Lecture 4 - immunopathology + hypersensitivity Flashcards
what is allergy?
a reaction produced by the normal immune system (directed against innocuous antigens) in a pre-sensitised (immune) host
innocuous antigen
self tissue which the immune system recognises as foreign because it is overreacting
dendritic cell
cell that engulfs and presents material in its environment
T lymphocyte
engage and secrete chemicals
B lymphocytes
make antibodies
what type of antibody is involved in type 1 hypersensitivity?
IgE
what is the immunopathogenesis of type 1 hypersensitivity?
- IgE medicated mast cell and basophil degranulation
- release of preformed and de novo inflammatory mediators
what are the clinical features of type 1 hypersensitivity?
- fast onset
- weal and flare
which cells are involved in the late phase response of type 1 hypersensitivity?
- Eosinophils
- Th2 T cell –> a coordinator in this reaction
what is the primary response of type 1 hypersensitivity?
degranulation and releases:
- histamine
- proteases
- chemotactic factors
what is the secondary/ late (lipid mediators) response of type 1 hypersensitivity?
release:
- prostaglandin
- leukotrienes
what is released when IgE and receptor on mast cell cross link?
histamine, proteases, chemotactic factors by degranulation
cause symptoms of allergic reaction
what are the effects of histamine?
- bronchoconstriction
- increasing permeability of capillaries = swelling + lower BP
- swelling and inflammation, throat esp.
- increase HR
- may have blood clots, -gastric acid secretion
- diarrhoea
what are the 3 types of type 1 hypersensitivity?
- mild–> runny nose, itch, skin symptoms
- moderate
- severe –> anaphylaxis
anaphylaxis
an acute, potentially life-threatening, IgE medicated systemic hypersensitivity reaction
a medical emergency
urticaria
hive like over the skin
what are the symptoms of mild type 1 hypersensitivity?
- ichy eyes or nose
- cutaneous pruritus
- flushing
- urticaria
- oral tingling/pruritus
- abdo pain/naudea/vomiting
- runny nose, sneezing
what are the symptoms of moderate-severe type 1 hypersensitivity?
Anaphylaxis symptoms: prfound systemic reactions
- diffuse uriticaria and angioedema
- severe abdominal pain
- vomiting diarrhoea
- hoarseness cough
- SOB
- wheezing and cyanosis - respiratory arrest
- hypotension
- dizziness , loss of consciousness
- low BP
what is the first step in sensitisation reaction?
allergen presented to dendritic cells and presented to naive T cells
what do T cells differentiate into in sensitisation reaction?
Th2 cells
what do Th2 cells secrete in sensitisation reaction?
cytokines IL-4 and IL-13
what is the function of IL-4 and IL-13?
act as signal to naive B cells
what do naive B cells differentiate into in sensitisation reaction?
memory B cells with specific IgE that will recognise the allergen on further exposure
what is the change from B cell to memory cells called?
class switching because it moves from making IgM to IgE
what are antibodies?
proteins with capability to cause allergic reactions
what is the dual allergen exposure hypothesis?
This theory suggests that early cutaneous exposure to food protein through a disrupted skin barrier leads to allergic sensitisation.
Whereas early oral exposure to food allergen induces tolerance.
how is an allergy diagnosed?
- patch test
- skin prick test ( > 3mm wheal)
- intra-dermal test
- oral challenge test (gold standard)
- component resolved diagnostics
what is the atopic triad?
- asthma
- rhinitis
- eczema
asthma
disease of inflammation and hyperactivity of the small airways
which antigen causes the immediate symptoms of asthma?
IgE-mediated
which type of hypersensitivity is atopic dermatitis?
type 4 hypersensitivity
