Hypersensitivities Flashcards
What are allergens?
innocuous antigens that cause allergic reactions
What are the Type I Immediate Hypersensitivity characterisitics?
most common, rapid onset, IgE-mediated, low does of small soluble and stable protein antigens favor IgE responses, Atopy means tendency to have IgE responses
What is the Type I Immediate Hypersensitivity mechanism for 1st exposure?
sensitization, and causes IgE production, activated CD4+ helper Th2 cells secrete IL-4 & IL-13 causing B cells to switch to IgE -> IgE binds Fc receptors for IgE on mast cells, basophils, and eosinophils
What is the Type I Immediate Hypersensitivity mechanism for 2nd exposure?
antigen crosslinks occupied Fc receptors activating mast cells ->degranulation releases histamine, heparin, tryptase, & TNF-a, immediate reaction
What is the Type I Immediate Hypersensitivity mechanism for late-phase reaction?
synthesis & release of lipid mediators from arachidonic acid cascade including leukotrienes ->eosinophils & basophils which also have Fc receptors for IgE may be recruited causing further damage
What is the Type I Immediate Hypersensitivity mechanism for chronic response?
possible chronic inflammation, mediated by cytokines from Th2 cells, and products from eosinophils & basophils
What are some examples of Type I?
Allergy test: wheal & flare reaction (local), Allergic rhinitis (hay fever), allergic asthma, food allergens, Urticaria (hives), anaphylaxis (blood borne allergens), anaphylactic shock
What are characteristics of Type II Hypersensitivity?
IgG-mediated, IgG binds host cells
What are the mechanisms of Type II Hypersensitivity?
small antigenic molecule (non-self) binds cell surface molecules, allergen can behave as hapten, classical complement pathway, opsonization/phagocytosis
Type III Hypersensitivity characteristics?
like Type II it involves IgG but do NOT bind host cells, immune complex-mediated
What are the mechanisms of Type III Hypersensitivity?
immune complexes composed of IgG and antigen deposit in blood vessel walls -> classical complement pathway, C3a, C4a & C5a activate mast cells causing causing degranulation and secretion of inflammatory mediators -> macrophages & neutrophils enhance inflammatory response
What are examples of Type III Hypersensitivity?
Arthus reaction, Serum Sickness (most common, requires higher does than Type II), Farmer’s lung (chronic exposure to inhaled allergen)
What are the characteristics of Type IV Hypersensitivity or Delayed-Type?
reactions starts 1-3 days after antigen exposure, T cell-mediated (CD4+ helper Th1 and or CD8+), requires much higher dose than antibody-mediated hypersensitivities, associated with particular MHC alleles, most common are reactions localized to skin
What are the mechanisms of Type IV Hypersensitivity?
Th1 cells secrete inflammatory cytokines & active macrophages -> CD8+ T cells can kill host cells modified by antigen (antigen binds cell surface molecules and alters self antigens so they are not recognized)
What are examples of Type IV Hypersensitivity?
antigen gets below epidermis (Tuberculin test mediated by Th1 cells); contact hypersensitivity = contact dermatitis (topical exposure to antigen causes reaction)
