies involved Tissue and organ antigen 48-72 hours Causes erythema induration Monocytes and lymphocytes involved Antigen example = TB test, poison ivy Disease example = contact dermatitis
Immune response to parasitic disease
Increased IgE
Tissue inflammation with eosinophilia & mastocytosis, as well as basophil infiltration
Presence of CD4+ T cells secreting IL4, IL5 and IL13
Genetic influence on allergic disease
All polygenic
Only susceptibility, not cause
IgE production
Th2 cell triggers B cell with IL4 which then proliferates, producing IgE
Role of Th2 cell
Multiple cytokine release
Innate inflammatory response
Drive for immunoglobulin production
Atopic triad
Asthma, rhinitis, eczema
Two main groups of rhinitis
Allergic and non-allergic
Types of allergic rhinitis
Seasonal (pollen, moulds)
Perennial (house dust mite, animal dander)
Types of non-allergic rhinitis
Vasomotor Infective Structural Drugs Hormonal Polyps
Asthma
Inflammation and hyper-reactivity of small airways
Immediate symptoms are always IgE-mediated, damage to airways always due to late phase response.
Damaged airways are hyper-reactive to non-allergic stimuli eg. fumes
Three classes of dermatitis
Eczema (can be atopic or non-atopic), contact dermatitis (allergic or non-allergic), other dermatitis
Common allergy tests
Specific IgE testing
Skin prick test
Advantages and disadvantages of specific IgE testing
A - Safe
D - False negatives, false positives
Advantages and disadvantages of skin prick test
A - Quick, patient satisfaction
D - False negatives, false positives, antihistamines, slight risk
Types of adverse food reaction
Food intolerance (based on food characteristic e.g. caffeine or toxin) or host characteristic (e.g. lactase deficiency or psychological) Food allergy (IgE mediated inc anaphylaxis, mixed, or non IgE mediated)
Treatment of allergy
Symptomatic: Antihistamines, steroids, adrenaline
Specific: Immunotherapy
Indications for immunotherapy
Life threatening reactions to wasp and bee stings
Severe hay fever
Animal dander allergy
Contraindications for immunotherapy
Multiple allergies
Food allergies
Eczema
Spontaneous urticaria
Major food allergens
Cow's milk Egg Legumes (e.g. peanuts, soybean, tree nuts) Fish Crustaceans and molluscs Cereal grains
Clinical manifestations of adverse reactions to food
Gastrointestinal: vomiting, diarrhoea, oral symptoms
Respiratory: Rhinitis, bronchospasm
Cutaneous: urticaria, angioedema
Anaphylaxis
