Hypersensitivity Flashcards
(42 cards)
what is the function of the immune system?
to provide a robust defence against a wide variety of aggressive external agents (mainly microorganisms)
and internal aggressive agents (e.g. cancer)
what is consequence of immune recongition?
- intended destruction of antigen and collateral tissue damage
what is hypersensitivity definition?
immune response that results in bystander damage to self
- usually exaggeration of normal immune mechanisms
- pathophysiological basis for many chronic diseases including allergy & autoimmunity
what is Gel and Coombs classification?
-splitting of hypersensitivity into 4 types
Type I : Immediate hypersensitivity
Type II : Direct Cell effects
Type III : Immune Complex Mediated
Type IV : Delayed type hypersensitivity
what types of hypersensitivity are driven by antibodies?
Type I, II and III
(immediate hypersensitivity, direct cell effects, immune complex mediated)
what types of hypersensitivity are driven by T cells?
delayed type hypersensitivity (type $ only)
what are type 1 - immediate hypersensitivity reactions triggered by?
allergens e.g.
- House dust mite
- Pollen and animal dander
- Foods
- Drugs
- Latex
- Bee & wasp venom
what are allergens?
antigen that drives allergic reaction, many are soluble proteins that function as enzymes
what people are type 1 reactions prevalent in?
people who suffer from gentically predisposed so more likely to have lots of allergies
what type of antbiody is the only true allergic reaction response?
IgE mediated reaction
what does allergic IgE response cause?
atopic dermatitis, food allergy & allergic asthma
what are major players in type 1 hypersensitivity reaction?
IgE antibodies
mast cell degranulation in mast cells
effector T cells that are differentaited to CD4+
Eosinophil
B cell
what is the hygiene hypothesis?
in our modern westernised world, we’re too clean so develop allergies as from birth we’re not exposed to many allergies or parasites so never properly train our immune system
this means that in absence of parasitic infection, type 1 hypersensitivity reactions to innocuous (harmless) substances promote allergic reaction
what is Treg?
T regulatory cells -> t cells that regulate function of T & B cells in general
what are Th1 differentiation stimuli? what does that lead to? (from birth)
Th1 differentiation stimuli:
- older siblings (that are out in world)
-early daycare exposure
-rural environment
-childhood infections
-microbial pet exposure
- pets
= this means more balanced Treg activity and means Th2 is differentiated to Th1 (because of these stimuli) which means no allergies
what happens if lack of Th1 stimuli? what effect does this have? in what ways do babies/young children lack stimuli?
- by being an only child
- widespread use of ABX
-urban environment with allergen sensitization -> dust mites & cockroaches
=this means lack of Th1 stimulim and redcued Treg activity so Th2 not differentiated to Th1 so has things like allergy & asthma
what drives sensitization phase?
Th2 effector cells
what is the germinal centre?
a specialized microstructure that forms in secondary lymphoid tissues, producing long-lived antibody secreting plasma cells and memory B cells, which can provide protection against reinfection
what is Tfh cells function?
they’re specialized providers of T cell help to B cells, and are essential for germinal center formation, affinity maturation, and the development of most high affinity antibodies and memory B cells.
describe sensitisation stage of hypersensitivity type 1?
someone for example breathes in pollen and antigen presenting cell like macrophage or dendritic cell will present allergen derived peptide on MHC class II molecule and naive CD4+ T cell binds and
1.differentiates to Th2 cell which releases cytokines to switch B cell from producing IgM to IgE antibodies and will also release cytokines to stimulate eusinophils which release toxic granules
2. differentiates to Tfh cells which help B cells respond to allergen by releasing cytokines
then mast cells and basophils express receptors that bind to Fc region of IgE antibodies on their surface
- some residual IgE antibodies bind and this just means mast cells and basophils are geared up & ready
what happens in pathological stage when re-encounter of the allergen?
- Allergen binds to IgE-coated mast cells, &basophils→degranulation
- Release of vasoactive mediators (histamine, tryptase)
- Also increased expression of pro-inflammatory cytokines and leukotrienes
what effects does histamine cause?
increased vascular permability (which affects blood pressure & breathing)
smooth muscle contraction
what are generic features of symptoms of allergens?
- occurs quickly after exposure to allergen (minutes to 1/2 hours)
- responses are stereotyped
- may be associated with more than 1 organ system
- presentation is influenced by site of contact
- threshold for reactions may be influenced by co-factors such as exercise, alcohol & infection
what are specific symptoms from allergen?
- asthma
- Urticaria (hives - skin reaction)
- Angioedema (tissue swelling)
- Allergic rhinitis (hayfever)
- Allergic conjunctivitis (sore eye)
- Diarrhoea and vomiting
- Anaphylaxis (severe type of allergic reaction)
