Hypersensitivity Flashcards
Type I
allergic reaction that occurs minutes to hours after contact with allergen.
what is type I mediated by, which are produced in repsonse to allergen
IgE
What do IgE bind to on surface of mast cells and basophils
FceRI (high affinity receptors)
5 effector mechanisms underlying type I
- histamine release
- leukotriene release
- cytokine release (IL-4/5/13) - recruit th2 cells which make more cytokines and promote more IgE production
- eosinophil activation - recruited by IL-5. secrete toxic granules
- mucus production
3 type I symptoms
sneezing
itching
hives
anaphylaxis
Type II
immune-mediated reaction (antibody-dependent cytotoxicity) - kills cells and damages tissues
2 effector mechanisms underlying type II
- complement activation - forms membrane attack complex to lyse the target cell
- ADCC - abs recruit nk cells and macrophages to kill target cell
- opsonisation and phagocytosis - antibody-coated target cell recognised and engulfed by phagocytic cells (macrophages and neutrophils)
2 diseases caused by type II
HDN
Haemolytic anaemia
2 treatments for type II
blood transfusions
immunosuppressive therapy
type III
immune-mediated reaction - excess immune complexes in circulation
what do immune complexes activate in type iii, leading to tissue damage and inflammation
complement system
3 effector mechanisms underlying type III
- complement activation - activated by ICs, forms membrane attack complex
- neutrophil activation - release enzymes and ROS - damages tissues
- platelet activation and aggregation - damages tissues
- inflammatory cytokine release (IL1 and TNFa) - tissue damage and inflammation
2 type iii diseases
systemic lupus
rheumatoid arthiritis
what is type 4 hypersensitivity known as
delayed-type hypersensitivity
when does type 4 occur
When there’s a cell-mediated immune response against a foreign antigen + tissue damage
3 effector mechanisms underlying type 4
- T cell activation - proliferation and differentiation into cytotoxic T cells and t helper cells
- Cytotoxic T cell-mediated destruction - destroy cells that display foreign antigen = tissue damage
- t helper cell-mediated inflammation - t helper cells secrete cytokines (ifn-g, il-17) - activate macrophages and promote inflammation
- macrophage activation - activated by cytokines from T cells. Phagocytosis of foreign antigens and produce cytokines and ROS
some mechanisms both th2 immune responses and allergy share
- IgE production - th2 cells stimulate b cells
- eosinophils recruitment - cytokines produced by th2 cells recruit (il5)
- mucus production - th2 cells produce il13 - stimulates mucous production
- mast cell activation - activated by il4 produced by th2 cells. mast cells degranulate and release inflammatory mediators.
- basophils and dendritic cells recruitment - il-9 and il-3 produced by th2
what do IgE bind to on surface of mast cells and basophils, leading to their activation and degranulation and cytokines release
FceRI receptors
how do mast cells play important role in IS
releasing histamine and cytokines - recruit other immune cells and clear pathogens
Produce growth factors and cytokines for tissue repair
what do eosinophils release once activated
release cytotoxic granules, cytokines and chemokine
what are main steps in IgE-mediated allergic responses
- sensitisation - allergen exposure and produce IgE specific to the antigen
- re-exposure - allergen binds to IgE on mast cells and basophils upon re-exposure
- cross-linking - allergen binds to IgE and IgE receptors cross-link and activates cells
- degranulation - granules released by mast cells and eosinophils - allergic reaction symptoms
- late phase response - several hours after allergen exposure - recruitment of other immune cells which release cytokines and chemokines that can cause tissue damage
what is the main trigger of IgE-mediated allergic responses that leads to mast cell activation and degranulation (allergy symptoms)
cross-linking of IgE receptors on the surface of mast cells and basophils by allergens
what is atopy the genetic predisposition of
to develop allergic diseases like hay fever, asthma and eczema (IgE production - trigger histamine release)
when does HDN occur
when incompatibilty between blood types of a mother and baby . (woman with Rh-neg is carrying baby with Rh-pos)
What develop in the mothers bloodstream in HDN which crosses placenta and attacks fetus RBCs
Rh antibodies
what is intrinsic allergic alveoli’s
allergic lung disease due to inhalation of allergens like dust
