hypersensitivity Flashcards
what is hypersensitivity?
state of altered reactivity in which the body reacts with an exaggerated immune response to a foreign agent
what is the difference between an allergy and an intolerance?
allergy causes an immune reaction, intolerances don’t
what does atopic mean ?
genetic disposition to an allergy
which type of hypersensitivity is an allergy?
type 1
type 1 hypersensitivity is mediated by what?
IgE
what is type 1 hypersensitivity?
allergic reaction provoked by reexposure to a specific type of antigen referred to as an allergen
which hypersensitivity is most common?
type 1
immediate hypersensitivity refers to which type?
type 1
atopy is associated with which typeof hypersensitivity?
type 1
type 1 hypersensitivity may cause what in extreme cases?
anaphylaxis
what is anaphylaxis?
acute serious allergic response
IgE is bound to 2 immune cells that allow it to cross link to antigens, what are these 2 cells?
mast cells and basophils
what is a hapten?
an organic molecule attached to a carrier protein which elicits an immunological reaction
some drugs may act as haptens, give an example of a drug and how it works?
penicillin - induce antibody mediated allergic reaction
the immune response in allergy begins with sensitisation, what happens to IgE during sensitisation?
- IgE producing B cells are activated after 1st exposure to allergen
- IgE binds to Fc receptor on mast cell or CD63 receptor on basophil
after sensitisation, elicitation takes place, what happens to IgE during this process?
- IgE recognises allergen and next exposure binds rapidly causing immediate degranulation
the priming of IgE to respond to an antigen is known as?
sensitisation
the storms cause by IgE are a result of what?
elicitation
mast cell degranulation releases what?
histamine, proteases, antimicrobial peptides
what is cutaneous atopy?
wheal and flare
what is urticaria?
itchy rash
what is allergic rhinitis?
hay fever
what is atopic dermatitis?
allergic eczema
what happens during anaphylactic shock?
mast cells degranulate all over the body
name 3 potentially fatal reactions that may occur as a result of anaphylactic shock and how they may cause death?
- laryngeal oedema (suffocation)
- bronchiole constriction (suffocation)
- peripheral oedema (fluid loss from BV causing hypertension and heart attack)
can can allergy be tested?
- skin prick test (prick with suspected allergen)
- blood test (measure IgE in response to allergen)
- patch test (allergen added to metal discs taped to skin)
- food challenge (in ITU setting)
what is the treatment for allergy?
- avoid allergen
- drugs
- immunological treatment
what drugs are used for allergy and how do they work?
anti histamine - compete with histamine for receptors
hydrocortisone - block histamine synthesis
cromoglycate - stabilise mast cells, stop histamine release
epinephrine - immediate treatment for anaphylactic shock
what immunological therapy is available for allergy treatment and how does it work?
hyposensitisation - repeat injection of allergen
- shift IgE to IgG
what type of drugs are antihistamines?
inverse agonists - inactivate receptors
what effect does epinephrine have on patients?
- bronchodilation
- reduce inflammatory mediators
what is type 2 hypersensitivity?
action of complement by IgG or IgM binding to antigenic cell, causing cell lysis
give an example of type 2 hypersensitivity?
blood transfusion
how does cell lysis occur during type 2 hypersensitivity reactions?
- activation of complement and formation of membrane attack complex (MAC)
- antibody dependant cell mediated cytotoxicity (NK cell)
what is type 3 hypersensitivity?
-antibody regulated reaction against soluble antigens circulating in serum
type 3 hypersensitive reactions result in the for formation of what?
antibody-antigen immune complexes that are deposited in organs
what effect do antibody-antigen immune complexes produced during type 3 hypersensitivity reactions have?
- activate complement
- induce neutrophil recruitment
- cause inflammatory damage
give 3 examples of conditions associated with type 3 hypersensitivity reaction?
- arthus reaction
- serum sickness
- oral erythma multiforme (EM)
is arthus reaction systemic or localised?
localised
is serum sickness systemic or localised?
systemic
what causes oral erythema multiform?
deposition of immune complexes (IgM) in microvasculature of oral mucosal membrane
what are the symptoms of oral erythema multiform?
crusty blistering of oral mucosa
hypersensitivity to injection causes which type of hypersensitivity response?
type 3
which immune cell mediates type 4 hypersensitivity?
T cells (CD4 and CD8)
delayed hypersensitivity refers to which type of hypersensitivity?
type 4
why us type 4 hypersensitivity referred to as delayed hypersensitivity?
takes time to recruit T cells
how is type 4 hypersensitivity tested?
patch test on back
type 4 hypersensitivity has a role in which systemic diseases?
- crohns
- TB
- sarcoidosis
