hypersensitivity Flashcards
what is hypersensitivity?
a state of altered reactivity in which the body reacts with an exaggerated immune response to a foreign agent
what is an allergen?
an antigen that causes an allergic reaction
describe type 1 hypersensitivity
most common, rapid, response to allegen, modulated by IgE, atopy=some indiciduals have a genetic predisposition for allergy, can lead to anaphylaxis
what are the 3 mechanisms of hypersensitivity?
allergens- can be proteins or haptens- small molecule that can be recognized by a specific antibody but has to be linked to a carrier to elicit antibody and/or T-cell responses IgE producing B antibodies activated during sensitization, class switching, IgE binds to Fc receptor on mast cell or CD63 on basophils, recognises allergen and next exposure binds rapidly and causes immediate degradation
type 1 examples
cutaneous atopy- allergic rhinitis, atopic dermatitis, astma,
systemic anaphylaxis- anaphylactic shock throughout body, arises from mast cell degranulation
describe the 3 methods of allergy testing
skin prick test and patch test
blood test
food challenge
what are the 4 anti-allergy drugs?
anti-histamines- compete for receptor
hydrocortisone-blocks histamine synthesis
cromoglicate-stabilises mast cells-stops histamine release
adrenaline-reverses effects of granules
what re the 2 immunological tx for allergy?
hypo/de-sensitisation-repeat injections of allergen
IgE to IgG-production
what does adrenaline do?
stimulates adrenoreceptors- improves peripheral vascular resistance
improves bp
reverses bronchodilation
reduces inflammatory mediator disease
what is type 2 hypersensitivity?
activation of complement by IgG or IgM binding to an antigenic cell
cell is lysed by membrane attack complex formation, antibody dependent cell mediated cytotoxicity
e.g transfusion reactions
what is the effect of antibody-antigen immune complex deposited in organs?
give examples
complement activation
neutrophil recruitment
inflammation-mediated damage
what is arthus reaction?
antibody-antigen complexes are localizes (eg bv walls)
can arise from injected particles, inhaled or ingested
what is serum sickness?
systemic form of arthus
antibody-antigen complezes circulate and lodge in many different tissues
similar mechanism occurs as localized form
what is oral erythema multiforme?
crusty blistering of oral mucosa
deposition of immune complexes in microvasculature of oral mucous membrane
acute inflammatory responses to viral infections
can be hypersensitivity to drugs
what is type 4 hypersensitivity?
T-cell mediated hypersensitivity (no antibodies)
takes time to recruit t cells
localized t cell reaction at site of antigen exposure
